AP Bio Ch 12 Power Point

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Patterns of Inheritance

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  • AP Bio Ch 12 Power Point

    1. 1. Patterns of Inheritance
    2. 2. Genetics <ul><li>Field founded by Gregor Mendel, monk in a monastery in Brno (now in Czech Republic) in late 1800s </li></ul><ul><li>Worked with sweet pea </li></ul><ul><li>Knew nothing of cells, chromosomes, etc.; also interested in math. </li></ul><ul><li>Was unappreciated by peers, Work was rediscovered after Charles Darwin , after Mendel’s death </li></ul>
    3. 3. Inheritance <ul><li>Inheritance is the process by which the characteristics of individuals are passed to their offspring </li></ul><ul><li>Genes encode these characteristics </li></ul><ul><li>A gene is a unit of heredity that encodes information for the form of a particular characteristic </li></ul><ul><li>The location of a gene on a chromosome is called its locus </li></ul>
    4. 4. Alleles <ul><li>Homologous chromosomes carry the same kinds of genes for the same characteristics </li></ul><ul><li>Genes for the same characteristic are found at the same loci on both homologous chromosomes </li></ul>
    5. 5. Alleles <ul><li>Genes for a characteristic found on homologous chromosomes may not be identical </li></ul><ul><li>Alternate versions or forms of genes found at the same gene locus are called alleles </li></ul>
    6. 6. Alleles <ul><li>Each cell carries two alleles per characteristic, one on each of the two homologous chromosomes </li></ul><ul><li>If both homologous chromosomes carry the same allele (gene form) at a given gene locus, the organism is homozygous at that locus </li></ul><ul><li>If two homologous chromosomes carry different alleles at a given locus, the organism is heterozygous at that locus (a hybrid ) </li></ul>
    7. 7. Genes, Alleles, Loci, and Chromosomes Chromosome from One Parent Homologous Chromosome from Other Parent M locus has gene that controls leaf color . Plant homozygous for this gene D locus has gene that controls plant height . Plant homozygous for this gene Bk locus has gene that controls fruit shape . Plant heterozygous for this gene 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Loci: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Loci:
    8. 8. The Secrets of Mendel’s Success <ul><li>Important aspects of pea plants </li></ul><ul><ul><li>Pea flowers have male structures that produce pollen (male gametes) by meiosis </li></ul></ul><ul><ul><li>Pea flowers have female structures that produce eggs (female gametes) by meiosis </li></ul></ul><ul><ul><li>Pea flower petals enclose both male and female flower parts and prevent entry of pollen from another pea plant </li></ul></ul>
    9. 9. Seeds & Flowers of Edible Pea Intact pea flower Flower dissected to show reproductive structures Stamens (male) produce pollen Carpel (female) produces eggs
    10. 10. The Secrets of Mendel’s Success <ul><li>Mendel experimental design was simple and methodical </li></ul><ul><ul><li>He studied characteristics that have unmistakably different forms (like purple versus white) </li></ul></ul><ul><ul><li>He only studied one trait (characteristic) at a time </li></ul></ul>
    11. 11. Definitions 1 <ul><li>Must know these!!! </li></ul><ul><li>Trait —A variable characteristic of organism </li></ul><ul><li>Gene —A segment of chromosomal DNA controlling a specific trait </li></ul><ul><li>Locus —Chromosomal position where DNA for a specific gene lives </li></ul><ul><li>Genome —Refers to all standard loci for a species </li></ul>
    12. 12. Definitions 2 <ul><li>Must know these!!! </li></ul><ul><li>Alleles —Different forms of a gene </li></ul><ul><ul><li>“Flower color” is a gene; </li></ul></ul><ul><ul><li>“Purple” is one flower-color allele </li></ul></ul><ul><ul><li>“White” is another flower-color allele </li></ul></ul><ul><li>Genotype —List of alleles for an individual at specific genes </li></ul><ul><ul><li>Familiar organisms are diploid </li></ul></ul><ul><ul><li>One or two alleles per individual </li></ul></ul>
    13. 13. Definitions 3 <ul><li>Homozygous —Maternal & paternal alleles same </li></ul><ul><ul><li>Father donates purple-flower allele </li></ul></ul><ul><ul><li>Mother donates purple-flower allele </li></ul></ul><ul><li>Heterozygous —Maternal & paternal alleles differ </li></ul><ul><ul><li>Father donates purple-flower allele </li></ul></ul><ul><ul><li>Mom donates white-flower allele </li></ul></ul>
    14. 14. Definitions 4 <ul><li>Phenotype : </li></ul><ul><ul><li>List of traits exhibited by individual </li></ul></ul><ul><ul><li>Doesn’t always represent genotype </li></ul></ul><ul><li>Dominant —Allele that is expressed 100% in heterozygote </li></ul><ul><li>Recessive —Allele is not expressed in heterozygote </li></ul><ul><li>Incomplete dominance —heterozygote displays intermediate trait </li></ul>
    15. 15. Genetic Symbolism <ul><li>Often use initial letter of dominant allele </li></ul><ul><ul><li>Capital letter represents dominant </li></ul></ul><ul><ul><li>Lower case of same letter represents recessive </li></ul></ul><ul><li>If purple flower dominant to white… </li></ul><ul><ul><li>“P” represents allele for purple </li></ul></ul><ul><ul><li>“p” represents allele for white </li></ul></ul>
    16. 16. Cross Fertilization of Parents True-breeding Purple-flowered Parent True-breeding White-flowered Parent Cross-Fertilize All Purple-flowered Offspring Pollen Pollen P P F 1
    17. 17. Self-fertilization of F 2 F 1 Self-Fertilize F 2 F 2 F 2 F 2 75% Purple 25% White
    18. 18. Genotype vs Phenotype <ul><li>Phenotype is how we look/behave </li></ul><ul><ul><li>Purple flowers </li></ul></ul><ul><ul><li>White flowers </li></ul></ul><ul><li>Genotype is what our genes say </li></ul><ul><ul><li>White Flowers / White Flowers </li></ul></ul><ul><ul><li>White Flowers / Purple Flowers </li></ul></ul><ul><ul><li>Purple Flowers / Purple Flowers </li></ul></ul>
    19. 19. Genotype vs Phenotype 2 <ul><li>Genotypes </li></ul><ul><ul><li>PP = homozygous for purple flower </li></ul></ul><ul><ul><li>pp = homozygous for white flower </li></ul></ul><ul><ul><li>Pp = heterozygous for flower color </li></ul></ul><ul><li>Phenotype from genotype: </li></ul><ul><ul><li>PP = purple flower </li></ul></ul><ul><ul><li>Pp = purple flower </li></ul></ul><ul><ul><li>pP = purple flower </li></ul></ul><ul><ul><li>pp = White flower </li></ul></ul>
    20. 20. How Meiosis Separates Genes <ul><li>The two alleles for a characteristic separate during gamete formation (meiosis) </li></ul><ul><ul><li>Homologous chromosomes separate in meiosis anaphase I </li></ul></ul><ul><ul><li>Each gamete receives one of each pair of homologous chromosomes and thus one of the two alleles per characteristic </li></ul></ul><ul><ul><li>The separation of alleles in meiosis is known as Mendel’s Law of Segregation </li></ul></ul>
    21. 21. Gametes of Homozygotes A A Homozygous Parent Gametes All gametes identical regarding this gene A A
    22. 22. Gametes of Heterozygotes A a Heterozygous Parent Gametes Gametes 50/50 regarding this gene A a
    23. 23. Homozygous Dominant X Homozygous Recessive pp homozygous recessive P p P p Purple Parent PP homozygous dominant White Parent sperm nuclei egg nuclei sperm nuclei egg nuclei
    24. 24. P Sperm + p Eggs same as p Sperm + P Eggs Pp pP Purple F 1 Purple F 1 P p sperm nucleus egg nucleus + p P egg nucleus sperm nucleus +
    25. 25. Pp X Pp Cross Purple homozygous dominant (PP) Purple heterozygous (Pp) Purple heterozygous (pP) White homozygous recessive (pp) P p p P p P P p + + + + F 1 Sperm F 1 Eggs F 2 Offspring
    26. 26. Using Punnett Squares in Genetic Crosses <ul><li>Named after geneticist Reginald Punnett </li></ul><ul><li>Figured using Punnett squares </li></ul><ul><ul><li>Considers only genes of interest </li></ul></ul><ul><ul><li>List sperm genotypes across top </li></ul></ul><ul><ul><li>List egg genotypes down side </li></ul></ul><ul><ul><li>Fill in boxes with zygote genotypes </li></ul></ul>
    27. 27. Consider Flower Color <ul><li>Pretend flower color affected by only one gene ( monohybrid cross ) </li></ul><ul><li>Assume all alleles are purple or white </li></ul><ul><li>Purple (P) is dominant to white (p) </li></ul><ul><li>Heterozygotes will have flowers as purple as homozygous dominants </li></ul>
    28. 28. Making a Punnett Square: Heterozygous X Heterozygous P p 1(25%) White 3 (75%) Purple Eggs of Heterozygous Plant Pollen of Heterozygous Plant 1 1 P p p P P p P P p p Frequencies Phenotypes Genotypes Frequencies 2 PP p p p P P p
    29. 29. Practical Application: The Test Cross <ul><li>A test cross is used to deduce the actual genotype of an organism with a dominant phenotype (i.e., is the organism PP or Pp ?) </li></ul><ul><ul><li>Cross the unknown dominant-phenotype organism ( P _) with a homozygous recessive organism ( pp )… </li></ul></ul>
    30. 30. Practical Application: The Test Cross <ul><ul><li>2. If the dominant-phenotype organism is homozygous dominant ( PP ), only dominant-phenotype offspring will be produced ( Pp ) </li></ul></ul><ul><ul><li>If the dominant-phenotype organism is heterozygous ( Pp ), approximately half of the offspring will be of recessive phenotype ( pp ) </li></ul></ul>
    31. 31. Test Cross: Heterozygous X Homozygous Recessive p p (50%) White (50%) Purple Eggs of Homozygous Recessive Pollen of unknown plant with dominant phenotype (Heterozygous) P p p p P p P P p p Frequencies Phenotypes Genotypes Frequencies 2 Pp p p p P p p 2
    32. 32. Test Cross: Homozygous X Homozygous Recessive p p (100%) Purple Eggs of Homozygous Recessive Pollen of unknown plant with dominant phenotype (Homozygous) P P p P p P p P p P Frequencies Phenotypes Genotypes Frequencies Pp P p P p P p 4
    33. 33. Traits of Peas Studied by Mendel Plant size Flower location Flower color Pod color Pod shape Seed shape Seed color
    34. 34. Traits Are Inherited Independently <ul><li>Seed color (yellow vs. green peas) and seed shape (smooth vs. wrinkled peas) were the characteristics studied </li></ul><ul><li>The allele symbols were assigned: </li></ul><ul><ul><li>Y = yellow (dominant), y = green (recessive) </li></ul></ul><ul><ul><li>S = smooth (dominant), s = wrinkled (recessive) </li></ul></ul><ul><li>Two trait cross was between two true breeding varieties for each characteristic </li></ul><ul><ul><li>P: SSYY x ssyy </li></ul></ul>
    35. 35. Traits Are Inherited Independently <ul><ul><li>Genes of pea color and pea shape ( S , s and Y , y ) separate independently during meiosis ( Mendel’s Law of Independent Assortment ) </li></ul></ul><ul><ul><ul><li>Possible gametes of parent SSYY are SY , SY , SY , and SY (each S can combine with each Y ) </li></ul></ul></ul><ul><ul><ul><li>Possible gametes of parent ssyy are sy , sy , sy , and sy (each s and combine with each y ) </li></ul></ul></ul>
    36. 36. Dihybrid Cross: S s Y y X S s Y y SY S y s Y sy SsYy Parent Self-fertilizes 1 4 1 4 1 4 1 4 SY S y s Y sy 1 4 1 4 1 4 1 4 Eggs Sperm 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 SSYY SSY y S s YY S s Y y SS y Y SS yy S sy Y S syy s SYY s SY y ss YY ss Y y s S y Y s S yy ssy Y ssyy
    37. 37. Traits Are Inherited Independently <ul><li>Mendel then allowed the F1 offspring to self fertilize: SsYy x SsYy </li></ul><ul><li>Gametes are ¼ S Y , ¼ Sy , ¼ sY , ¼ sy from each parent </li></ul>
    38. 38. Traits Are Inherited Independently <ul><li>4 x 4 Punnett square yields: </li></ul><ul><ul><li>9/16 smooth yellow peas </li></ul></ul><ul><ul><li>3/16 smooth green peas </li></ul></ul><ul><ul><li>3/16 wrinkled yellow peas </li></ul></ul><ul><ul><li>1/16 wrinkled green peas </li></ul></ul>
    39. 39. Independent Assortment Meiosis II Meiosis I Randomly one or the other Chromosome Replication Y S S Y y s s y y S S y Y s Y s S y y S Y Y s s S s Y y S s Y y Y y S s Y Y S s y y S s S Y Y S s y y s
    40. 40. Genes on the Same Chromosome <ul><li>Mendel’s Law of Independent Assortment only works for genes whose loci are on different chromosomes </li></ul><ul><li>Different gene loci located on the same chromosome tend to be inherited together </li></ul><ul><li>Characteristics whose genes tend to assort together are said to be linked </li></ul>
    41. 41. Linkage Red Allele, p Round Allele, l Purple Allele, P Long Allele, L Flower color gene Pollen shape gene
    42. 42. Recombination <ul><li>Genes on the same chromosome do not always sort together </li></ul><ul><li>Crossing over in Prophase I of meiosis creates new gene combinations </li></ul><ul><li>Crossing over involves the exchange of DNA between chromatids of paired homologous chromosomes in synapsis </li></ul>
    43. 43. Crossing Over red red Purple Purple round round Long Long Sister Chromatids Sister Chromatids old combination new combination new combination old combination P P p p L L l l P p p L L l l P L p L l l P p P L p L l l P p L L l l P P p p P P p p L L l l P p p L L l l Duplicated Chromosome Duplicated Chromosome L L l l P P p p Homologous Chromosomes P P p p L L l l P p p L L l l p L P l L P l p Flower Color Pollen Shape
    44. 48. Sex Chromosomes and Autosomes <ul><li>Mammals and many insect species have a set of sex chromosomes that dictate gender </li></ul><ul><ul><li>Females have two X chromosomes </li></ul></ul><ul><ul><li>Males have an X chromosome and a Y chromosome </li></ul></ul><ul><ul><li>Sex chromosomes segregate during meiosis </li></ul></ul><ul><ul><li>[The rest of the (non-sex) chromosomes are called autosomes] </li></ul></ul>
    45. 50. Sex Determination in Mammals X 1 X 2 EGGS Male Parent Y X m S P E R M Female Offspring Male Offspring Y X m X m X 1 X 2 X m Y Y X 1 X 2 X 1 X 2 Female Parent
    46. 51. Sex-Linked Genes Are on the X or the Y <ul><li>Genes carried on one sex chromosome are sex-linked </li></ul><ul><ul><li>X chromosome is much larger than the Y and carries over 1000 genes </li></ul></ul><ul><ul><li>Y chromosome is smaller and carries only 78 genes </li></ul></ul><ul><li>The X and the Y have very few genes in common </li></ul><ul><ul><li>Females (XX) can be homozygous or heterozygous for a characteristic </li></ul></ul><ul><ul><li>Males (XY) have only one copy of the genes on the X or the Y </li></ul></ul>
    47. 52. How Sex-Linkage Affects Inheritance <ul><li>Patterns of sex-linked inheritance were first discovered in fruit flies ( Drosophila ) in early 1900s </li></ul><ul><li>Eye color genes were found to be carried by the X chromosome </li></ul><ul><ul><li>R = red eyes (dominant) </li></ul></ul><ul><ul><li>r = white eyes (recessive) </li></ul></ul>
    48. 53. How Sex-Linkage Affects Inheritance <ul><li>Sex-linked (specifically X-linked ) recessive alleles displayed their phenotype more often in males </li></ul><ul><ul><li>Males showed recessive white-eyed phenotype more often than females in an </li></ul></ul><ul><ul><li>X R X r x X r Y cross </li></ul></ul><ul><li>Males do not have a second X-linked gene (as do females) which can mask a recessive gene if dominant </li></ul>
    49. 54. Sex Linkage: Eye Color in Fruit Flies 25% Normal f Carrier f Normal m 25% 25% 25% White-e m Eggs of X R X r Female Sperm of X R Y Male 1 1 Y X R X R X r X R X R Y X r Female Female Male Male 1 1 Frequencies Phenotypes Genotypes Frequencies X R X R X r Y X R X r X R Y R r R
    50. 55. Departure from Mendel’s Rules <ul><li>Assumptions drawn from Mendel’s Rules </li></ul><ul><ul><li>All genes are governed by alleles found at a single locus on a pair of homologous chromosomes </li></ul></ul><ul><ul><li>There are two alleles (gene forms) for each characteristic or gene type </li></ul></ul><ul><ul><li>One allele is dominant over the other , which is recessive </li></ul></ul>
    51. 56. Incomplete Dominance <ul><li>Dominance of one allele over another breaks down in incompletely dominant characteristics </li></ul><ul><li>When the heterozygous phenotype is intermediate between the two homozygous phenotypes, the pattern of inheritance is called incomplete dominance </li></ul>
    52. 57. Incomplete Dominance: Homozygous-X Homo Recessive R R (100%) Pink (intermediate) Eggs of Homozygous RR Red Parent Pollen of Homozygous R ' R ' White Parent R' R' R' R R' R R' R R' R Pink Pink Pink Pink 1 Frequencies Phenotypes Genotypes Frequencies R'R R'R R'R R'R
    53. 58. Incomplete Dominance: F 1 X F 1 (25%) (25%) Red White R R' (50%) Pink Eggs of Heterozygous RR ' Pink F 1 Parent Pollen of Heterozygous RR ' Pink F 1 Parent R R' R' R R R' R R R' R' 1 1 Red Pink Pink White Frequencies Phenotypes Genotypes Frequencies RR R'R' RR' R'R 2
    54. 59. Human Eye Color AB Ab aB ab AB Ab aB ab EGGS SPERM Mother AaBb Father AaBb AABB AABb AaBB AaBb black dark brown dark brown light brown AAbB dark brown AAbb light brown AabB light brown Aabb blue aABB aABb aaBB aaBb dark brown light brown light brown blue aABb aABb aaBb aabb light brown blue blue light blue
    55. 60. Multiple Alleles <ul><li>A species may have more than two alleles for a given characteristic </li></ul><ul><ul><li>Each individual still carries two alleles for this characteristic </li></ul></ul>
    56. 61. Multiple Alleles <ul><li>Examples of multiple allelism </li></ul><ul><ul><li>Thousands of alleles for eye color in fruit flies, producing white, yellow, orange, pink, brown, or red eyes </li></ul></ul><ul><ul><li>Human blood group genes producing blood types A, B, AB, and O </li></ul></ul><ul><ul><ul><li>Three alleles in this system: A , B , and O </li></ul></ul></ul>
    57. 62. Codominance <ul><li>Some alleles are always expressed even in combination with other alleles </li></ul><ul><li>Heterozygotes display phenotypes of both the homozygote phenotypes in codominance </li></ul>
    58. 63. Codominance <ul><li>Example: Human blood group alleles </li></ul><ul><ul><li>Alleles A and B are codominant </li></ul></ul><ul><ul><li>Type AB blood is seen where individual has the genotype AB </li></ul></ul>
    59. 64. Human ABO Blood Group 10% 40% 46% 4% B or AB A or AB O,AB, A,B (universal) AB (universal) B or O A or O O AB, A, B, O (universal) A B Both Neither BB or BO AA or AO OO AB O AB B A Freq Donates Re- ceives Anti- bodies RBCs Genotype Type
    60. 65. Polygenic Inheritance <ul><li>Some characteristics show a range of continuous phenotypes instead of discrete, defined phenotypes </li></ul><ul><ul><li>Examples include human height, skin color, and body build, and grain color in wheat </li></ul></ul>
    61. 66. Polygenic Inheritance <ul><li>Phenotypes produced by polygenic inheritance are governed by the interaction of more than two genes at multiple loci </li></ul><ul><li>Human skin color is controlled by at least 3 genes, each with pairs of incompletely dominant alleles </li></ul>
    62. 68. Pleiotropy <ul><li>Some alleles of a characteristic may create multiple phenotypic effects ( pleiotropy ) </li></ul><ul><ul><li>Mendel’s rules specify only one phenotype possible for any allele </li></ul></ul>
    63. 69. Pleiotropy <ul><li>Example: The SRY gene in male humans </li></ul><ul><ul><li>SRY gene stimulates development of gonads into testes, which in turn stimulate development of the prostate, seminal vesicles, penis, and scrotum </li></ul></ul>
    64. 70. Pedigree Analysis <ul><li>Records of gene expression over several generations of a family can be diagrammed </li></ul><ul><li>Careful analysis of this diagram (a pedigree ) can reveal inheritance pattern of a trait </li></ul><ul><li>Pedigree analysis is often combined with molecular genetics technology to elucidate gene action and expression </li></ul>
    65. 71. How to Read Pedigrees = male = female = parents or = individual who shows the trait or = heterozygous carrier of autosomal trait = offspring 1 2 3 I, II, III, IV, or V = generation
    66. 72. A Recessive Pedigree
    67. 73. Pedigrees: Legacy of Queen Victoria
    68. 74. Sickle-Cell Anemia <ul><li>Hemoglobin is an oxygen-transporting protein found in red blood cells </li></ul><ul><li>A mutant hemoglobin gene causes hemoglobin molecules in blood cells to clump together </li></ul><ul><ul><li>Red blood cells take on a sickle (crescent) shape and easily break </li></ul></ul><ul><ul><li>Blood clots can form, leading to oxygen starvation of tissues and paralysis </li></ul></ul><ul><ul><li>Condition is known as sickle-cell anemia </li></ul></ul>
    69. 75. Normal Red Blood Cells
    70. 76. Sickled Cells
    71. 77. Sex-Linked Genetic Disorders <ul><li>Several defective alleles for characteristics encoded on the X chromosome are known </li></ul><ul><li>Sex-linked disorders appear more frequently in males and often skip generations </li></ul><ul><li>Examples of sex-linked (X-linked) disorders </li></ul><ul><ul><li>Red-green color blindness </li></ul></ul>
    72. 80. Non-Disjunction Incorrect separation of chromosomes or chromatids in meiosis known as non-disjunction Most embryos arising from gametes with abnormal chromosome numbers abort spontaneously (are miscarried) Some combinations of abnormal chromosome number survive to birth or beyond
    73. 83. Incidence of Down Syndrome Age of Mother (years) Number per 1000 Births 10 20 30 40 50 0 100 200 300 400
    74. 84. The end

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