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

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

32. 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)

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

34. 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?

35. Is there an easier way???

36. Product RuleProduct Rule  Make a simple 4 square cross for each trait, then multiply the results for each PPPp pp Rr rr TT Tt

37. 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

38. Example: Lab Fur ColorExample: Lab Fur Color  2 genes are responsible for fur color:  Black gene  Brown-blonde gene

39. Example: Hair ColorExample: Hair Color  2 genes are responsible for hair color:  Black gene  Brown-blonde gene  Black is epistatic (dominant) over the red-blonde gene

42. Polygenic InheritancePolygenic Inheritance  Most traits (especially visible ones) are due to the interaction of multiple proteins, thus multiple genes  As such, most traits do not follow simple Mendelian ratios