2. Mendelian ExceptionsMendelian Exceptions  Mendel got lucky – all 7 traits he studied showed complete (simple) dominance.

3. Mendelian ExceptionsMendelian Exceptions  Mendel got lucky – all 7 traits he studied showed complete (simple) dominance.  One allele is completely dominant over the other allele  Homozygous dominant and heterozygous = same phenotype  1 allele is enough for full expression of dominant trait

4. Incomplete Dominance = the norm  Heterozygote = intermediate phenotype  1 allele is not enough for full expression

5. Incomplete DominanceIncomplete Dominance  Ex: flower color  R = red RR x rr  r = white

6. Incomplete DominanceIncomplete Dominance  F 2 : Rr x Rr

7. Incomplete DominanceIncomplete Dominance  F 2 : Rr x Rr  Alleles not blended – still able to separate. RR Rr rr 1 red 2 pink 1 white

8. Codominance – Both alleles are expressed equally

9.  Ex: Cows  B = black  W = white  BB = Black  WW = White  BW = ???

10. Codominance – Both alleles are expressed equally  Ex: Cows  B = black  W = white  BB = Black  WW = White  BW = Black and white  Other examples: calico cats, (Stafford sucks), streaked flowers…

11. Multiple allelesMultiple alleles  Allele: Alternate forms of a gene  Only 2 possible alleles in an individual, BUT any # of alleles may be present in a population due to mutations

12. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles

13. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive

14. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AA

15. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA

16. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AO

17. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA

18. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA BB

19. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA BBB

20. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA BBB BO

21. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA BBB BOB

22. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA BBB BOB AB

23. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA BBB BOB ABAB (codom.)

24. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA BBB BOB ABAB (codom.) OO

25. Blood Types (ABO blood types)  Example of simple dominance, codominance, and multiple alleles  Alelles = A, B, O  A & B = Dominant  O = Recessive Genotype Phenotype AAA AOA BBB BOB ABAB (codom.) OOO

26.  Q: What combination of parents have an equal chance of having any of the 4 blood types?

28. Mexican Hairless DogsMexican Hairless Dogs  Hairless (H) is completely dominant over hairy (h).  When two hairless are crossed:  2/3 hairless  1/3 hairy Why???

29. Mexican Hairless DogsMexican Hairless Dogs  Hairless (H) is completely dominant over hairy (h).  When two hairless are crossed:  2/3 hairless  1/3 hairy

30. Lethal AlleleLethal Allele  2 copies of a lethal allele = death (usually stillborn)  Hint: if offspring ratio is x/3, think lethal allele (someone is dying)

31. Lethal AlleleLethal Allele  Q: How can we breed hairless dogs without stillborns?

32. 3, 4, 5, etc. trait crosses3, 4, 5, etc. trait crosses  If a pea plant that is TTRrPp is crossed with a plant that is TtrrPp, what percent of the offspring will be heterozygous for all three traits?

33. Is there an easier way???

34. Product RuleProduct Rule  Make a simple 4 square cross for each trait, then multiply the results for each

35. Epistasis  The process of one gene controlling the expression of another  An epistatic gene can completely mask the effects of another gene  2 genes -> 1 trait

36. Example: Hair ColorExample: Hair Color  2 genes are responsible for hair color:  black-brown gene  red-blonde gene

37. Example: Hair ColorExample: Hair Color  2 genes are responsible for hair color:  black-brown gene  red-blonde gene  Black-brown is epistatic (dominant) over the red-blonde gene  Two “exceptions” present – incomplete dominance and epistasis

38.  B = black  b = brown  R = red  r = blonde -> controls ->

39.  B = black  b = brown  BB__ =  R = red  r = blonde -> controls ->

40.  B = black  b = brown  BB__ = black  R = red  r = blonde -> controls ->

41.  B = black  b = brown  BB__ = black  Bbrr =  R = red  r = blonde -> controls ->

42.  B = black  b = brown  BB__ = black  Bbrr = brown  R = red  r = blonde -> controls ->

43.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ =  R = red  r = blonde -> controls ->

44.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ = auburn  R = red  r = blonde -> controls ->

45.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ = auburn  R = red  r = blonde  bbRR = -> controls ->

46.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ = auburn  R = red  r = blonde  bbRR = red -> controls ->

47.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ = auburn  R = red  r = blonde  bbRR = red  bbRr = -> controls ->

48.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ = auburn  R = red  r = blonde  bbRR = red  bbRr = strawberry blonde -> controls ->

49.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ = auburn  R = red  r = blonde  bbRR = red  bbRr = strawberry blonde  bbrr = -> controls ->

50.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ = auburn  R = red  r = blonde  bbRR = red  bbRr = strawberry blonde  bbrr = blonde -> controls ->

51.  B = black  b = brown  BB__ = black  Bbrr = brown  BbR_ = auburn = breeds true  R = red  r = blonde  bbRR = red  bbRr = strawberry blonde  bbrr = blonde -> controls ->