Principles of Heredity

1. Principles of Heredity What patterns of inheritance can be observed when traits are passed to the next generation?

2. Use of the Garden Pea for Genetics Experiments

3. Use of the Garden Pea for Genetics Experiments

4. Use of the Garden Pea for Genetics Experiments

5. Round seed x Wrinkled seed F1: All round seed coats Principles of Heredity Mendel’s Experiment with Peas F1 round plants x F1 round plants F2: 5474 round: 1850 wrinkled (3/4 round to 1/4 wrinkled)

6. Principles of Heredity • Mendel needed to explain • Why one trait seemed to disappear in the first generation. • 2. Why the same trait reappeared in the second generation in one-fourth of the offspring.

7. Principles of Heredity • Mendel proposed: • Each trait is governed by two factors – now called genes. • 2. Genes are found in alternative forms called alleles. • 3. Some alleles are dominant and mask alleles that are recessive.

8. Mendel’s Experiment with Peas Round seed x Wrinkled seed RR rr F1: All round seed coats Rr Homozygous Dominant Homozygous Recessive Heterozygous Principles of Heredity

9. R R R R Homozygous parents can only pass one form of an allele to their offspring.

10. Heterozygous parents can pass either of two forms of an allele to their offspring. R r R r

11. Principles of Heredity Additional Genetic Terms Genotype: alleles carried by an individual eg. RR, Rr, rr Phenotype: physical characteristic or appearance of an individual eg. Round, wrinkled

12. Mendel’s Principle of Genetic Segregation In the formation of gametes, the members of a pair of alleles separate (or segregate) cleanly from each other so that only one member is included in each gamete. Each gamete has an equal probability of containing either member of the allele pair.

13. Genetic Segregation Parentals: RR x rr F1 x F1: Rr x Rr R R r r R r R r r r R r RR Rr R R Rr Rr R r Rr rr Rr Rr

14. Genotypes and Phenotypes for Petal Color Cross

15. Seven Traits used by Mendel in Genetic Studies

16. Mendel’s Experiment with Peas Round Yellow x Wrinkled Green F1: All round yellow seed coats F1 plants x F1 plants F2: 315 round, yellow 9/16 108 round, green 3/16 101 wrinkled, yellow 3/16 32 wrinkled, green 1/16 Principles of Heredity

17. Principles of Heredity • Mendel needed to explain • Why non-parental combinations appeared in the F2 offspring. • 2. Why the ratio of phenotypes in the F2 generation was 9:3:3:1.

18. Mendel’s Principle of Independent Assortment When gametes are formed, the alleles of one gene segregate independently of the alleles of another gene producing equal proportions of all possible gamete types.

19. Parentals: RRYY x rryy RY RY RY RY ry ry ry ry ry RY Genetic Segregation + Independent Assortment RrYy

20. F1 x F1:RrYy x RrYy RY Ry rY ry RY Ry rY ry RY Ry rY ry RRYY RRYy RrYY RrYy RY Ry rY ry RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy

21. F2 Genotypes and Phenotypes

22. Meiotic Segregation explains Independent Assortment

23. Solving Genetics Problems • Convert parental phenotypes to genotypes • Use Punnett Square to determine genotypes of offspring • Convert offspring genotypes to phenotypes

24. Additional Genetic Patterns

25. ML M X ML M 2/3 tailless + 1/3 tails Lethal Alleles Example: Manx cat ML = tailless, lethal in homozygote M = tail Tailless male x Tailless female MLM x MLM MLML MLM dies tailless MM MLM tailless tail

26. Multiple Alleles • Multiple Alleles: three or more alleles exist for one trait (Note: A diploid individual can only carry two alleles at once.)

27. Codominance • Codominance: Neither allele masks the other so that effects of both alleles are observed in heterozygote without blending IA =IB > i IA and IB are codominant. IA and IB are completely dominant over i.

28. Codominance

29. IAi IBi Antigens on Red Blood Cells IAIB

30. Inheritance of Rh Factor *Although there are multiple R alleles, R1, R2, R3, etc. all are completely dominant over all of the r alleles, r1, r2, r3, etc.

31. IBr ir Multiple Alleles and Codominance Type A, Rh positive x Type B, Rh negative (father is Type O, Rh negative) (mother is Type O, Rh negative) IA iRr x IB irr IAR IAr iR ir IAIBrr IBiRr IBirr IAIBRr IAirr iiRr iirr IAiRr Phenotypic Ratio of Offspring 1/8 Type AB positive 1/8 Type A positive 1/8 Type AB negative 1/8 Type A negative 1/8 Type B positive 1/8 Type O positive 1/8 Type B negative 1/8 Type O negative

32. RR x R’R’ Red White RR’ pink Incomplete Dominance Incomplete dominance: neither allele masks the other and both are observed as a blending in the heterozygote Four o’clock flowers R = red, R’ = white

33. ½ R ½ R’ ½ R ½ R’ Incomplete Dominance RR’ x RR’ Pink x Pink ¼ RR ¼ RR’ ¼ RR’ ¼ R’R’ Genotypic Ratio: ¼ RR + ½ RR’ +1/4 R’R’ Phenotypic Ratio: ¼ red + ½ pink + ¼ white

34. Epistasis • An allele of one gene masks the expression of alleles of another gene and expresses its own phenotype instead.

35. Epistasis H = enzyme that attaches antigen H to protein on red blood cells h= no enzyme to attach antigen H Antigens A and B of ABO blood typing (from alleles IA and IB) are attached to antigen H. Someone with the genotype hh will have Type O blood irrespective of their genotype for the I alleles.

36. IBH IBh ih iH IAH IAh iH ih Epistasis IAiHh x IBiHh IAIBHH IAiHH IAIBHh IAiHh Type A = 3/16 Type B = 3/16 Type AB = 3/16 *Type O = 7/16 IAIBhh* IAihh* IAIBHh IAiHh iiHh* IBiHH IBiHh iiHH* IBihh* iiHh* IBiHh iihh*

37. Pleiotropic Effects One gene affects many phenotypic characteristics

38. Linked Genes

39. How Do We Study Gene Linkage? Example from the Fruit Fly Red eyes, x Pink eyes Beige body Ebony body RRBB rrbb F1: Red eyes, Beige body RrBb

40. How Do We Study Gene Linkage? How Do We Study Gene Linkage? Testcross: cross to individual of known genotype F1:Red eyes X Pink eyes Beige body Ebony body RrBb rrbb

41. How Do We Study Gene Linkage?

42. How Do We Study Gene Linkage? If genes are linked: Red eyes, x Pink eyes Beige body Ebony body R B r b R B r b F1: Red eyes, Beige body R B r b

43. R B r b R B R b r b r B How Do We Study Gene Linkage? F1: Red eyes, Beige body X Four types of gametes are produced Parental Recombinant

44. How Do We Study Gene Linkage? F1:Red eyes X Pink eyes Beige body Ebony body R B r b r b r b r B R B r b R b r b r b r b r b r b

45. How Do We Study Gene Linkage?

46. Genetic Map Units 1% recombination = 1 map unit 108 + 112 x 100 = 22% 1000 These genes are located 22 map units apart on the same chromosome. Map is drawn as: R B I 22 map units I

47. R B r b X 39% 11% R B R b 39% 11% r b r B 78% 22% How Do We Study Gene Linkage? Knowing the gene distance allows us to predict the expected percentages of each type of gamete. Parental Recombinant

48. Limits of Genetic Mapping Genes that are 50 map units apart will appear to assort independently.

49. Gene Linkage Summary • Linked genes tend to be inherited together in their original, parental arrangement. B. Alleles of linked genes can be separated by crossing over (recombination) during meiosis. C. Distance between genes is calculated as 1% recombination = 1 map unit.

50. Sex Determination Sex Chromosomes: homologous chromosomes that differ in size and genetic composition between males and females