Get Ready for A & P!

1. Get Ready for A & P! Genetics, Genetic Abnormalities & Bioethics

2. Early Ideas about Heredity • People knew that sperm and eggs transmitted information about traits • Blending theory - traits blended • Problem: • Would expect variation to disappear • However, variation in traits persists

3. Gregor Mendel • The founder of modern genetics Fig. 11-2, p.170

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

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

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

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

8. A pair of homologous chromosomes, each in the unduplicated state (most often, one from a male parent and its partner from a female parent) A gene locus (plural, loci), the location for a specific gene on a chromosome. Alleles are at corresponding loci on a pair of homologous chromosomes A pair of alleles may be identical or nonidentical. They are represented in the text by letters such as D or d Three pairs of genes (at three loci on this pair of homologous chromosomes); same thing as three pairs of alleles Fig. 11-4, p.171

9. Genotype & Phenotype • Genotype refers to particular genes an individual carries • Phenotype refers to an individual’s observable traits • Cannot always determine genotype by observing phenotype • 3 major genotypes : homozygous dominant (AA) homozygous recessive (aa) heterozygous (Aa)

10. Tracking Generations • Parental generation P mates to produce • First-generation offspring F1 mate to produce • Second-generation offspring F2

11. Monohybrid Crosses Experimental intercross between two F1 heterozygotes AA X aa Aa (F1 monohybrids) Aa X Aa ?

12. Mendel’s Monohybrid Cross Results 5,474 round 1,850 wrinkled 6,022 yellow 2,001 green 882 inflated 299 wrinkled 428 green 152 yellow F2 plants showed dominant-to-recessive ratio that averaged 3:1 705 purple 224 white 651 long stem 207 at tip 787 tall 277 dwarf Fig. 11-6, p. 172

13. Trait Studied Dominant Form Recessive Form F2 Dominant-to- Recessive Ratio SEED SHAPE 5,474 round 1,850 wrinkled 2.96:1 SEED COLOR 6,022 yellow 2,001 green 3.01:1 POD SHAPE 882 inflated 299 wrinkled 2.95:1 POD COLOR 428 green 152 yellow 2.82:1 FLOWER COLOR 705 purple 224 white 3.15:1 FLOWER POSITION 651 long stem 207 at tip 3.14:1 STEM LENGTH 787 tall 277 dwarf 2.84:1 Fig. 11-6, p.172

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

15. True-breeding homozygous recessive parent plant F1PHENOTYPES aa True-breeding homozygous dominant parent plant Aa Aa a a Aa Aa A AA A Aa Aa Aa Aa An F1 plant self-fertilizes and produces gametes: F2PHENOTYPES Aa AA Aa A a A AA Aa a Aa aa Aa aa Monohybrid CrossIllustrated Figure 11.7Page 173

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

17. Punnett Squares of Test Crosses True-breeding homozygous recessive parent plant F1 PHENOTYPES aa True-breeding homozygous dominant parent plant Aa Aa a a Aa Aa A AA Aa Aa A Aa Aa Fig. 11-7b1, p.173

18. Punnett Squares of Test Crosses An F1 plant self-fertilizes and produces gametes: F2 PHENOTYPES Aa AA Aa A a AA Aa A Aa aa a Aa aa Fig. 11-7b2, p.173

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

20. Dihybrid Cross: F1 Results purple flowers, tall white flowers, dwarf TRUE- BREEDING PARENTS: AABB x aabb GAMETES: AB AB ab ab AaBb F1 HYBRID OFFSPRING: All purple-flowered, tall

21. Dihybrid Cross: F2 Results X AaBb AaBb 1/4 AB 1/4 Ab 1/4 aB 1/4 ab 9/16 purple-flowered, tall 1/4 AB 1/16 AABB 1/16 AABb 1/16 AaBB 1/16 AaBb 3/16 purple-flowered, dwarf 3/16 white-flowered, tall 1/16 AaBb 1/16 AAbb 1/16 Aabb 1/4 Ab 1/16 AABb 1/16 white-flowered, dwarf 1/16 AaBB 1/16 aaBB 1/16 aaBb 1/4 aB 1/16 AaBb 1/16 Aabb 1/16 aaBb 1/16 aabb 1/16 AaBb 1/4 ab

22. Dominance Relations Complete dominance Incomplete dominance Codominance

23. Incomplete Dominance Incomplete Dominance X Homozygous parent Homozygous parent All F1 are heterozygous X F2 shows three phenotypes in 1:2:1 ratio

24. Incomplete Dominance homozygous parent X homozygous parent All F1 offspring heterozygous for flower color: Cross two of the F1 plants and the F2 offspring will show three phenotypes in a 1:2:1 ratio: Fig. 11-11, p.176

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

26. ABO Blood Type Range of genotypes: IAIA IBIB or or IAi IAIB IBi ii Blood Types: A AB B O Fig. 11-10a, p.176

27. ABO and Transfusions • 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

28. Temperature Effects on Phenotype • 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 Figure 11.16Page 179

29. Autosomal Recessive Inheritance Patterns If parents are both heterozygous, child will have a 25% chance of being affected Fig. 12-10b, p. 191

30. Fig. 11-21, p.183

31. Autosomal Dominant Inheritance Trait typically appears in every generation Fig. 12-10a, p. 190

32. Huntington Disorder Autosomal dominant allele Causes involuntary movements, nervous system deterioration, death Symptoms don’t usually show up until person is past age 30 People often pass allele on before they know they have it

33. Achondroplasia Autosomal dominant allele In homozygous form usually leads to stillbirth Heterozygotes display a type of dwarfism Have short arms and legs relative to other body parts

34. Autosomal Dominant Inheritance Fig. 12-5, p.190

35. Sex Chromosomes Discovered in late 1800s Mammals, fruit flies XX is female, XY is male In other groups XX is male, XY female Human X and Y chromosomes function as homologues during meiosis

36. The X Chromosome Carries more than 2,300 genes Most genes deal with nonsexual traits Genes on X chromosome can be expressed in both males and females

37. The Y Chromosome Fewer than two dozen genes identified One is the master gene for male sex determination SRY gene (sex-determining region of Y) SRY present, testes form SRY absent, ovaries form

38. Crossing Over • Each chromosome becomes zippered to its homologue • All four chromatids are closely aligned • Nonsister chromosomes exchange segments

39. Effect of Crossing Over After crossing over, each chromosome contains both maternal and paternal segments Creates new allele combinations in offspring

40. Crossover Frequency Proportional to the distance that separates genes A B C D Crossing over will disrupt linkage between A and B more often than C and D In-text figurePage 178

41. X-Linked Recessive Inheritance Males show disorder more than females Son cannot inherit disorder from his father Fig. 12-10, p.194

42. Examples of X-Linked Traits Color blindness Inability to distinguish among some of all colors Hemophilia Blood-clotting disorder 1/7,000 males has allele for hemophilia A Was common in European royal families

43. Color Blindness Fig. 12-12, p.195

44. Pedigree Symbols male female marriage/mating offspring in order of birth, from left to right Individual showing trait being studied sex not specified generation I, II, III, IV... Fig. 12-19a, p.200

45. Duplication Gene sequence that is repeated several to hundreds of times Duplications occur in normal chromosomes May have adaptive advantage Useful mutations may occur in copy

46. Duplication normal chromosome one segment repeated three repeats

47. Deletion Loss of some segment of a chromosome Most are lethal or cause serious disorder

48. Deletion Cri-du-chat Fig. 12-13, p.196

49. Inversion A linear stretch of DNA is reversed within the chromosome segments G, H, I become inverted In-text figurePage 196

50. Translocation A piece of one chromosome becomes attached to another nonhomologous chromosome Most are reciprocal Philadelphia chromosome arose from a reciprocal translocation between chromosomes 9 and 22