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Mendelian Genetics Figure 11.1
Figure 11.1 What principles of inheritance did Gregor Mendel discover by breeding garden pea plants? 1
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P Generation F1 Generation F2 Generation Appearance: Genetic makeup:
Figure P Generation Appearance: Genetic makeup: Purple flowers PP White flowers pp Gametes: P p F1 Generation Appearance: Genetic makeup: Purple flowers Pp Gametes: P p Sperm from F1 (Pp) plant Figure Mendel’s law of segregation (step 3) F2 Generation P p P Eggs from F1 (Pp) plant PP Pp p Pp pp 3 : 1 2
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PP (homozygous) Pp (heterozygous) Pp (heterozygous) pp (homozygous)
Figure 11.6 Phenotype Genotype PP (homozygous) Purple 1 3 Pp (heterozygous) Purple 2 Pp (heterozygous) Purple Figure 11.6 Phenotype versus genotype pp (homozygous) 1 White 1 Ratio 3:1 Ratio 1:2:1 3
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Table 11.1 Table 11.1 The results of Mendel’s F1 crosses for seven characters in pea plants 4
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independent assortment
Figure 11.8 Experiment P Generation YYRR yyrr Gametes YR yr F1 Generation YyRr Predictions Hypothesis of dependent assortment Hypothesis of independent assortment Sperm or Predicted offspring in F2 generation YR Yr yR yr Sperm YR yr YR YYRR YYRr YyRR YyRr YR YYRR YyRr Yr Eggs YYRr YYrr YyRr Yyrr Eggs Figure 11.8 Inquiry: Do the alleles for one character segregate into gametes dependently or independently of the alleles for a different character? yr YyRr yyrr yR YyRR YyRr yyRR yyRr yr Phenotypic ratio 3:1 YyRr Yyrr yyRr yyrr 9 16 3 16 3 16 1 16 Phenotypic ratio 9:3:3:1 Results 315 108 101 32 Phenotypic ratio approximately 9:3:3:1 5
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Allele for purple flowers
Figure 11.4 Allele for purple flowers Pair of homologous chromosomes Locus for flower-color gene Figure 11.4 Alleles, alternative versions of a gene Allele for white flowers 6
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Segregation of alleles into eggs Segregation of alleles into sperm
Figure 11.9 Rr Rr Segregation of alleles into eggs Segregation of alleles into sperm Sperm R r R R r R R Figure 11.9 Segregation of alleles and fertilization as chance events Eggs r r R r r 7
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Multiplication Rule: The probability that two or more events will occur together is the product of the individual probabilities Addition Rule: the probability that any one of two mutually exclusive events will occur is calculated by adding together their individual probabilities.
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P Generation Red CRCR White CWCW Gametes Pink CRCW F1 Generation
Figure P Generation Red CRCR White CWCW Gametes CR CW Pink CRCW F1 Generation Gametes CR CW Figure Incomplete dominance in snapdragon color (step 3) Sperm CR CW F2 Generation CR CRCR CRCW Eggs CW CRCW CWCW 9
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(a) The three alleles for the ABO blood groups and their carbohydrates
Figure 11.11 (a) The three alleles for the ABO blood groups and their carbohydrates Allele IA IB i Carbohydrate A B none (b) Blood group genotypes and phenotypes Genotype IAIA or IAi IBIB or IBi IAIB ii Figure Multiple alleles for the ABO blood groups Red blood cell appearance Phenotype (blood group) A B AB O 10
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(parents, aunts, and uncles) FF or Ff ff ff Ff Ff ff
Figure 11.14b Key Male Affected male Mating Offspring, in birth order (first-born on left) Female Affected female 1st generation (grandparents) Ff Ff ff Ff 2nd generation (parents, aunts, and uncles) FF or Ff ff ff Ff Ff ff 3rd generation (two sisters) Figure 11.14b Pedigree analysis (part 2: attached earlobe) ff FF or Ff Attached earlobe Free earlobe (b) Is an attached earlobe a dominant or recessive trait? 11
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Dwarf Dd Normal dd Dd Dwarf dd Normal Dd Dwarf dd Normal
Figure 11.16 Parents Dwarf Dd Normal dd Sperm D d Eggs Dd Dwarf dd Normal d Figure Achondroplasia: a dominant trait Dd Dwarf dd Normal d 12
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The Chromosomal Basis of Inheritance
12 The Chromosomal Basis of Inheritance
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Figure 12.1 Figure 12.1 Where are Mendel's hereditary factors located in the cell? 14
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/ / / / Figure 12.2 Figure 12.2 The chromosomal basis of Mendel’s laws
P Generation Yellow-round seeds (YYRR) Green-wrinkled seeds (yyrr) Y y r R Y R r y Meiosis Fertilization R Y y r Gametes All F1 plants produce yellow-round seeds (YyRr). F1 Generation R R y y r r Y Y Meiosis LAW OF SEGREGATION The two alleles for each gene separate. LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently. R r Metaphase I r R Y y Y y 1 1 R r r R Anaphase I Y y Y y Figure 12.2 The chromosomal basis of Mendel’s laws R r Metaphase II r R 2 2 Y y Y y y Y Y y Y Y y y R R r r r r R R 1 4 / YR 1 4 / yr YR 1 4 / Yr 1 4 / yR F2 Generation An F1 F1 cross-fertilization 3 Fertilization recombines the R and r alleles at random. 3 Fertilization results in the 9:3:3:1 phenotypic ratio in the F2 generation. 9 : 3 : 3 : 1 15
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P Generation Yellow-round Green-wrinkled seeds (YYRR) seeds (yyrr)
Figure 12.2a P Generation Yellow-round seeds (YYRR) Green-wrinkled seeds (yyrr) Y y r R R r Y y Meiosis Figure 12.2a The chromosomal basis of Mendel’s laws (part 1) Fertilization R Y y r Gametes 16
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All F1 plants produce yellow-round seeds (YyRr). F1 Generation
Figure 12.2b All F1 plants produce yellow-round seeds (YyRr). F1 Generation R R y y r r Y Y Meiosis LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently. LAW OF SEGREGATION The two alleles for each gene separate. R r r R Metaphase I Y y Y y 1 1 R r r R Anaphase I Y y Y y Metaphase II R r r R Figure 12.2b The chromosomal basis of Mendel’s laws (part 2) 2 2 Y y Y y y Y Y Y Y y y y R R r r r r R R 1 4 YR 1 4 yr 1 4 Yr 1 4 yR 17
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An F1 F1 cross-fertilization 3 Fertilization results in the 9:3:3:1
Figure 12.2c LAW OF SEGREGATION LAW OF INDEPENDENT ASSORTMENT F2 Generation 3 Fertilization recombines the R and r alleles at random. An F1 F1 cross-fertilization 3 Fertilization results in the 9:3:3:1 phenotypic ratio in the F2 generation. 9 : 3 : 3 : 1 Figure 12.2c The chromosomal basis of Mendel’s laws (part 3) 18
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Experiment Conclusion P Generation P Generation F1 Generation
Figure 12.4 Experiment Conclusion P Generation P Generation w w X X X Y w F1 Generation All offspring had red eyes. w Sperm Eggs F1 Generation w w w Results w F2 Generation w Sperm Eggs w w Figure 12.4 Inquiry: In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have? w F2 Generation w w w w w 19
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P Generation F1 Generation F2 Generation
Figure 12.4a Experiment P Generation F1 Generation All offspring had red eyes. Results Figure 12.4a Inquiry: In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have? (part 1: experiment and results) F2 Generation 20
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P Generation F1 Generation F2 Generation
Figure 12.4b Conclusion P Generation w w X X X Y w w Sperm Eggs F1 Generation w w w w w Sperm Figure 12.4b Inquiry: In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have? (part 2: conclusion) Eggs w w w F2 Generation w w w w w 21
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Figure 12.5 X Y Figure 12.5 Human sex chromosomes 22
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44 XY 44 XX Parents 22 X 22 X 22 Y or Sperm Egg 44 XX 44
Figure 12.6 44 XY 44 XX Parents 22 X 22 X 22 Y or Sperm Egg Figure 12.6 The mammalian X-Y chromosomal system of sex determination 44 XX 44 XY or Zygotes (offspring) 23
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Sperm Eggs (a) Sperm Sperm Eggs Eggs (b) (c) XNXN XnY Xn Y XN XNXn XNY
Figure 12.7 XNXN XnY Xn Y Sperm Eggs XN XNXn XNY XN XNXn XNY (a) XNXn XNY XNXn XnY Figure 12.7 The transmission of X-linked recessive traits XN Y Sperm Xn Y Sperm Eggs XN XNXN XNY Eggs XN XNXn XNY Xn XNXn XnY Xn XnXn XnY (b) (c) 24
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X chromosomes Allele for orange fur Early embryo: Allele for black fur
Figure 12.8 X chromosomes Allele for orange fur Early embryo: Allele for black fur Cell division and X chromosome inactivation Two cell populations in adult cat: Active X Inactive X Active X Black fur Orange fur Figure 12.8 X inactivation and the tortoiseshell cat 25
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Figure 12.8a Figure 12.8a X inactivation and the tortoiseshell cat (photo) 26
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b vg b vg F1 dihybrid female and homozygous recessive male
Figure 12.UN01 b vg b vg F1 dihybrid female and homozygous recessive male in testcross b vg b vg b vg b vg Figure 12.UN01 In-text figure, testcross, p. 234 Most offspring or b vg b vg 27
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Figure 12.9 Experiment P Generation (homozygous) Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b b vg vg b b vg vg F1 dihybrid testcross Homozygous recessive (black body, vestigial wings) Wild-type F1 dihybrid (gray body, normal wings) b b vg vg b b vg vg Testcross offspring Eggs b vg b vg b vg b vg Wild-type (gray-normal) Black- vestigial Gray- vestigial Black- normal b vg Figure 12.9 Inquiry: How does linkage between two genes affect inheritance of characters? Sperm b b vg vg b b vg vg b b vg vg b b vg vg PREDICTED RATIOS Genes on different chromosomes: 1 : 1 : 1 : 1 Genes on some chromosome: 1 : 1 : : Results 965 : 944 : 206 : 185 28
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(gray body, normal wings)
Figure 12.9a Experiment P Generation (homozygous) Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b b vg vg b b vg vg F1 dihybrid testcross Homozygous recessive (black body, vestigial wings) Wild-type F1 dihybrid (gray body, normal wings) Figure 12.9a Inquiry: How does linkage between two genes affect inheritance of characters? (part 1: experiment) b b vg vg b b vg vg 29
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Wild-type (gray-normal) Black- vestigial Gray- vestigial Black- normal
Figure 12.9b Experiment Testcross offspring Eggs b vg b vg b vg b vg Wild-type (gray-normal) Black- vestigial Gray- vestigial Black- normal b vg Sperm b b vg vg b b vg vg b b vg vg b b vg vg PREDICTED RATIOS Figure 12.9b Inquiry: How does linkage between two genes affect inheritance of characters? (part 2: results) Genes on different chromosomes: 1 : 1 : 1 : 1 Genes on same chromosome: 1 : 1 : : Results 965 : 944 : 206 : 185 30
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Gametes from yellow-round dihybrid parent (YyRr)
Figure 12.UN02 Gametes from yellow-round dihybrid parent (YyRr) YR yr Yr yR Gametes from green- wrinkled homozygous recessive parent (yyrr) yr YyRr yyrr Yyrr yyRr Figure 12.UN02 In-text figure, Punnett square, p. 236 Parental- type offspring Recombinant offspring 31
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Recombination of Linked Genes: Crossing Over
Morgan discovered that even when two genes were on the same chromosome, some recombinant phenotypes were observed He proposed that some process must occasionally break the physical connection between genes on the same chromosome That mechanism was the crossing over between homologous chromosomes Animation: Crossing Over 32
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Figure 12.10 Chromosomal basis for recombination of linked genes
P generation (homozygous) Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b vg+ b vg b vg+ b vg F1 dihybrid testcross Wild-type F1 dihybrid (gray body, normal wings) Homozygous recessive (black body, vestigial wings) b vg+ b vg b vg b vg Replication of chromosomes Replication of chromosomes b vg+ b vg b vg+ b vg b vg b vg b vg b vg Meiosis I b vg+ Meiosis I and II b vg b vg b vg Recombinant chromosomes Meiosis II Figure Chromosomal basis for recombination of linked genes b vg+ b vg b vg b vg Eggs Testcross offspring 965 Wild type (gray-normal) 944 Black- vestigial 206 Gray- vestigial 185 Black- normal b vg b vg b vg b vg b vg b vg b vg b vg b vg Sperm Parental-type offspring Recombinant offspring Recombination frequency 391 recombinants 17% 2,300 total offspring 33
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P generation (homozygous)
Figure 12.10a P generation (homozygous) Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b vg+ b vg b vg+ b vg Wild-type F1 dihybrid (gray body, normal wings) Figure 12.10a Chromosomal basis for recombination of linked genes (part 1: F1 dihybrid) b vg+ b vg 34
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F1 dihybrid testcross b vg+ b vg Wild-type F1 dihybrid (gray body,
Figure 12.10b F1 dihybrid testcross b vg+ b vg Wild-type F1 dihybrid (gray body, normal wings) Homozygous recessive (black body, vestigial wings) b vg b vg b vg+ b vg b vg+ b vg b vg b vg b vg b vg Meiosis I b vg+ Meiosis I and II b vg b vg Figure 12.10b Chromosomal basis for recombination of linked genes (part 2: testcross) b vg Recombinant chromosomes Meiosis II b+ vg+ b vg b+ vg b vg+ b vg Eggs Sperm 35
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Parental-type offspring Recombinant offspring
Figure 12.10c Recombinant chromosomes b vg+ b vg b vg b vg Eggs Testcross offspring 965 Wild type (gray-normal) 944 Black- vestigial 206 Gray- vestigial 185 Black- normal b vg b vg b vg b vg b vg b vg b vg b vg b vg Figure 12.10c Chromosomal basis for recombination of linked genes (part 3: testcross offspring) Sperm Parental-type offspring Recombinant offspring Recombination frequency 391 recombinants 17% 2,300 total offspring 36
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Results Recombination frequencies 9% 9.5% Chromosome 17% b cn vg
Figure 12.11 Results Recombination frequencies 9% 9.5% Chromosome 17% Figure Research method: constructing a linkage map b cn vg 37
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Mutant phenotypes Short aristae Black body Cinnabar eyes Vestigial
Figure 12.12 Mutant phenotypes Short aristae Black body Cinnabar eyes Vestigial wings Brown eyes 48.5 57.5 67.0 104.5 Figure A partial genetic (linkage) map of a Drosophila chromosome Long aristae (appendages on head) Gray body Red eyes Normal wings Red eyes Wild-type phenotypes 38
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Meiosis I Nondisjunction Figure 12.13-1
Figure Meiotic nondisjunction (step 1) 39
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Meiosis I Nondisjunction Meiosis II Non- disjunction Figure 12.13-2
Figure Meiotic nondisjunction (step 2) 40
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Nondisjunction of homo- logous chromosomes in meiosis I (b)
Figure Meiosis I Nondisjunction Meiosis II Non- disjunction Gametes Figure Meiotic nondisjunction (step 3) n 1 n 1 n − 1 n − 1 n 1 n − 1 n n Number of chromosomes (a) Nondisjunction of homo- logous chromosomes in meiosis I (b) Nondisjunction of sister chromatids in meiosis II 41
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An inversion reverses a segment within a chromosome.
Figure 12.14 (a) Deletion (c) Inversion A deletion removes a chromosomal segment. An inversion reverses a segment within a chromosome. (b) Duplication (d) Translocation A duplication repeats a segment. Figure Alterations of chromosome structure A translocation moves a segment from one chromosome to a nonhomologous chromosome. 42
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(a) Deletion A deletion removes a chromosomal segment. (b) Duplication
Figure 12.14a (a) Deletion A deletion removes a chromosomal segment. (b) Duplication Figure 12.14a Alterations of chromosome structure (part 1: deletion and duplication) A duplication repeats a segment. 43
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An inversion reverses a segment within a chromosome.
Figure 12.14b (c) Inversion An inversion reverses a segment within a chromosome. (d) Translocation Figure 12.14b Alterations of chromosome structure (part 2: inversion and translocation) A translocation moves a segment from one chromosome to a nonhomologous chromosome. 44
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Figure 12.15 Figure Down syndrome 45
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Figure 12.15a Figure 12.15a Down syndrome (part 1: karotype) 46
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Figure 12.15b Figure 12.15b Down syndrome (part 2: photo) 47
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Translocated chromosome 22 (Philadelphia chromosome)
Figure 12.16 Normal chromosome 9 Normal chromosome 22 Reciprocal translocation Figure Translocation associated with chronic myelogenous leukemia (CML) Translocated chromosome 9 Translocated chromosome 22 (Philadelphia chromosome) 48
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Figure 12.UN03a Figure 12.UN03a Skills exercise: using the chi-square test (part 1) 49
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Figure 12.UN03b Figure 12.UN03b Skills exercise: using the chi-square test (part 2) 50
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This F1 cell has 2n 6 chromo- somes and is heterozygous
Figure 12.UN04 Sperm Egg C c B b D A d a P generation gametes E e F f This F1 cell has 2n 6 chromo- somes and is heterozygous for all six genes shown (AaBbCcDdEeFf). The alleles of unlinked genes are either on separate chromosomes (such as d and e) or so far apart on the same chromosome (c and f) that they assort independently. Red maternal; blue paternal. D e C B d Figure 12.UN04 Summary of key concepts: linkage A Genes on the same chromosome whose alleles are so close to- gether that they do not assort independently (such as a, b, and c) are said to be genetically linked. E F Each chromosome has hundreds or thousands of genes. Four (A, B, C, F) are shown on this one. a c b 51
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Figure 12.UN05 Figure 12.UN05 Test your understanding, question 10 (tiger swallowtail gynandromorph) 52
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