Linkage and crossing over are genetic phenomena that occur during meiosis. Linkage refers to genes staying together on the same chromosome through generations without separating. Crossing over involves the exchange of genetic material between homologous chromosomes, resulting in new combinations of genes. It occurs during prophase I of meiosis and leads to variability that is important for evolution. Both linkage and crossing over are significant for inheritance and breeding.
Introduction, Types-somatic and germinal; Mechanism of meiotic crossing oversynapsis, duplication of chromosomes, breakage and union, terminalization;
Cytological basis of crossing over - Stern’s experiment in Drosophila; Creighton
and McClintock’s experiment in Maize; Crossing over in Drosophila, Construction
of genetic maps in Drosophila - two point and three-point crosses; Interference and
coincidence.
Linkage and crossing over , discovery of linked genes,types of crossing over,significance and difference between linkage and crossing over, complete presentation with suitable examples and figures
This document discusses genetic linkage and crossing over. It explains that genes located close together on the same chromosome are linked and tend to be inherited together, while genes on different chromosomes assort independently. Crossing over occurs when homologous chromosomes exchange segments during meiosis, resulting in new combinations of linked genes and the production of both parental and recombinant gametes. The frequency of crossing over between two genes decreases as they are located closer together on a chromosome.
Genetic linkage refers to genes that are located close together on the same chromosome tending to be inherited together. Crossing over can break genetic linkage during meiosis by exchanging DNA between homologous chromosomes, producing recombinant gametes with new combinations of genes. The closer genes are on a chromosome, the less likely they are to be separated by crossing over. Crossing over increases genetic variation and plays an important role in plant and animal breeding.
Linkage and crossing over are genetic phenomena that occur during meiosis. Linkage refers to genes staying together on the same chromosome through generations without separating. Crossing over involves the exchange of genetic material between homologous chromosomes, resulting in new combinations of genes. It occurs during prophase I of meiosis and leads to variability that is important for evolution. Both linkage and crossing over are significant for inheritance and breeding.
Introduction, Types-somatic and germinal; Mechanism of meiotic crossing oversynapsis, duplication of chromosomes, breakage and union, terminalization;
Cytological basis of crossing over - Stern’s experiment in Drosophila; Creighton
and McClintock’s experiment in Maize; Crossing over in Drosophila, Construction
of genetic maps in Drosophila - two point and three-point crosses; Interference and
coincidence.
Linkage and crossing over , discovery of linked genes,types of crossing over,significance and difference between linkage and crossing over, complete presentation with suitable examples and figures
This document discusses genetic linkage and crossing over. It explains that genes located close together on the same chromosome are linked and tend to be inherited together, while genes on different chromosomes assort independently. Crossing over occurs when homologous chromosomes exchange segments during meiosis, resulting in new combinations of linked genes and the production of both parental and recombinant gametes. The frequency of crossing over between two genes decreases as they are located closer together on a chromosome.
Genetic linkage refers to genes that are located close together on the same chromosome tending to be inherited together. Crossing over can break genetic linkage during meiosis by exchanging DNA between homologous chromosomes, producing recombinant gametes with new combinations of genes. The closer genes are on a chromosome, the less likely they are to be separated by crossing over. Crossing over increases genetic variation and plays an important role in plant and animal breeding.
_Genetic linkage and Crossing Over GP 102.pptxISHUJANGRA3
Genetic linkage refers to the tendency of genes located near each other on the same chromosome to be inherited together. Crossing over can break genetic linkage during meiosis by exchanging chromosomal segments between homologous chromosomes, producing new combinations of genes and generating genetic variation. A study on sweet peas found that flower color and pollen shape did not assort independently as expected, providing evidence of genetic linkage between these traits.
The document discusses the discovery of genetic linkage and crossing over. It notes that Morgan discovered that genes are located linearly on chromosomes. Linkage occurs when genes located on the same chromosome tend to be inherited together. There are two types of linkage: complete and incomplete. Incomplete linkage occurs when genes are far apart on a chromosome and can be separated during meiosis due to crossing over, where segments are exchanged between homologous non-sister chromatids. Crossing over increases with physical distance between genes and allows the construction of genetic maps.
This document discusses meiosis and genetic linkage in plants and animals. It provides details on:
- The alternation of generations life cycle in plants, which involves a diploid sporophyte and haploid gametophyte stage.
- How crossing over during meiosis increases genetic variation by exchanging parts of homologous chromosomes.
- How the frequency of recombination between two genes indicates their distance on the same chromosome, and is used to construct genetic linkage maps.
This document discusses genetic linkage and mapping techniques in eukaryotes. It defines linkage as genes failing to assort independently due to being located near each other on the same chromosome. Morgan's experiments with Drosophila showed that alleles can be inherited together or recombine during meiosis. The frequency of recombination between two linked genes provides their genetic distance in centimorgans on a linkage map. Techniques for mapping genes include testcrosses, estimating recombination frequencies in two-point and three-point crosses, and correcting for double crossovers.
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.
Principles of inheritance & Variation-IVChethan Kumar
The topic of discussion here is about Mutation & different types of mutation in organism, their effects & Mutational theory of evolution. Further the changes in the Number of chromosomes due to mutation and its effects & Mendelian disorders & their patterns of inheritance including the numerical abberations in chromosomes & the disorders associated with it.
Crossing over occurs during meiosis when non-sister chromatids of homologous chromosomes exchange genetic material. It generates genetic diversity within populations that can drive evolution. The key steps are synapsis where homologs pair, duplication, exchange of segments between chromatids at chiasmata, and separation. Factors like distance, sex, temperature, chemicals, and radiation can influence crossing over rates. Significance includes proving linear gene arrangement, producing new combinations for evolution, and enabling genetic maps.
This document discusses multiple chromosome interchanges and their use in plant breeding. It begins by defining interchanges as structural changes where non-homologous chromosome segments are exchanged. Interchanges can cause changes in linkage and chromosome behavior. The document then provides examples of naturally occurring interchanges in various plant species like Oenothera lamarckiana. It describes how interchanges can lead to semisterility and discusses different gamete types produced. It focuses on complex interchange systems in Oenothera that maintain permanent hybridity through mechanisms like balanced lethals and gametic lethals. The document concludes by outlining Burnham's method for using multiple interchanges to produce homozygous inbred lines through gamete selection.
Chromosome pairing refers to the alignment of homologous chromosomes during meiosis. In most sexually reproducing organisms, chromosomes come in pairs with one set from each parent. For cells to have a single set of chromosomes, the paired sets must separate into different daughter cells during meiosis. Pairing involves the close alignment of homologous chromosomes, usually via a protein structure called the synaptonemal complex. There are three main types of chromosome pairing: primary pairing between genetically homologous regions, secondary association between genetically similar chromosome groups, and non-homologous association between heterochromatic or euchromatic segments.
Chromosomal crossover, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes.
Meiosis is a cell division process that produces gametes (sex cells) with half the number of chromosomes. During meiosis, homologous chromosomes pair up and may exchange DNA segments through a process called crossing over. Crossing over increases genetic diversity and helps ensure balanced distribution of chromosomes in gametes. It occurs during prophase I through the formation of chiasmata between nonsister chromatids. Crossing over plays an important role in evolution by allowing independent assortment of genetic variants on chromosomes.
This document discusses various types of chromosomal mutations and aberrations. It describes two main types - changes in chromosome structure, which includes deletions, duplications, inversions, and translocations, and changes in chromosome number, such as aneuploidy (gaining or losing a chromosome) and euploidy (gaining or losing a full set of chromosomes). Specific examples of each type of structural change and number change are provided, along with their genetic effects and examples in humans and other organisms.
1. Linkage occurs when genes located on the same chromosome fail to assort independently during meiosis. This causes traits to be inherited together in offspring.
2. Bateson and Punnett first reported linkage in 1906 while studying flower color and pollen shape in peas. They observed a deviation from expected Mendelian ratios, indicating linkage between the genes.
3. Morgan's studies of fruit flies provided the first evidence that linkage is due to genes being located on the same chromosome. Crossing over during meiosis can lead to new combinations of linked genes.
Linkage and Crossing over (Sanjay Chetry).pptxsanjaychetry2
Linkage
1. Linkage ensures to keep the genes in a chromosome to inherit together
2. The strength of linkage between two genes is inversely proportional to the distance between them in the chromosome
3. The strength of linkage between two genes increases with the decrease in distance between them.
4. The strength of linkage decrease with increase in distance between the genes.
5. Linkage ensures the maintenance of parental trait in the offspring.
6. Linkage reduces the chance of creation of variability with sexual reproduction.
Crossing Over
1. Crossing over facilitates the separation of genes present chromosome and segregate into different gametes.
2. The chance of crossing over between two genes is directly proportional to the distance between them in the chromosome
3. The chance of crossing over between two genes decreases with the decrease in the distance between them.
4. The chance of crossing increases with increase in distance between the genes.
5. The crossing over causes alterations in the parental traits in the offspring.
6. Crossing over increases the chance of variability with sexual reproduction.
Crossing over and Recombination in Meiosos.pdfSamonteKim
Crossing over occurs during meiosis when segments are exchanged between non-sister chromatids of homologous chromosomes, resulting in recombinant chromosomes. There are two main theories for the origin of crossing over: 1) it evolved as a method of DNA repair or 2) it evolved from bacterial transformation to propagate diversity. The major steps of meiotic crossing over are synapsis, chromosome duplication, crossing over itself, and terminalization. Crossing over increases genetic variation between offspring and parents, ensuring individuals do not look exactly alike.
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.
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.
Chromosomal aberrations arise from structural changes or alterations in chromosome number. There are two main types of chromosomal aberrations: structural aberrations which involve changes in chromosome structure, and numerical aberrations which involve changes in chromosome number. Common types of structural aberrations discussed in the document include deletions, duplications, inversions, and translocations. Deletions involve the loss of a chromosome segment, duplications the addition of an extra segment, inversions reverse the orientation of a segment, and translocations involve segments moving to new chromosomes. These structural changes can have varying genetic effects depending on the location and size of the alteration.
_Genetic linkage and Crossing Over GP 102.pptxISHUJANGRA3
Genetic linkage refers to the tendency of genes located near each other on the same chromosome to be inherited together. Crossing over can break genetic linkage during meiosis by exchanging chromosomal segments between homologous chromosomes, producing new combinations of genes and generating genetic variation. A study on sweet peas found that flower color and pollen shape did not assort independently as expected, providing evidence of genetic linkage between these traits.
The document discusses the discovery of genetic linkage and crossing over. It notes that Morgan discovered that genes are located linearly on chromosomes. Linkage occurs when genes located on the same chromosome tend to be inherited together. There are two types of linkage: complete and incomplete. Incomplete linkage occurs when genes are far apart on a chromosome and can be separated during meiosis due to crossing over, where segments are exchanged between homologous non-sister chromatids. Crossing over increases with physical distance between genes and allows the construction of genetic maps.
This document discusses meiosis and genetic linkage in plants and animals. It provides details on:
- The alternation of generations life cycle in plants, which involves a diploid sporophyte and haploid gametophyte stage.
- How crossing over during meiosis increases genetic variation by exchanging parts of homologous chromosomes.
- How the frequency of recombination between two genes indicates their distance on the same chromosome, and is used to construct genetic linkage maps.
This document discusses genetic linkage and mapping techniques in eukaryotes. It defines linkage as genes failing to assort independently due to being located near each other on the same chromosome. Morgan's experiments with Drosophila showed that alleles can be inherited together or recombine during meiosis. The frequency of recombination between two linked genes provides their genetic distance in centimorgans on a linkage map. Techniques for mapping genes include testcrosses, estimating recombination frequencies in two-point and three-point crosses, and correcting for double crossovers.
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.
Principles of inheritance & Variation-IVChethan Kumar
The topic of discussion here is about Mutation & different types of mutation in organism, their effects & Mutational theory of evolution. Further the changes in the Number of chromosomes due to mutation and its effects & Mendelian disorders & their patterns of inheritance including the numerical abberations in chromosomes & the disorders associated with it.
Crossing over occurs during meiosis when non-sister chromatids of homologous chromosomes exchange genetic material. It generates genetic diversity within populations that can drive evolution. The key steps are synapsis where homologs pair, duplication, exchange of segments between chromatids at chiasmata, and separation. Factors like distance, sex, temperature, chemicals, and radiation can influence crossing over rates. Significance includes proving linear gene arrangement, producing new combinations for evolution, and enabling genetic maps.
This document discusses multiple chromosome interchanges and their use in plant breeding. It begins by defining interchanges as structural changes where non-homologous chromosome segments are exchanged. Interchanges can cause changes in linkage and chromosome behavior. The document then provides examples of naturally occurring interchanges in various plant species like Oenothera lamarckiana. It describes how interchanges can lead to semisterility and discusses different gamete types produced. It focuses on complex interchange systems in Oenothera that maintain permanent hybridity through mechanisms like balanced lethals and gametic lethals. The document concludes by outlining Burnham's method for using multiple interchanges to produce homozygous inbred lines through gamete selection.
Chromosome pairing refers to the alignment of homologous chromosomes during meiosis. In most sexually reproducing organisms, chromosomes come in pairs with one set from each parent. For cells to have a single set of chromosomes, the paired sets must separate into different daughter cells during meiosis. Pairing involves the close alignment of homologous chromosomes, usually via a protein structure called the synaptonemal complex. There are three main types of chromosome pairing: primary pairing between genetically homologous regions, secondary association between genetically similar chromosome groups, and non-homologous association between heterochromatic or euchromatic segments.
Chromosomal crossover, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes.
Meiosis is a cell division process that produces gametes (sex cells) with half the number of chromosomes. During meiosis, homologous chromosomes pair up and may exchange DNA segments through a process called crossing over. Crossing over increases genetic diversity and helps ensure balanced distribution of chromosomes in gametes. It occurs during prophase I through the formation of chiasmata between nonsister chromatids. Crossing over plays an important role in evolution by allowing independent assortment of genetic variants on chromosomes.
This document discusses various types of chromosomal mutations and aberrations. It describes two main types - changes in chromosome structure, which includes deletions, duplications, inversions, and translocations, and changes in chromosome number, such as aneuploidy (gaining or losing a chromosome) and euploidy (gaining or losing a full set of chromosomes). Specific examples of each type of structural change and number change are provided, along with their genetic effects and examples in humans and other organisms.
1. Linkage occurs when genes located on the same chromosome fail to assort independently during meiosis. This causes traits to be inherited together in offspring.
2. Bateson and Punnett first reported linkage in 1906 while studying flower color and pollen shape in peas. They observed a deviation from expected Mendelian ratios, indicating linkage between the genes.
3. Morgan's studies of fruit flies provided the first evidence that linkage is due to genes being located on the same chromosome. Crossing over during meiosis can lead to new combinations of linked genes.
Linkage and Crossing over (Sanjay Chetry).pptxsanjaychetry2
Linkage
1. Linkage ensures to keep the genes in a chromosome to inherit together
2. The strength of linkage between two genes is inversely proportional to the distance between them in the chromosome
3. The strength of linkage between two genes increases with the decrease in distance between them.
4. The strength of linkage decrease with increase in distance between the genes.
5. Linkage ensures the maintenance of parental trait in the offspring.
6. Linkage reduces the chance of creation of variability with sexual reproduction.
Crossing Over
1. Crossing over facilitates the separation of genes present chromosome and segregate into different gametes.
2. The chance of crossing over between two genes is directly proportional to the distance between them in the chromosome
3. The chance of crossing over between two genes decreases with the decrease in the distance between them.
4. The chance of crossing increases with increase in distance between the genes.
5. The crossing over causes alterations in the parental traits in the offspring.
6. Crossing over increases the chance of variability with sexual reproduction.
Crossing over and Recombination in Meiosos.pdfSamonteKim
Crossing over occurs during meiosis when segments are exchanged between non-sister chromatids of homologous chromosomes, resulting in recombinant chromosomes. There are two main theories for the origin of crossing over: 1) it evolved as a method of DNA repair or 2) it evolved from bacterial transformation to propagate diversity. The major steps of meiotic crossing over are synapsis, chromosome duplication, crossing over itself, and terminalization. Crossing over increases genetic variation between offspring and parents, ensuring individuals do not look exactly alike.
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.
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.
Chromosomal aberrations arise from structural changes or alterations in chromosome number. There are two main types of chromosomal aberrations: structural aberrations which involve changes in chromosome structure, and numerical aberrations which involve changes in chromosome number. Common types of structural aberrations discussed in the document include deletions, duplications, inversions, and translocations. Deletions involve the loss of a chromosome segment, duplications the addition of an extra segment, inversions reverse the orientation of a segment, and translocations involve segments moving to new chromosomes. These structural changes can have varying genetic effects depending on the location and size of the alteration.
hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skills
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
ESA/ACT Science Coffee: Diego Blas - Gravitational wave detection with orbita...Advanced-Concepts-Team
Presentation in the Science Coffee of the Advanced Concepts Team of the European Space Agency on the 07.06.2024.
Speaker: Diego Blas (IFAE/ICREA)
Title: Gravitational wave detection with orbital motion of Moon and artificial
Abstract:
In this talk I will describe some recent ideas to find gravitational waves from supermassive black holes or of primordial origin by studying their secular effect on the orbital motion of the Moon or satellites that are laser ranged.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
The technology uses reclaimed CO₂ as the dyeing medium in a closed loop process. When pressurized, CO₂ becomes supercritical (SC-CO₂). In this state CO₂ has a very high solvent power, allowing the dye to dissolve easily.
2. WHAT IS LINKAGE?
• It is the tendency of genes to stay together during
inheritance through generations without any change or
separation due to their presence on the same chromosome.
3. Discovery of Linkage
• The principle of linkage was discovered by English
Scientists William Bateson and R.C. Punnet in 1906
in Sweet Pea (Lathyrus odoratus).
• It was Morgan who clearly proved and defined
linkage on the basis of his breeding experiments in
fruitfly Drosophila melanogaster.
4. Genes in Linkage
LINKED GENE
Genes located on the same chromosome
are called as Linked Genes and when
they get transmitted to the offspring their
transmission pattern is called LINKAGE.
These genes do not show independent
assortment. It occurs in same
chromosome.
Dihybrid ratio of linked gene is 3:1.
UNLINKED GENE:
Those located on separate
chromosomes are called Unlinked
Genes.
These gene show independent
assortment.
Dihybrid ratio is 9:3:3:1.
5.
6. CHARACTERISTICS OFLINKAGE
• It usually involves those genes which are located closeto each other.
• The strength of linkage depends on the distance between the linked gene.
• *Lesser the distance higher the strength of linkage*
7. EXPERIMENT
• When the F1 plants were self fertilized , Bateson
and Punnet observed a peculiar distribution of
phenotypes among the offspring.
• Instead the expected 9:3:3:1 ratio of two
independently assorted genes, they obtained a ratio
of 23 :1:1: 6.8.
• This departure from the expected mendelian
results was due to linkage between the gene for
flower color and that of pollen length .
8. KINDS OF LINKAGE
1. ON THE BASIS OF CROSSING OVER
• Complete linkage
• Incomplete linkage
2. ON THE BASIS OF CHROMOSOMES INVOLVED
• Autosomal linkage
• Allosomal Linkage
9. ON THE BASIS OFCROSSING
OVER
COMPLETE LINKAGE- 100% Parental Combination (NO Recombinants)
• The genes located on the same chromosome are inherited together over the
generations due to gamete formation and do not exhibit Mendel’s Law of
Independent Assortment.
• Then that type of linked gene is referred to as completely linked gene.
• The phenotypic ratio of F2 generation upon selfing F1 individual will be 3:1
instead of 9:3:3:1.
• Test cross ratio will be 1:1 instead of 1:1:1:1.
10.
11.
12.
13. INCOMPLETE LINKAGE
• If 100% parental combinations is not observed ie, there are some non parental
combinations called Cross Overs.
• This arises due to recombination or Crossing over.
• Such Linkage is incomplete linkage
• It follows *Mendel’s Law of Independent Assortment*.
• The Dihybrid F2 ratio will be 9:3:3:1.
• The Test cross ratio will be 1:1:1:1.
14.
15.
16. • In case of incomplete linkage 50% of progeny are with parental or non-
crossover genotypes.
• And 50% of progeny are with non-parental or crossovers , with a new
combination of alleles and produces new phenotype/genotype.
17. `
2.Based on the chromosomes involved:- Based on the location of the
genes on the chromosomes,linkage is categorized into:-
i. Autosomal linkage:- It refers to linkage of those genes which are
located in autosome (other than the sex chromosomes).
ii.Allosomal linkage:- It refers to linkage of genes which are located in sex
chromosomes i.e. either“X’or “Y’.
ON THE BASIS OF CHROMOSOMES INVOLVED
18. Linkage group
• A linkage group is a linearly arranged
group of linked genes which are normally
inherited together.
• That is, during cell division they act and
move as a unit rather than independently.
• Example:- In a fruit fly Drosophila
melanogaster has four linkage group (Four
pairs of chromosomes).
• In human being 23 linkage group are
present (23 pairs ofchromosomes).
Linkage group
19. CROSSING OVER
• Crossing over or (chromosomal
cross over) is the exchange of
genetic material between
homologous chromosomes that
results in recombinant
chromosomes
20. Discovery of crossing over
• Frans Alfons Janssens who described the
phenomenon of crossing over in 1909.
• He is observed cross-like arrangements in
meiosis and proposed crossing over as a
genetic process.
21. Characteristics of crossing over:
• Crossing over occurs between non-sister chromatids.
• One chromatid from each of the two homologues chromosomes is involved in crossing
over.
• Crossing over leads to re-combinations or new combinations between linked genes.
• The value of crossover or recombinants may vary from 0- 50%.
• Crossing over generally yields two recombinant types or crossover types and two
parental types or non-crossover types.
• Crossing over generally leads to exchange of equal segments or genes and recombination is
always reciprocal.
22.
23. Stage at which crossing over occur
• The meiotic crossing over takes
place during the pachytene stage of
the prophase of meiosis –I.
Pachytene stage is also known as
recombination stage. Crossing over
occurs when homologous
chromosomes are in the four
chromatid or tetrad stage in
pachytene.
25. 1.Synapsis (During Zygotene stage)
• In the Zygotene stage or the
pairing phase1; the homologous
chromosome of each pair come
together and line up side by
side.
• This pairing of homologous
chromosomes is called Synapsis.
26. 2. Tetrad formation
During Zygotene Stage:
The two chromatids of chromosome are referred
to as dyad.
• A group of four homologous chromatids (two
dyad) of two synapsed homologous
chromosome is known as tetrad. The two
chromatids of same chromosome are called
sister chromatids.
• The two chromatids, one of the one
chromosome and other of its homologue, are
termed non-sister chromatids.
27. 3.Synaptonemal complex
• During Zygotene stage of meiosis:
A highly organized structure of filaments is
formed between the paired homologous
chromosome at the zygotene and pachytene
stages of meiosis-I, the structure is called
synaptonemal complex.
It helps in crossing over by keeping the
homologous chromosome in closely paired
state.
28.
29. 3. Exchange of chromatid segments
• Crossing Over occurs during the Pachytene stage of Meiosis 1.
• Two non sister chromatid in a tetrad break at equivalent locations.
• The broken ends transpose and join the respective broken ends of
opposite chromatid.
• This complete the process of crossing over.
• The unchanged chromatids are called parental or non cross overs.
• The changed chromatids are called recombinants.
30. • Physical breakage of chromatids
into segments
Transposition of segments
Reunion of segments
31.
32. 4.Terminalization
• Completion of crossing over marks the end of pachytene stage and beginning of diplotene
stage.
• Synaptic forces end and the homologous chromosomes separate.
• The points at which the separation does not occur is called chiasmata.
• During the 4th stage of prophase 1,the homologous chromosomes seems to repel each other
or desynapse and for X shaped structures called CHAISMATA (Occurs during Diplotene
stage)
• The chromatids separate progressively from the centromere towards the chiasma which
moves like a zipper towards the end of tetrad.
• The slipping of chiasmata towards the ends of the bivalents is called terminalization.
33. Significance of crossing over
• The frequency of Crossing over helps in mapping of chromosomes
i.e. determining the location of genes on the chromosomes.
• It is an important factor in sexual reproduction.
• It increases the variation which is vital for evolution.
• It helps in plant breeding also.
34. Types of crossing over
It is mainly two types:
• Somatic or mitotic crossing over.(Not ususal, but found in only some
organisms.)
• Germinal or meiotic crossing over. It is furtherdivided into two types
• Equal crossing over
• Unequal crossing over
35. Somatic or mitotic crossing over
• This type of crossing over occurs in thesomatic
cells during mitosis.
• It is rare and has no genetic significance.
• Example- Curt Stern reported it in the fruitfly and
Pontecorvo noted it in the fungus Aspergillus
36. Germinal or meiotic crossing over
• This type of crossing over takes place in the germinal cells during
meiosis that produces gametes.
• It is universal and has a great genetic significance
37. Kinds of Germinal crossing over
(A)Equal crossing over :- The segments exchanged between
the chromosomes are of equal size. It is divided into three
types according to the number of points at which it occurs.
• Single crossing over
• Double crossing over
• Multiple crossing over
38. • Single crossing over In this type of
crossing over the chromatids break and
reunite at one point only.
• Double crossing over During this type
of crossing over the chromatids break
and reunite at two points in the same
tetrad.
• Multiple crossing over: In multiple
crossing over, chromatid break and
reunite at many points in the tetrad . It
occurs rarely.
39. • Unequal crossing over
The segments exchange between chromatids are unequal so that one
chromosome receives an extra gene, and other gets one gene less.
40. Difference between Linkage and Crossing over
Linkage
• It keeps the genes together.
• It involves individual chromosomes.
• It reduces variability
Crossing over
• It leads to separation of linked
genes.
• It involves exchange of segments
between non-sister chromatids of
homologous chromosome.
• It increase variability by forming
new gene combinations.
