1. Observable Patterns of Inheritance Chapter 11

2. Earlobe Variation Whether a person has attached or detached earlobes depends on a single gene Whether a person has attached or detached earlobes depends on a single gene Attached earlobes: two copies of the recessive allele for this gene Attached earlobes: two copies of the recessive allele for this gene Detached earlobes: either one or two copies of the dominant allele Detached earlobes: either one or two copies of the dominant allele

3. Early Ideas about Heredity People knew that sperm and eggs transmitted information about traits People knew that sperm and eggs transmitted information about traits Blending theory Blending theory Problem: Problem: Would expect variation to disappear Would expect variation to disappear What would you expect to happen with trait such as height? What would you expect to happen with trait such as height? Variation in traits persists Variation in traits persists

4. Gregor Mendel Gregor Mendel Strong background in plant breeding and mathematics Strong background in plant breeding and mathematics Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring

5. Genes Genes Units of information about specific traits Units of information about specific traits Passed from parents to offspring Passed from parents to offspring Each has a specific location (locus) on a chromosome Each has a specific location (locus) on a chromosome

6. Alleles Different molecular forms of a gene Different molecular forms of a gene Arise by mutation Arise by mutation Dominant allele masks a recessive allele that is paired with it Dominant allele masks a recessive allele that is paired with it

7. Allele Combinations Homozygous Homozygous having two identical alleles at a locus having two identical alleles at a locus AA or aa AA or aa Heterozygous Heterozygous having two different alleles at a locus having two different alleles at a locus Aa Aa

8. Genetic Terms A pair of homologous chromosomes A gene locus A pair of alleles Three pairs of genes Figure 11.4 Page 179

9. Genotype & Phenotype Genotype refers to particular genes an individual carries Genotype refers to particular genes an individual carries Phenotype refers to an individual’s observable traits Phenotype refers to an individual’s observable traits Cannot always determine genotype by observing phenotype Cannot always determine genotype by observing phenotype

10. Tracking Generations Parental generation P Parental generation P mates to produce First-generation offspring F 1 First-generation offspring F 1 mate to produce Second-generation offspring F 2 Second-generation offspring F 2

11. Monohybrid Crosses Experimental intercross between two F 1 heterozygotes AA X aaAa (F 1 monohybrids) Aa X Aa ?

12. Mendel’s Monohybrid Cross Results 787 tall277 dwarf 651 long stem207 at tip 705 purple224 white 152 yellow428 green 299 wrinkled882 inflated 6,022 yellow2,001 green 5,474 round1,850 wrinkled F 2 plants showed dominant-to- recessive ratio that averaged 3:1 Figure 11.5 Page 180

13. Probability The chance that each outcome of a given event will occur is proportional to the number of ways that event can be reached

14. Monohybrid Cross Illustrated True-breeding homozygous recessive parent plant True-breeding homozygous dominant parent plant An F 1 plant self-fertilizes and produces gametes: F 1 PHENOTYPES F 2 PHENOTYPES aa Aa AA aaAa AA aa A A A A aa a a AA Figure 11.7 Page 181

15. Mendel’s Theory of Segregation Mendel’s Theory of Segregation An individual inherits a unit of information (allele) about a trait from each parent An individual inherits a unit of information (allele) about a trait from each parent During gamete formation, the alleles segregate from each other During gamete formation, the alleles segregate from each other

16. Test Cross Individual that shows dominant phenotype is crossed with individual with recessive phenotype Individual that shows dominant phenotype is crossed with individual with recessive phenotype Examining offspring allows you to determine the genotype of the dominant individual Examining offspring allows you to determine the genotype of the dominant individual

17. Punnett Squares of Test Crosses Homozygous recessive a A aaa Aa aa Homozygous recessive a A AAa Two phenotypesAll dominant phenotype

18. Dihybrid Cross Experimental cross between individuals that are homozygous for different versions of two traits

19. Dihybrid Cross: F 1 Results AABBaabbx AaBb AB ab TRUE- BREEDING PARENTS: GAMETES : F 1 HYBRID OFFSPRING: purple flowers, tall white flowers, dwarf All purple-flowered, tall Figure 11.9 (1) Page 183

20. 1/16 aaBB 1/16 aaBb 1/16 aaBb 1/16 Aabb 1/16 Aabb 1/16 AAbb 1/16 AABB 1/16 AABb 1/16 AaBB 1/16 AaBb 1/16 AABb 1/16 AaBb 1/16 AaBB 1/16 AaBb 1/16 AaBb 1/4 AB1/4 Ab1/4 aB1/4 ab 1/16 aabb 1/4 AB 1/4 Ab 1/4 aB 1/4 ab AaBb X 1/16 white-flowered, dwarf 3/16 white-flowered, tall 3/16 purple-flowered, dwarf 9/16 purple-flowered, tall Dihybrid Cross: F 2 Results Figure 11.9(2) Page 183

21. Independent Assortment Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis

22. Independent Assortment Metaphase I: Metaphase II: Gametes: 1/4 AB1/4 ab1/4 Ab1/4 aB AAAA AAAA AAAA BB BB BB BB BBBB aaaa aaaa aaaa bbbb bbbb bbbb OR

23. Impact of Mendel’s Work Mendel presented his results in 1865 Mendel presented his results in 1865 Paper received little notice Paper received little notice Mendel discontinued his experiments in 1871 Mendel discontinued his experiments in 1871 Paper rediscovered in 1900 Paper rediscovered in 1900

24. Dominance Relations Complete dominance Incomplete dominance Codominance

25. Incomplete Dominance Incomplete Dominance X Homozygous parent Homozygous parent All F 1 are heterozygous X F 2 shows three phenotypes in 1:2:1 ratio Incomplete Dominance Figure 11.10 Page 184

26. Codominance: ABO Blood Types Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells Two alleles (I A and I B ) are codominant when paired Two alleles (I A and I B ) are codominant when paired Third allele (i) is recessive to others Third allele (i) is recessive to others

27. ABO Blood Type: Allele Combinations Range of genotypes: Blood types: I A I A iI A I B I B i I B ii AABBO or Figure 11.11 Page 184

28. ABO and Transfusions Recipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surface Recipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surface Type O is universal donor because it has neither type A nor type B glycolipid Type O is universal donor because it has neither type A nor type B glycolipid

29. Pleiotropy Alleles at a single locus may have effects on two or more traits Alleles at a single locus may have effects on two or more traits Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin

30. Epistasis Interaction between the products of gene pairs Interaction between the products of gene pairs Common among genes for hair color in mammals Common among genes for hair color in mammals

31. Coat Color in Retrievers bbeeBBEEX F 1 puppies are all BbEe BBEE BBEe BbEE BbEe Bbee BbEe Bbee BBEeBbEEBbEe BBeeBbEe bbeebbEe bbEEbbEe BEBebEbe BE Be bE be black brown yellow F 2 puppies Figure 11.13 Page 186

32. Comb Shape in Poultry 9/16 walnut3/16 rose3/16 pea 1/16 single rrpp RRpp (rose comb) rrPP (pea comb) RrPp (all walnut comb) P: F2:F2: F1:F1: X RRPP RRPp RrPP RrPp RRpp Rrpp rrPP rrPp Figure 11.15 Page 187

33. Campodactyly: Unexpected Phenotypes Effect of allele varies: Effect of allele varies: Bent fingers on both hands Bent fingers on both hands Bent fingers on one hand Bent fingers on one hand No effect No effect Many factors affect gene expression Many factors affect gene expression

34. Continuous Variation Continuous Variation A more or less continuous range of small differences in a given trait among individuals A more or less continuous range of small differences in a given trait among individuals The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait

35. Human Variation Some human traits occur as a few discrete types Some human traits occur as a few discrete types Attached or detached earlobes Attached or detached earlobes Many genetic disorders Many genetic disorders Other traits show continuous variation Other traits show continuous variation Height Height Weight Weight Eye color Eye color

36. Describing Continuous Variation Range of values for the trait Number of individuals with some value of the trait (line of bell-shaped curve indicates continuous variation in population) Range of values for the trait Number of individuals with some value of the trait

37. Temperature Effects on Phenotype Rabbit is homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin- producing pathway Rabbit is homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin- producing pathway Melanin is produced in cooler areas of body Melanin is produced in cooler areas of body Figure 11.18 Page 190

38. Environmental Effects on Plant Phenotype Environmental Effects on Plant Phenotype Hydrangea macrophylla Hydrangea macrophylla Action of gene responsible for floral color is influenced by soil acidity Action of gene responsible for floral color is influenced by soil acidity Flower color ranges from pink to blue Flower color ranges from pink to blue