Gene interactions can modify Mendelian ratios expected from monohybrid and dihybrid crosses. There are several types of gene interactions:
1. Complementary gene interaction results in a 9:7 ratio when two genes work together to produce a trait.
2. Duplicate gene action occurs when genes encode redundant functions, resulting in a 15:1 ratio.
3. Dominant gene interaction yields a 9:6:1 ratio when dominance of one gene masks the other.
4. Epistatic interactions alter Mendelian ratios by one gene modifying another's expression. This includes recessive epistasis (9:3:4 ratio) and dominant epistasis (12:3:1 ratio).
Penetrance and expressivity refer to how likely and how strongly, respectively, a genetic trait is expressed in individuals. Penetrance is the proportion of individuals with a genotype who exhibit the associated phenotype, ranging from complete (100%) to incomplete. Expressivity refers to how strongly or uniformly a phenotype is manifested across an individual's body. A phenocopy is an environmentally induced phenotype that resembles a genetically determined trait but is not inherited. Diabetes has an incompletely penetrant genetic basis but treating it with insulin produces a phenocopy of the non-diabetic phenotype.
This document discusses balanced lethal systems in organisms. It provides examples of balanced lethal systems in Drosophila involving the curly and plum genes, and in Oenothera plants. In Oenothera, there are two types of balanced lethal mechanisms - one involving gametic lethality and the other involving zygotic lethality. The balanced lethal systems ensure that only heterozygotes survive by eliminating homozygotes for lethal alleles.
This document discusses the genetic concept of pleiotropy. Pleiotropy occurs when a single gene has effects on multiple phenotypic traits. Mutation of a pleiotropic gene can impact some or all traits under its control. Examples given include the genetic disorder phenylketonuria, which is caused by mutation of a gene affecting the enzyme phenylalanine hydroxylase, resulting in both mental retardation and physical symptoms. Another example is Marfan syndrome, where mutation of the FBN1 gene leads to seemingly unrelated symptoms all tracing back to effects on connective tissue. Pleiotropy demonstrates how one gene can influence multiple characteristics through its effects on shared metabolic pathways and proteins.
QUANTITATIVE INHERITANCE - KERNEL COLOR IN WHEATNethravathi Siri
Nilsson-Ehle (1909) and East (1910, 1916) documented first significant evidence of
quantitative inheritance by their individual works in wheat.
Their analysis started from one-locus control which continued to two locus control
and concluded at three-locus control.
The document summarizes a case study where the whole genomes of six gamma-irradiated rice plants were sequenced to identify mutations induced by radiation exposure. High-quality sequencing data was obtained and analyzed to detect single nucleotide substitutions, short insertions/deletions, and structural variations compared to the reference genome. The identified mutations were further validated using PCR analysis. The study demonstrates how whole genome sequencing can be used to characterize mutations induced in plants by gamma radiation exposure.
This PPT consists of 15 slides only explaining Pleiotropy. This is a phenomenon when one gene controls more than one trait , the traits may be related .Generally one gene's product acts for many reactions and so can affect more than one trait. Examples can be seen in pea Coloured flower and pigmentation in leaf axil, frizzle trait in chicken, fur colour and deafness in cats,Human pleiotropic traits are PKU,Sickle cell Anaemia. HOsyndrome , p53 gene etc
after floral induction, the inflorescence meristem eventually forms the floral meristem. the process is controlled by an array of homeotic genes. this also involves microRNAs for their regulation
This document discusses polyploidy, specifically allopolyploidy. It defines polyploidy as having extra sets of chromosomes beyond the diploid amount. The two main types are autopolyploidy, which involves genome doubling within a species, and allopolyploidy, which involves hybridization between two distinct species. Allopolyploidy is much more common in plants than animals, making up about 80% of land plants. The document provides examples of allopolyploid species formation and their uses in plant breeding.
Penetrance and expressivity refer to how likely and how strongly, respectively, a genetic trait is expressed in individuals. Penetrance is the proportion of individuals with a genotype who exhibit the associated phenotype, ranging from complete (100%) to incomplete. Expressivity refers to how strongly or uniformly a phenotype is manifested across an individual's body. A phenocopy is an environmentally induced phenotype that resembles a genetically determined trait but is not inherited. Diabetes has an incompletely penetrant genetic basis but treating it with insulin produces a phenocopy of the non-diabetic phenotype.
This document discusses balanced lethal systems in organisms. It provides examples of balanced lethal systems in Drosophila involving the curly and plum genes, and in Oenothera plants. In Oenothera, there are two types of balanced lethal mechanisms - one involving gametic lethality and the other involving zygotic lethality. The balanced lethal systems ensure that only heterozygotes survive by eliminating homozygotes for lethal alleles.
This document discusses the genetic concept of pleiotropy. Pleiotropy occurs when a single gene has effects on multiple phenotypic traits. Mutation of a pleiotropic gene can impact some or all traits under its control. Examples given include the genetic disorder phenylketonuria, which is caused by mutation of a gene affecting the enzyme phenylalanine hydroxylase, resulting in both mental retardation and physical symptoms. Another example is Marfan syndrome, where mutation of the FBN1 gene leads to seemingly unrelated symptoms all tracing back to effects on connective tissue. Pleiotropy demonstrates how one gene can influence multiple characteristics through its effects on shared metabolic pathways and proteins.
QUANTITATIVE INHERITANCE - KERNEL COLOR IN WHEATNethravathi Siri
Nilsson-Ehle (1909) and East (1910, 1916) documented first significant evidence of
quantitative inheritance by their individual works in wheat.
Their analysis started from one-locus control which continued to two locus control
and concluded at three-locus control.
The document summarizes a case study where the whole genomes of six gamma-irradiated rice plants were sequenced to identify mutations induced by radiation exposure. High-quality sequencing data was obtained and analyzed to detect single nucleotide substitutions, short insertions/deletions, and structural variations compared to the reference genome. The identified mutations were further validated using PCR analysis. The study demonstrates how whole genome sequencing can be used to characterize mutations induced in plants by gamma radiation exposure.
This PPT consists of 15 slides only explaining Pleiotropy. This is a phenomenon when one gene controls more than one trait , the traits may be related .Generally one gene's product acts for many reactions and so can affect more than one trait. Examples can be seen in pea Coloured flower and pigmentation in leaf axil, frizzle trait in chicken, fur colour and deafness in cats,Human pleiotropic traits are PKU,Sickle cell Anaemia. HOsyndrome , p53 gene etc
after floral induction, the inflorescence meristem eventually forms the floral meristem. the process is controlled by an array of homeotic genes. this also involves microRNAs for their regulation
This document discusses polyploidy, specifically allopolyploidy. It defines polyploidy as having extra sets of chromosomes beyond the diploid amount. The two main types are autopolyploidy, which involves genome doubling within a species, and allopolyploidy, which involves hybridization between two distinct species. Allopolyploidy is much more common in plants than animals, making up about 80% of land plants. The document provides examples of allopolyploid species formation and their uses in plant breeding.
- Gene interactions refer to how genes collaborate or interact to influence phenotypes. There are several types of interactions including interactions between alleles, pleiotropy, sex-limited traits, and gene-environment interactions.
- Dominance relationships can be complete, incomplete, or codominant. Incomplete dominance results in intermediate phenotypes, while codominance allows both alleles to be expressed. Multiple alleles can form allelic series with different dominance hierarchies.
- Penetrance and expressivity describe how consistently and intensely a genotype is expressed as a phenotype, which can be influenced by environment and other genes. Gene-environment interactions are important, as the environment can modify gene expression and phenotypes.
Gene interactions occur when two or more different genes influence the outcome of a single trait
Epistasis is a phenomenon in which the expression of one gene depends on the presence of one or more modifier genes.
A gene whose phenotype is expressed is called epistatic.
A complementation test (sometimes called a "cis-trans" test) can be used to test whether the mutations in two strains are in different genes. By taking an example of Benzer's work, complementation has been explained.
Heterosis breeding-Classical and molecular concepts Rahul Chourasia
This document discusses heterosis (hybrid vigor) in plants. It begins by defining heterosis as superior performance of F1 hybrid plants compared to their parental inbred lines. It then discusses several historical concepts and models that have been proposed to explain the genetic basis of heterosis, including dominance, overdominance, epistasis, and molecular mechanisms involving gene expression, small RNAs, and epigenetics. It also discusses using QTL mapping to identify genomic regions contributing to heterosis. The document concludes with several case studies, including one on delayed flowering times in tomato plants that are heterozygous for the sft mutant gene.
The document discusses the concept of pleiotropy, which is when a single gene influences multiple phenotypic traits. It provides examples of pleiotropy, including phenylketonuria (PKU) where a single gene affects the ability to break down phenylalanine as well as mental retardation. Other examples given are the frizzled feather trait gene in chickens, sickle cell disease, the vestigial gene in fruit flies, and deafness associated with pigmentation in cats. The document concludes that Mendel's observations of traits being controlled by single genes was based on the phenomenon of pleiotropy.
Inability of a plant with functional pollen to set seed when self-pollinated.
Hindrance to self-fertilization.
Prevents inbreeding and promotes outcrossing.
Reported in about 70 families of angiosperms including crop species.
This document discusses polyploids, which are organisms with multiple sets of chromosomes beyond the typical diploid number. Polyploids can be classified as euploids, containing multiples of the full chromosome set, or aneuploids, containing extra or missing chromosomes. Euploids include autopolyploids, with multiple copies of the same genome, and allopolyploids, with genomes from different species. Polyploids occur naturally but can also be induced in crops to create advantages like seedlessness, hybrid vigor, and stress tolerance. While polyploids offer benefits to plant breeding, they also face challenges like reduced fertility.
Polygenic inheritance involves multiple genes contributing to a trait, as opposed to single-gene inheritance. It can result in continuous variation, where a wide range of phenotypes exist between extremes. Human skin color and wheat seed color are examples of polygenic traits that show continuous variation, with skin color determined by 3-4 genes influencing melanin production and seed color by 3 genes determining red pigment levels.
Cytoplasmic or extranuclear inheritance involves the transmission of traits controlled by genes located outside the cell nucleus, such as in mitochondria or chloroplasts. This form of inheritance does not follow Mendel's laws and instead is maternally inherited, with traits expressed based on the phenotype of the female parent. Examples discussed in the document include mitochondrial inheritance in humans, cytoplasmic factors influencing disease susceptibility in mice, and chloroplast genes controlling leaf color in plants.
This document summarizes key concepts related to chromosomes and chromosomal aberrations. It defines chromosomes as structures carrying genetic information in cells. Chromosomal aberrations refer to structural or numerical changes in chromosomes. Structural changes include deletions, duplications, inversions, and translocations that alter chromosome structure. Numerical changes include aneuploidy, where the number of individual chromosomes changes, and euploidy, where full sets of chromosomes are added or removed. Specific examples of structural and numerical aberrations in humans that cause genetic diseases are provided. The roles of chromosomal aberrations in evolution and crop improvement are also briefly discussed.
ABC model of flower development crop repro physionea killuae
The document discusses the ABC model of flower development. The ABC model proposes that three classes of genes (A, B, and C) interact to specify the four types of floral organs in flowers. Class A genes specify sepals, Class A and B genes together specify petals, Class B and C genes together specify stamens, and Class C genes specify carpels. Mutations in these genes result in homeotic transformations where one organ develops in the place of another. The ABC model was formulated based on studies of gene expression and mutants in Arabidopsis thaliana and Antirrhinum majus.
Polyploids are organisms with multiple sets of chromosomes beyond the diploid number. They occur naturally and provide mechanisms for adaptation. Euploids are the most common type of polyploid and contain multiples of the basic chromosome set. Autopolyploids contain multiple copies of the same genome, while allopolyploids contain genomes from different species. Polyploids have applications in plant breeding like inducing mutations, producing seedless fruits, and overcoming hybridization barriers. They provide advantages such as increased vigor and stress tolerance, but also drawbacks like effects on sterility and inheritance.
This document discusses distant hybridization, which involves crossing individuals from different plant species or genera. Some key points:
- The first recorded distant hybrid was between carnation and sweet william produced in 1717. An inter-generic hybrid called raphanobrassica was produced in 1928.
- Problems with distant hybrids include cross incompatibility, hybrid inviability, sterility, and breakdown in subsequent generations. Techniques like embryo rescue can help overcome some issues.
- Distant hybridization can be used to transfer beneficial traits like disease resistance between species. It has led to improvements in crops through hybrid varieties with increased yield, adaptation, and resistance to insects and disease.
1. The document discusses gene interactions and how they can modify Mendelian ratios by altering phenotypic expression. It provides examples of different types of epistatic interactions like complementary, duplicate, dominant, and recessive gene interactions.
2. It also covers complementation analysis, which is used to determine if two mutations that cause the same phenotype are in the same or different genes. If the mutations complement, producing wild-type offspring, they are in different genes, while failure to complement means they are in the same gene.
3. The functional consequences of mutations are described, including loss-of-function mutations like amorphic and hypomorphic, and gain-of-function mutations like hypermorphic and neomorphic.
Karyotype analysis and evolution by MannatMannatAulakh
A karyotype is the number and appearance of chromosomes in a cell and can provide information about an organism's species. Key features used to characterize karyotypes include chromosome size, centromere position, and banding patterns. Karyotypes can be symmetric or asymmetric and are often represented visually using idiograms or karyograms. Analysis techniques like G-banding stain chromosomes to reveal identifying patterns. Comparing karyotypes across species provides insights into evolutionary mechanisms like centric fusion and fission that alter chromosome counts. In primates, chromosomal changes like the fusion that formed human chromosome 2 are important in lineage evolution.
The document discusses the differences between prokaryotic and eukaryotic genomes. Prokaryotes generally have a single, circular chromosome while eukaryotes have multiple linear chromosomes within a membrane-bound nucleus. The human genome contains around 3 billion base pairs divided between nuclear and mitochondrial DNA. The nuclear genome encodes around 20,000-25,000 protein-coding genes and is inherited equally from both parents, while mitochondrial DNA is maternally inherited.
This document presents information on complementation tests. It defines complementation tests as a method used to determine if two mutations are in the same gene or different genes. It explains that if the mutations are complementary (in different genes), the offspring will show the parental phenotypes, but if they are not complementary (in the same gene), the offspring will show a new phenotype. Three examples of using complementation test results to determine the number of genes involved are provided. The document concludes by citing a reference for more information on assigning mutations to genes using complementation tests.
1. Genetic mapping involves determining the linear order and distance between linked genes on chromosomes through test crosses.
2. Key processes include determining linkage groups, calculating map distances in morgan or centimorgan units, and using two-point and three-point test crosses to order genes.
3. Maps are constructed by combining map segments and are useful for understanding inheritance, disease diagnosis, and evolution.
Gene interactions can occur between alleles at the same locus (intra-allelic) or between genes at different loci (inter-allelic). Intra-allelic interactions include complete dominance, incomplete dominance, codominance, and overdominance. Inter-allelic interactions include complementation where two dominant genes are required for expression, and epistasis where one gene masks the effects of another gene. Examples of epistasis discussed are dominant epistasis in fruit color of squash, and recessive epistasis in the Bombay phenotype in humans.
1) The document discusses various types of non-Mendelian gene interactions including incomplete dominance, co-dominance, supplementary interaction, complementary interaction, and epistasis.
2) In incomplete dominance, alleles are not completely dominant or recessive and produce an intermediate phenotype in heterozygotes, like pink flowers from red and white parents.
3) Co-dominance occurs when both alleles are fully expressed in heterozygotes, such as AB blood from alleles for A and B antigens.
4) Epistasis involves one gene masking the expression of another gene.
Este documento describe los conceptos de epistasis genética y dominancia. La epistasis ocurre cuando la expresión de un gen o par de genes enmascara o modifica la expresión de otro gen o par génico. Se presentan dos casos de interacción génica que ilustran tipos de epistasis: epistasis simple dominante y epistasis doble recesiva. Finalmente, se explican los diferentes tipos de interacciones epistáticas como epistasis simple dominante, epistasis simple recesiva y epistasis doble.
- Gene interactions refer to how genes collaborate or interact to influence phenotypes. There are several types of interactions including interactions between alleles, pleiotropy, sex-limited traits, and gene-environment interactions.
- Dominance relationships can be complete, incomplete, or codominant. Incomplete dominance results in intermediate phenotypes, while codominance allows both alleles to be expressed. Multiple alleles can form allelic series with different dominance hierarchies.
- Penetrance and expressivity describe how consistently and intensely a genotype is expressed as a phenotype, which can be influenced by environment and other genes. Gene-environment interactions are important, as the environment can modify gene expression and phenotypes.
Gene interactions occur when two or more different genes influence the outcome of a single trait
Epistasis is a phenomenon in which the expression of one gene depends on the presence of one or more modifier genes.
A gene whose phenotype is expressed is called epistatic.
A complementation test (sometimes called a "cis-trans" test) can be used to test whether the mutations in two strains are in different genes. By taking an example of Benzer's work, complementation has been explained.
Heterosis breeding-Classical and molecular concepts Rahul Chourasia
This document discusses heterosis (hybrid vigor) in plants. It begins by defining heterosis as superior performance of F1 hybrid plants compared to their parental inbred lines. It then discusses several historical concepts and models that have been proposed to explain the genetic basis of heterosis, including dominance, overdominance, epistasis, and molecular mechanisms involving gene expression, small RNAs, and epigenetics. It also discusses using QTL mapping to identify genomic regions contributing to heterosis. The document concludes with several case studies, including one on delayed flowering times in tomato plants that are heterozygous for the sft mutant gene.
The document discusses the concept of pleiotropy, which is when a single gene influences multiple phenotypic traits. It provides examples of pleiotropy, including phenylketonuria (PKU) where a single gene affects the ability to break down phenylalanine as well as mental retardation. Other examples given are the frizzled feather trait gene in chickens, sickle cell disease, the vestigial gene in fruit flies, and deafness associated with pigmentation in cats. The document concludes that Mendel's observations of traits being controlled by single genes was based on the phenomenon of pleiotropy.
Inability of a plant with functional pollen to set seed when self-pollinated.
Hindrance to self-fertilization.
Prevents inbreeding and promotes outcrossing.
Reported in about 70 families of angiosperms including crop species.
This document discusses polyploids, which are organisms with multiple sets of chromosomes beyond the typical diploid number. Polyploids can be classified as euploids, containing multiples of the full chromosome set, or aneuploids, containing extra or missing chromosomes. Euploids include autopolyploids, with multiple copies of the same genome, and allopolyploids, with genomes from different species. Polyploids occur naturally but can also be induced in crops to create advantages like seedlessness, hybrid vigor, and stress tolerance. While polyploids offer benefits to plant breeding, they also face challenges like reduced fertility.
Polygenic inheritance involves multiple genes contributing to a trait, as opposed to single-gene inheritance. It can result in continuous variation, where a wide range of phenotypes exist between extremes. Human skin color and wheat seed color are examples of polygenic traits that show continuous variation, with skin color determined by 3-4 genes influencing melanin production and seed color by 3 genes determining red pigment levels.
Cytoplasmic or extranuclear inheritance involves the transmission of traits controlled by genes located outside the cell nucleus, such as in mitochondria or chloroplasts. This form of inheritance does not follow Mendel's laws and instead is maternally inherited, with traits expressed based on the phenotype of the female parent. Examples discussed in the document include mitochondrial inheritance in humans, cytoplasmic factors influencing disease susceptibility in mice, and chloroplast genes controlling leaf color in plants.
This document summarizes key concepts related to chromosomes and chromosomal aberrations. It defines chromosomes as structures carrying genetic information in cells. Chromosomal aberrations refer to structural or numerical changes in chromosomes. Structural changes include deletions, duplications, inversions, and translocations that alter chromosome structure. Numerical changes include aneuploidy, where the number of individual chromosomes changes, and euploidy, where full sets of chromosomes are added or removed. Specific examples of structural and numerical aberrations in humans that cause genetic diseases are provided. The roles of chromosomal aberrations in evolution and crop improvement are also briefly discussed.
ABC model of flower development crop repro physionea killuae
The document discusses the ABC model of flower development. The ABC model proposes that three classes of genes (A, B, and C) interact to specify the four types of floral organs in flowers. Class A genes specify sepals, Class A and B genes together specify petals, Class B and C genes together specify stamens, and Class C genes specify carpels. Mutations in these genes result in homeotic transformations where one organ develops in the place of another. The ABC model was formulated based on studies of gene expression and mutants in Arabidopsis thaliana and Antirrhinum majus.
Polyploids are organisms with multiple sets of chromosomes beyond the diploid number. They occur naturally and provide mechanisms for adaptation. Euploids are the most common type of polyploid and contain multiples of the basic chromosome set. Autopolyploids contain multiple copies of the same genome, while allopolyploids contain genomes from different species. Polyploids have applications in plant breeding like inducing mutations, producing seedless fruits, and overcoming hybridization barriers. They provide advantages such as increased vigor and stress tolerance, but also drawbacks like effects on sterility and inheritance.
This document discusses distant hybridization, which involves crossing individuals from different plant species or genera. Some key points:
- The first recorded distant hybrid was between carnation and sweet william produced in 1717. An inter-generic hybrid called raphanobrassica was produced in 1928.
- Problems with distant hybrids include cross incompatibility, hybrid inviability, sterility, and breakdown in subsequent generations. Techniques like embryo rescue can help overcome some issues.
- Distant hybridization can be used to transfer beneficial traits like disease resistance between species. It has led to improvements in crops through hybrid varieties with increased yield, adaptation, and resistance to insects and disease.
1. The document discusses gene interactions and how they can modify Mendelian ratios by altering phenotypic expression. It provides examples of different types of epistatic interactions like complementary, duplicate, dominant, and recessive gene interactions.
2. It also covers complementation analysis, which is used to determine if two mutations that cause the same phenotype are in the same or different genes. If the mutations complement, producing wild-type offspring, they are in different genes, while failure to complement means they are in the same gene.
3. The functional consequences of mutations are described, including loss-of-function mutations like amorphic and hypomorphic, and gain-of-function mutations like hypermorphic and neomorphic.
Karyotype analysis and evolution by MannatMannatAulakh
A karyotype is the number and appearance of chromosomes in a cell and can provide information about an organism's species. Key features used to characterize karyotypes include chromosome size, centromere position, and banding patterns. Karyotypes can be symmetric or asymmetric and are often represented visually using idiograms or karyograms. Analysis techniques like G-banding stain chromosomes to reveal identifying patterns. Comparing karyotypes across species provides insights into evolutionary mechanisms like centric fusion and fission that alter chromosome counts. In primates, chromosomal changes like the fusion that formed human chromosome 2 are important in lineage evolution.
The document discusses the differences between prokaryotic and eukaryotic genomes. Prokaryotes generally have a single, circular chromosome while eukaryotes have multiple linear chromosomes within a membrane-bound nucleus. The human genome contains around 3 billion base pairs divided between nuclear and mitochondrial DNA. The nuclear genome encodes around 20,000-25,000 protein-coding genes and is inherited equally from both parents, while mitochondrial DNA is maternally inherited.
This document presents information on complementation tests. It defines complementation tests as a method used to determine if two mutations are in the same gene or different genes. It explains that if the mutations are complementary (in different genes), the offspring will show the parental phenotypes, but if they are not complementary (in the same gene), the offspring will show a new phenotype. Three examples of using complementation test results to determine the number of genes involved are provided. The document concludes by citing a reference for more information on assigning mutations to genes using complementation tests.
1. Genetic mapping involves determining the linear order and distance between linked genes on chromosomes through test crosses.
2. Key processes include determining linkage groups, calculating map distances in morgan or centimorgan units, and using two-point and three-point test crosses to order genes.
3. Maps are constructed by combining map segments and are useful for understanding inheritance, disease diagnosis, and evolution.
Gene interactions can occur between alleles at the same locus (intra-allelic) or between genes at different loci (inter-allelic). Intra-allelic interactions include complete dominance, incomplete dominance, codominance, and overdominance. Inter-allelic interactions include complementation where two dominant genes are required for expression, and epistasis where one gene masks the effects of another gene. Examples of epistasis discussed are dominant epistasis in fruit color of squash, and recessive epistasis in the Bombay phenotype in humans.
1) The document discusses various types of non-Mendelian gene interactions including incomplete dominance, co-dominance, supplementary interaction, complementary interaction, and epistasis.
2) In incomplete dominance, alleles are not completely dominant or recessive and produce an intermediate phenotype in heterozygotes, like pink flowers from red and white parents.
3) Co-dominance occurs when both alleles are fully expressed in heterozygotes, such as AB blood from alleles for A and B antigens.
4) Epistasis involves one gene masking the expression of another gene.
Este documento describe los conceptos de epistasis genética y dominancia. La epistasis ocurre cuando la expresión de un gen o par de genes enmascara o modifica la expresión de otro gen o par génico. Se presentan dos casos de interacción génica que ilustran tipos de epistasis: epistasis simple dominante y epistasis doble recesiva. Finalmente, se explican los diferentes tipos de interacciones epistáticas como epistasis simple dominante, epistasis simple recesiva y epistasis doble.
This document discusses gene interactions and epistasis. It provides several examples of gene interactions that result in ratios other than the expected 9:3:3:1 ratio for dihybrid crosses. These include complementary gene action between two enzymes that produce a product, duplicate gene action where two genes encode redundant enzymes, and different forms of epistasis where one gene is masked by the other. Specific examples discussed include interactions governing pigment production in fruit flies and comb morphology in chickens.
El documento resume los diferentes tipos de interacción génica (epistasis) que pueden ocurrir entre dos genes no alélicos al determinar un fenotipo. Describe seis formas de epistasis dominante, recesiva y de dominancia invertida, ilustrando cada una con ejemplos de características en plantas y animales. También discute la herencia poligénica donde múltiples genes con efectos acumulativos determinan características cuantitativas que varían en un continuo de fenotipos.
The document discusses various genetic concepts including gene interactions, dominance, codominance, incomplete dominance, lethal alleles, sex-influenced traits, penetrance, expressivity, environmental influences, pleiotropy, epistasis, and uses examples like flower color in plants and coat color in animals to illustrate these concepts. It explains that epistasis occurs when an allele of one gene masks the expression of alleles at another gene locus and defines different types of epistatic interactions like dominant epistasis and recessive epistasis.
La interacción génica epistática ocurre cuando un gen enmascara el efecto de otro gen en un locus diferente, alterando las proporciones mendelianas esperadas. Por ejemplo, en los perros labradores, el gen recesivo e enmascara la expresión de los alelos de color en el primer locus, dando como resultado 9 negros, 3 marrones y 4 amarillos. Otro ejemplo es la interacción entre los loci que determinan el color del zapallo, donde el alelo dominante W enmascara la expresión del segundo locus, dando como resultado 12
The document discusses different types of epistatic interactions, including dominant and recessive epistasis where one gene hides the effects of another gene. It provides examples of different epistatic ratios seen in traits like eye color in Drosophila and fruit shape in plants. The types of epistasis covered include dominant, recessive, duplicate recessive genes, and genes with cumulative effects.
1. The document discusses gene interactions and how they can modify Mendelian ratios by altering phenotypic expression. It provides examples of different types of epistatic interactions like complementary, duplicate, dominant, and recessive gene interactions.
2. It also covers complementation analysis, which is used to determine if two mutations causing the same phenotype are in the same or different genes. If the mutations complement, producing wild-type offspring, they are in different genes, while failure to complement means they are in the same gene.
3. The functional consequences of mutations are described as either loss-of-function, reducing or eliminating gene activity, or gain-of-function, conferring new or enhanced activity. Specific types
Genetic variation arises from four main sources: mutations, sexual reproduction, fertilization, and environmental influences. Mutations are changes in DNA that create new alleles and variations. Sexual reproduction and meiosis increase variation through independent assortment, crossing over, and random fertilization. A dihybrid cross examines inheritance of two traits controlled by separate genes. Mendel's dihybrid crosses on peas produced offspring in a 9:3:3:1 ratio, showing traits assort independently. Genetic variation allows populations to adapt to environmental changes over generations.
This document discusses different types of gene interaction, including allelic and non-allelic interaction. Allelic interaction includes complete dominance, incomplete dominance, and co-dominance. Non-allelic interaction includes complementary gene interaction, dominant and recessive epistasis, inhibitory gene interaction, and duplicate gene interaction. Examples are provided for each type of interaction, such as flower color in snapdragons and blood types in humans. Gene interaction occurs when the expression of one gene is influenced by one or more other genes.
INTRODUCTION TO GENETICS AND PRINCIPLES OF BREEDING_final.pptSenyongaEmmanuel
Introduction to Genetics:
Definition and significance of genetics.
Historical milestones in the field of genetics.
Central Dogma of Molecular Biology:
DNA replication.
Transcription and RNA synthesis.
Translation and protein synthesis.
Genetic Material:
Structure of DNA and RNA.
Genetic code and codons.
Mendelian Genetics:
Principles of inheritance (laws of segregation and independent assortment).
Punnett squares and genetic crosses.
Terms: genotype, phenotype, homozygous, heterozygous.
Non-Mendelian Inheritance:
Incomplete dominance.
Codominance.
Polygenic inheritance.
Chromosomes and Cell Division:
Overview of mitosis and meiosis.
Chromosome structure and organization.
Sex chromosomes and sex determination.
Genetic Variation:
Mutation types (point mutations, insertions, deletions).
Causes of mutations (chemical, radiation, genetic).
Genetic Disorders:
Single gene disorders (e.g., cystic fibrosis, sickle cell anemia).
Chromosomal disorders (e.g., Down syndrome, Turner syndrome).
Multifactorial disorders and gene-environment interactions.
Human Genome Project:
Purpose and goals.
Achievements and implications for medicine.
Molecular Genetics:
DNA sequencing techniques.
Recombinant DNA technology and genetic engineering.
Genetic Counseling and Testing:
Purpose and process of genetic counseling.
This document discusses extensions of Mendelian genetics including incomplete dominance, codominance, multiple alleles, and gene interactions. It provides examples of incomplete dominance in flowers where the heterozygote has an intermediate phenotype. Codominance is explained using blood types where both alleles are expressed in the heterozygote. Multiple alleles are exemplified by the ABO blood group system which has three alleles. Gene interactions like epistasis can alter expected phenotypes when genes act together.
Gregor Mendel conducted experiments with pea plants between 1856-1863. He found that when he cross-pollinated pea plants with distinct traits, the offspring displayed only one of the parental traits, and this trait was passed down predictably in future generations. His experiments demonstrated that traits are passed from parents to offspring through discrete units of inheritance, now known as genes, and established the fundamental principles of genetics including dominance, segregation of alleles, and independent assortment. Mendel's work formed the foundation of classical genetics.
Chromosomal and gene mutations can both cause changes to an organism's genetic code. Chromosomal mutations, also called genome mutations, involve changes to the structure or number of chromosomes, such as deletions, duplications, inversions, or changes in ploidy. Gene mutations involve changes to the DNA sequence of individual genes, such as point mutations, frameshift mutations, or mutations that change the resulting protein. Both types of mutations can be spontaneous or induced, and can have effects ranging from silent to lethal depending on the genes and chromosomes involved.
This document discusses genetics and evolution. It provides background on heredity, variation, Mendel's experiments with pea plants, and his laws of inheritance. It describes how traits are passed from parents to offspring through genes, alleles, dominance, and segregation. It discusses evidence for evolution, including homologous and vestigial structures, as well as theories like natural selection and genetic drift. The document also covers modern concepts like DNA, chromosomes, mutation, and molecular evidence supporting common descent.
This document provides an overview of genetics and inheritance concepts including:
- Mendel discovered the basic principles of heredity through pea plant experiments including dominant and recessive traits.
- Genetic crosses can be used to determine the likelihood of offspring inheriting certain traits based on the parents' genotypes.
- Additional concepts covered include independent assortment, polygenic inheritance, sex determination, and sex-linked inheritance.
This document provides an overview of genetics and inheritance concepts including:
- Mendel discovered the basic principles of heredity through pea plant experiments and developed the laws of segregation and independent assortment.
- Genetic crosses can be used to determine the possible outcomes and traits of offspring. Monohybrid and dihybrid crosses examine one or two trait pairs.
- Genes exist in alleles that are dominant or recessive and determine an organism's genotype and phenotype. Sex is determined by X and Y chromosomes.
The document provides information on several biology topics in a series of sections:
1. It describes the cell cycle phases of interphase, mitosis, and cytokinesis.
2. It explains protein synthesis as the process of transcription of DNA to mRNA in the nucleus, and translation of mRNA to proteins in the cytoplasm.
3. It defines DNA replication as making an exact copy of DNA during S phase by unzipping and adding complementary bases.
This document provides information about genetics and Mendelian inheritance. It begins with an introduction to important figures in the history of genetics like Gregor Mendel. It then discusses the three main theories of inheritance pre-Mendel and the history of genetics including Mendel's experiments and laws of inheritance. The rest of the document details various genetics concepts like linkage, crossing over, aneuploidy and their relationships to chromosomes and inheritance patterns.
Crop improvement can be achieved through both sexual and asexual reproduction. Sexual reproduction combines genes from two parents, creating new combinations, while asexual reproduction clones the parent plant. Vegetative propagation methods include cuttings, grafting, and tissue culture. Genetic engineering allows for direct transfer of genes between organisms. Traditional breeding techniques also improve crops through selection of desirable traits over generations. [/SUMMARY]
1. Morgan's experiments with Drosophila showed that genes located close together on the same chromosome (linked genes) tend to be inherited together more often than expected by Mendel's law of independent assortment.
2. Crossing over during meiosis can lead to new combinations of linked genes, with the frequency of crossing over determining how far apart genes are on the genetic map.
3. Sturtevant used recombination frequencies between traits to construct the first genetic map, with map units called centimorgans representing a 1% chance of crossing over.
KEY CONCEPTS
14.1 Mendel used the scientific approach to identify two laws of inheritance
14.2 Probability laws govern Mendelian inheritance
14.3 Inheritance patterns are often more complex than predicted by simple Mendelian genetics
14.4 Many human traits follow Mendelian patterns of
inheritance
Mendel's laws of segregation and independent assortment govern inheritance. When crossing two heterozygotes with different alleles at the same locus, DaDb and DcDd, the alleles will segregate and assort independently. This results in offspring genotypes in a 1:2:1:2:1:2:1:1 ratio.
Mendel's laws of segregation and independent assortment govern inheritance patterns. When Mendel crossed two heterozygotes with different alleles at the same locus (DaDb x DcDd), he would expect the following genotype proportions in the offspring:
1) 9% DaDa, DbDb, DcDc, DdDd (homozygotes)
2) 24% DaDb, DaDc, DaDd, DbDc, DbDd, DcDd (heterozygotes)
3) 43% DaDc, DaDd, DbDc, DbDd (other heterozygotes)
The alleles assort independently during gamete formation, allowing for all possible combinations in a 9:
The accountant provided tax advice to a client on December 1, 20X3 but would not be paid until January 15, 20X4. Under accrual accounting, the accountant should record the revenue in 20X3 because accrual accounting records revenue in the period the service is provided, regardless of when payment is received. Accrual accounting attempts to record the financial effects of transactions in the period they occur rather than when cash is exchanged.
This document provides an introduction to accounting. It defines accounting as a discipline that measures and communicates financial information about a business. It explains the accounting equation, the four core financial statements, and how to analyze business transactions by determining their impact on the accounting equation and each financial statement. Several examples of transaction analysis are provided and summarized.
This document outlines the topics to be covered in a biochemistry course taught by Professor Jim Roesser. The course will discuss the importance of biochemistry in fields like agriculture, medicine, history and forensic science. It will also examine the composition and interactions of biological macromolecules like proteins, nucleic acids, carbohydrates and lipids, and how they carry out functions within living organisms. Students will learn about figures and tables illustrating key concepts like biomolecular structure, interaction and recognition.
Gas chromatography is a technique used to separate and analyze mixtures that rely on differences in volatility and affinity of compounds for a mobile and stationary phase. The key components of a gas chromatography system are a carrier gas, sample injection system, column, and detector. Factors like carrier gas type, column temperature, length, diameter, and stationary phase influence separation of compounds on the column. Common detectors include thermal conductivity, flame ionization, and electron capture detectors which have different properties in terms of sensitivity, selectivity, and response characteristics.
This document discusses liquid chromatography techniques. It describes liquid chromatography as using a liquid mobile phase and liquid or solid stationary phase. It then summarizes classical liquid chromatography and high performance liquid chromatography. High performance liquid chromatography uses smaller particle sizes in the stationary phase, stronger pumps, and detectors to allow for faster separations and better resolution compared to classical liquid chromatography. The document outlines the basic components of an HPLC system including the solvent delivery system, pump, injection port, analytical column, and various detector types. It also discusses different modes of liquid chromatography like normal phase and reverse phase.
This document provides an introduction and overview of chromatography. It discusses how chromatography separates a complex mixture into individual components based on interactions between a mobile and stationary phase. Different types of chromatography are described based on variations in the stationary and mobile phases used, including gas chromatography (GC), liquid chromatography (LC), high performance liquid chromatography (HPLC), thin layer chromatography (TLC), supercritical fluid chromatography (SFC), ion chromatography (IC), size exclusion, capillary zone electrophoresis (CZE), and affinity chromatography. Key terms used to describe chromatographic separations such as retention time, capacity factor, selectivity factor, resolution, number of theoretical plates, and plate height are also defined.
1) Solvent extraction is a technique used to separate components in a mixture based on differences in solubility between two immiscible liquid phases.
2) It involves transferring a solute from one liquid phase to another, such as transferring a compound from an aqueous phase to an organic phase like benzene.
3) The amount of solute extracted into each phase can be calculated using the partition coefficient K, which is a ratio of concentrations in the two phases at equilibrium.
Atomic spectroscopy is used for qualitative and quantitative elemental analysis. It involves converting a sample into atoms, exciting the atoms, and measuring their absorption or emission of light. There are three main types of atomic spectroscopy: absorption, emission, and fluorescence spectroscopy. Samples are atomized using different heat sources like flames, furnaces, or plasma which convert the sample into gas phase atoms. The temperature of the heat source impacts the population of atoms in ground, excited, and ionized states. Instrumentation includes an atomization source, sample cell, monochromator, and detector. Detection limits range from parts-per-million to parts-per-trillion depending on the element and method used.
This document summarizes the major components of instrumentation used in absorption and emission spectroscopy experiments. It discusses common light sources, wavelength selectors like monochromators and filters, sample containers, detectors such as phototubes and photodiode arrays, and examples of single beam and double beam spectrophotometers. Key components are the light source, wavelength selector to produce monochromatic radiation, sample holder, and detector to measure the detectable output over the wavelength region of interest.
Spectroscopy involves the interaction of electromagnetic radiation with matter. Spectroscopic methods are used to elucidate molecular structure and quantify inorganic and organic compounds. There are several regions of the electromagnetic spectrum used including X-ray, UV, visible, and IR. Important concepts include Beer's law, which states absorbance is proportional to concentration, molar absorptivity, and path length. Spectrophotometry is used for qualitative and quantitative analysis in areas such as determining unknown concentrations. Fluorescence also provides a sensitive technique where molecules emit light at longer wavelengths after absorbing radiation.
This document discusses redox titration methods. It describes the Winkler method for determining dissolved oxygen in waste water and determining whether bacteria present are aerobic or anaerobic. The Karl Fischer method for determining water content is also outlined, using iodine, sulfur dioxide, and pyridine dissolved in methanol to quantitatively reduce iodine in the presence of water. Common oxidizing agents used in redox titrations include potassium permanganate, potassium bromate, cerium(IV), and potassium dichromate. Sodium thiosulfate is also described as a moderately strong standard reducing agent often used in indirect iodometric titrations to determine oxidizing agents.
This document provides an overview of electrochemistry concepts including oxidation-reduction reactions, oxidation numbers, balancing redox equations, and electrochemical cells. Key points are:
- Galvanic cells produce electrical energy from spontaneous redox reactions while electrolytic cells use electrical energy to drive non-spontaneous reactions.
- The standard cell potential (E°cell) is equal to the cathode potential minus the anode potential. All reactions must be written as reduction reactions.
- The Nernst equation relates cell potential to concentration and allows calculation of equilibrium constants.
- Memorable equations include ΔG° = -nFE° and E°cell = E°cathode - E°anode.
This document discusses experimental error in physical measurements. Every measurement has some degree of uncertainty. There are two main types of error - systematic errors which have an assignable cause and tend to be consistent in one direction, and random errors which are natural and unpredictable. Accuracy refers to how close a measurement is to the true value, while precision refers to the reproducibility of measurements. Proper evaluation of errors involves repetition of measurements, use of different methods, and statistical analysis to determine confidence intervals around results and identify outliers.
Here are the steps to solve this problem:
1) Volume of Ag+ solution = 25 mL
Moles of Ag+ = (0.0100 M) * (0.025 L) = 2.5 x 10-5 moles
2) Volume of EDTA solution = 15 mL
Moles of EDTA = (0.0200 M) * (0.015 L) = 3.0 x 10-5 moles
3) Ratio of Ag+ to EDTA is 1:1
Moles of AgEDTA formed = Minimum(Moles Ag+, Moles EDTA) = 2.5 x 10-5 moles
4) Kf' = α * Kf
* HCl is a strong acid and will titrate first
* Its equivalence point was at 35.00 mL of NaOH
* NaOH concentration is 0.100 M
* Moles of NaOH used = Volume x Concentration
= 0.03500 L x 0.100 mol/L = 0.003500 mol
* Moles of HCl = Moles of NaOH used = 0.003500 mol
* H3PO4 is a weak acid and will titrate second
* Its equivalence point was at 50.00 mL of NaOH
* Additional NaOH used = 50.00 mL - 35.00 mL = 15.00 mL
* Moles of additional Na
The document discusses different types of titrations including acid-base, oxidation-reduction, complex formation, and precipitation reactions. It defines key terms like indicator, equivalence point, and endpoint. Examples are provided for calculating concentration using titration data from reactions like acid-base titrations for chloride in urine and carbon monoxide determination. Steps are outlined for the Kjeldahl method to determine nitrogen content through acid digestion and titration.
This document discusses complex equilibrium in aqueous solutions involving multiple interacting species. It provides three examples of situations that can affect equilibrium: (1) when the solute interacts with itself or other species; (2) when the equilibrium constant is very small, requiring consideration of solvent contribution; and (3) in very dilute solutions where the solvent contribution is significant. Specific examples are worked through demonstrating how coupled equilibria and presence of other species can increase or decrease solubility compared to calculations considering only the main equilibrium reaction.
This document discusses how activity coefficients can explain the effect of inert salts on solubility and acid dissociation constants. It provides examples showing that a precipitate is more soluble and a weak acid dissociates more when the ionic strength is increased by adding an inert salt. This is because the activity coefficients of the ions are less than 1 and decrease with increasing ionic strength, making the activities higher than concentrations. The Debye-Huckel equation can be used to calculate activity coefficients based on ionic charge and strength.
This document provides information about the Quantitative Analysis (CHEM 309) course including the instructor, textbook, grade breakdown, class objectives, and chapter overview. The grade is based on tests (70%), final (20%), and homework (10%). Students are expected to attend every class, participate daily with a clicker, and complete homework each night. The course covers topics like acid-base chemistry, analytical techniques, chemical measurements, and error analysis. Concentration units like molarity, formality, molality, and ppm/ppb are also discussed.
2. 4.3 Gene Interaction Modifies Mendelian
Ratios
• Genes work together to build the complex
structures and organ systems of plants and
animals
• The collaboration of multiple genes in the
production of a single phenotypic characteristic or
group of related characteristics is termed gene
interaction
3. Representing Alleles
• Geneticists use a variety of symbols for alleles
• Dominant alleles:
– an italic uppercase letter (D) or
– letters (Wr)
– an italic letter or group of letters with the + superscript (Wr+)
• Recessive alleles:
– an italic lowercase letter (d) or
– an italic letter or group of letters (Wr)
Note that the mutant
Note that the mutant
usually gets the
usually gets the
letter name!
letter name!
s / sm / Sm
S / Sm / Sm+
4. Representing alleles in Drosophila
• Example: body color
– Ebony mutant phenotype is indicated by e
– Normal gray (wild-type) is indicated by e+
• e+/e+: gray homozygote (wild type)
• e+/e: gray heterozygote (wild type)
• e/e: ebony homozygote (mutant)
OR
• +/+: gray homozygote (wild type)
• +/e: gray heterozygote (wild type)
• e/e: ebony homozygote (mutant)
5. Gene Interaction in Pathways
• Single-gene trait describes an inherited
variation of a gene that can produce a mutant
phenotype
• However, this is not a complete depiction of
genetic reality
• Numerous genes contribute to the normal red
eye color of Drosophila, including those
responsible for production of eye pigments or
transport proteins
6. Three Genes Involved in
Drosophila Eye Color
•
The brown gene
produces an enzyme in
a pathway that
synthesizes a bright red
vermilion pigment;
mutant flies, bb, have
brown eyes
•
Note: gene named after
the mutant, not the gene
it encodes for!
•
The vermillion genes
produces an enzyme in
a pathway that
synthesizes a brown
pigment; mutant flies, vv,
have bright red eyes
•
The white gene encodes
a transporter that carries
pigment to the eye; flies
that do not produce this
protein have white eyes
7. Three Distinct Types of Genetic Pathways
• Biosynthetic pathways are
networks of interacting genes
that produce a molecular
compound as their endpoint
• Signal transduction pathways
receive chemical signals from
outside a cell and initiate a
response inside the cell
• Developmental pathways direct
growth, development and
differentiation of body parts and
structures
8. Biosynthetic Pathways…
HOW DO GENES CONTROL
BIOSYNTHETIC PATHWAYS?
HOW DO WE FIND A GENE
THAT AFFECTS A CERTAIN
PATHWAY?
9. The One-Gene-One Enzyme Hypothesis
• George Beadle and Edward
Tatum were among the first to
investigate biosynthetic
pathways
• They studied growth variants of
the fungus, Neurospora crassa
• Their proposal, the one-geneone enzyme hypothesis came
out of their experiments
Red Bread Mold; http://www.biosci.missouri.edu/shiu/
10. Beadle and Tatum Experiment
Prototroph: an
organism that can
synthesize all of its
amino acids
Auxotroph: an
organism that has lost
the ability to
synthesize certain
substances required
for its growth and
metabolism
This experiment
looked at amino acids,
but you could look at
other synthetic
pathways!
CAUSING
MUTATION!
11. The Hypothesis Made a Connection
Between Genes, Proteins and Phenotypes
• Each gene produces
an enzyme
• Each enzyme has a
specific role in a
biosynthetic pathway
that produces the
phenotype
• Each mutant
phenotype due to
the loss or
malfunction of a
specific enzyme
12. Genetic Dissection to Investigate Gene
Action
• Biosynthetic pathways consist of sequential steps
• Completion of one step generates the substrate for the next
step in the pathway
• Completion of every step is necessary to produce the end
product
• Genetic dissection is an experimental approach taken to
investigate the steps of biosynthetic pathways
13. Genetic Dissections: Horowitz’s Experiments
on Met- Mutants of Neurospora
• Horowitz’s analysis
aimed to:
• Determine the
number of
intermediate steps in
the methionine
synthesis pathway
• Determine the order
of the steps
• Identify the step
affected by each
mutation
14. Genetic Dissection: Results
of Horowitz’s Experiments
•
Whether or not a mutant strain grows on a medium containing a component of the
pathway allows determination of the step at which the mutant is blocked
•
Mutation of an enzyme will cause the pathway to become blocked.
•
If we give an intermediate from before the block, we can’t pass the block and the mutant will not grow.
•
If we give an intermediate after the block, the mutant will grow.
•
The blocked step is also identified by the substance that accumulates in the
auxotroph
•
Imagine one mutant:
Give A, B or C: Won’t grow!
X
Give D, E or F: Will grow!
What Accumulates?
15. 1. Met 1: only on minimal media + methionine, indicating it is the
last step of the pathway. Need to add methionine to get past the
block
2. Met 2: need minimal + homocysteine , therefore block is at step
that produces homocysteine. This result also tell us that
homocysteine is the substrate converted to methionine in the
biosynthetic pathway.
3. Met 3: grows on minimal, homocysteine &
cystathionine. This tells us that Met 3 is
blocked at the step that produces
cystathionine and that cystathionine
precedes homocysteine
4. Met 4 grows with any supplementation of
minimal media. This tells us that Met 4 is
defective at a step that precedes the
production of cysteine.
16. More Recent Adjustments to the Hypothesis
• Hypothesis confirmed!: Each gene produces an
enzyme
• Each enzyme has a specific role in a biosynthetic
pathway that produces the phenotype
• Recent Adjustments:
• Some protein producing genes produce transport
proteins, structural or regulatory proteins, rather
than enzymes
• Some genes produce RNAs rather than proteins
• Some proteins (e.g. β-globin) must join with other
proteins to acquire a function
17. Gene Interactions
So far…
AaBb x AaBb
Crossing genotypes leads to a
phenotypic ratio
BUT, Genes do not act alone.
Now let’s look at how genes
interact to alter phenotypic
ratios….
18. Epistasis: Gene Interactions
• Epistatic interactions happen when an allele of one gene
modifies or prevents the expression of alleles at another
gene.
• Epistatic interactions often arise because two (or more)
different proteins participate in a common cellular
function
– For example, an enzymatic pathway
Colorless
precursor
Enzyme C
The recessive c allele
encodes an inactive
enzyme
Colorless
intermediate
Enzyme P
Purple
pigment
The recessive p allele
encodes an inactive
enzyme
19. No Interaction (9:3:3:1 Ratio)
• The expected 9:3:3:1 ratio is
seen in the absence of
epistasis: when the genes do
not interact to change the
expression of one another
Dihybrid cross, F2 progeny
www.integratedbreeding.net
20. No Interaction (9:3:3:1 Ratio)
• Cross involving the brown and vermillion
genes in Drosophila
• When pure-breeding brown flies (b/b;
v+/v+) are crossed to pure-breeding
vermillion flies (b+/b+; v/v), the F1 all have
wild type red eyes (b+/b; v+/v)
•
When the F1 are interbred (b+/b; v+/v x b+/b; v+/v ), the F2
are:
•
9/16 b+/-; v+/-, wild type, red eyes
•
3/16 b/b; v+/-, brown eyes
•
3/16 b+/-; v/v, vermillion eyes
•
1/16 b/b;v/v, white eyes
• The results show that the
genes are not undergoing
epistatic interaction with one
another
21. Epistatic Interactions
• A minimum of two genes are
required for epistatic
interactions; these usually
participate in the same pathway
• There are six ways epistasis
could affect the predicted
9:3:3:1 dihybrid ratio
22. Epistatic Interactions
Gene interaction alters the classic 9:3:3:1 ratio seen in the F2
Gene interaction alters the classic 9:3:3:1 ratio seen in the F2
progeny of the dihybrid cross!
progeny of the dihybrid cross!
23. Complementary Gene Interaction (9:7 Ratio)
•
Bateson and Punnett crossed two pure-breeding strains of white flowered sweet peas
•
They found all the F1 were purple flowered; the F1 x F1 cross yielded 9/16 purple and 7/16
white flowered progeny
•
They recognized that the two genes interact to produce the overall flower
color; when genes work in tandem to produce a single gene product, it
is called complementary gene interaction
24. Duplicate Gene Action (15:1 Ratio)
• The genes in a redundant system have duplicate
gene action; they encode the same product, or they
encode products that have the same effect in a
pathway or compensatory pathways
25. Dominant Gene Interaction (9:6:1 Ratio)
•
•
Plants that have dominant allele(s) for just one of either of the genes will have
round fruit and those with only recessive alleles of both genes will have long fruit
Dominant for either gene (A or B), equals one phenotype. (3+3 = 6)
26. Recessive epistasis (9:3:4)
• B and b for black and brown melanin (MC1R gene)
• E: controls deposition of pigment in hairs (TRYP1 gene)
• ee is epistatic
• Recessive epistatsis causes yellow coat color
28. Dominant Epistasis (12:3:1 Ratio)
• In dominant epistasis, a dominant allele at one locus will
mask the phenotypic expression of the alleles at a second
locus, giving a 12:3:1 ratio
• E.g. in foxglove flowers a dominant allele at one locus
restricts the deposition of pigment to a small area of the
flower
29. Dominant Suppression (13:3 Ratio)
•
•
•
In dominant suppression, a dominant allele at one locus completely
suppresses the phenotypic expression of the alleles at a second locus,
giving a 13:3 ratio
In chickens, the C allele is responsible for pigmented feathers and the c allele for white
feathers
The dominant allele of a second gene, I, can suppress the color producing effect of the C
allele, leading to white feathers in both C/- and c/c individuals
Dominant I Isuppresses dominant
Dominant suppresses dominant
pigment production
pigment production
31. 4.4 Complementation Analysis Distinguishes
Mutations in the Same Gene from Mutations
in Different Genes
•
When geneticists encounter organisms with the
same mutant phenotype, they ask two questions:
1. Do these organisms have mutations in the same
or in different genes?
2. How many genes are responsible for the
phenotypes observed?
Ex. Two botanists working with petunias both discover a white flower
Ex. Two botanists working with petunias both discover a white flower
mutation. One works in California and one works in the Netherlands.
mutation. One works in California and one works in the Netherlands.
Are the mutations in the same genes?
Are the mutations in the same genes?
32. We have two Drosophila with the same
phenotypic mutation….
HOW DO WE KNOW IF THE
GENETIC MUTATION IS THE
SAME?
33. Genetic Complementation
Analysis
A
B
• Genetic heterogeneity is when
mutations in different genes can
produce the same or very similar
mutant phenotypes
• Mating of two organisms with similar
mutant phenotypes can lead to wild
type offspring, a phenomenon called
genetic complementation
• Complementation testing is when two
pure breeding organisms with similar
mutant phenotypes are mated
• If complementation occurs, wild type
offspring are obtained and the
mutations are known to affect two
different genes
• When the mutations fail to
complement, the offspring have the
mutant phenotype and the mutations
are known to affect the same gene
Example of a complementation test.
Two strains of flies are white eyed because of two different
autosomal recessive mutations which interrupt different steps
in a single pigment-producing metabolic pathway.
34. Complementation Analysis
• In complementation analysis
multiple crosses are performed
among numerous pure breeding
mutants to try to determine how
many different genes contribute
to a phenotype
• Mutations that mutually fail to
complement one another are
called a complementation
group
• Can’t get back to wild-type!
• Mutation is on the same gene!
• A complementation group in this
context refers to a gene
36. + = cross of pure-breeding mutants yield wild-type (complements)
+ = cross of pure-breeding mutants yield wild-type (complements)
--= cross of pure-breeding mutants yields only mutant progeny
= cross of pure-breeding mutants yields only mutant progeny
-Mutations that fail to complement each other are on the same gene
-Complementation group: consist of one or mutants of a single gene
37. There are SO many different eye colors for Drosophila!
WHAT ARE THE FUNCTIONAL
CONSEQUENCES OF
MUTATION?
38. Functional Consequences of Mutation
(See Fig. 4.1)
• A wild type phenotype is produced when an organism has
two copies of the wild type allele
• Mutant alleles can be:
• Gain-of-function, in which the gene product acquires a
new function or express increased wild type activity
• Loss-of-function, in which there is a significant
decrease or complete loss of functional gene product
40. Dominant Negative Mutations
• Multimeric proteins, composed of two or more polypeptides
that join together to form a functional protein are particularly
subject to dominant negative mutations
• These are negative mutations due to their “spoiler” effect on
the protein as a whole