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Di-Hybrid Crosses

Di-Hybrid Crosses. When two traits are involved in a cross, it is called a di-hybrid cross. Di-Hybrid Crosses. If you want to make a cross of two traits on the same chromosome; you would now need a 4 X 4 square with 16 different possible offspring.

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Di-Hybrid Crosses

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  1. Di-Hybrid Crosses • When two traits are involved in a cross, it is called a di-hybrid cross.

  2. Di-Hybrid Crosses • If you want to make a cross of two traits on the same chromosome; you would now need a 4 X 4 square with 16 different possible offspring. • Here is an example of this larger punnett square.

  3. R = Red fur • r = white fur • X = Long fur • x = short fur • Each parent will always pass a trait for fur color, and a trait for fur length on to the offspring. For the following crosses:use these symbols.

  4. Separating the Gametes • One Parent’s Genotype = RrXx • Use FOIL to separate the gametes. • 1st gamete = RX (first two) • 2nd gamete = Rx (outer two) • 3rd gamete = rX (inner two) • 4th gamete = rx (last two)

  5. Example Problem • Cross a male, heterozygous for both traits. • Genotype = RrXx • with a female that is also heterozygous for both traits. • Genotype = RrXx

  6. Gametes for a Di-Hybrid Cross • Father = RrXx • Possible Gametes are: • RX Rx rX rx • Mother = RrXx • Possible Gametes are: • RX Rx rX rx

  7. RX Rx rX rx RX • Punnett Square for two traits Rx rX rx

  8. Punnett Square for two traits RX Rx rX rx RX RRXX RRXx RrXX RrXx Rx RRXx RRxx RrXx Rrxx rX RrXX RrXx rrXX rrXx rx RrXx Rrxx rrXx rrxx

  9. Genotypic Ratios • RRXX= 1/16 RRXx= 2/16 RRxx=1/16 • RrXX= 2/16 RrXx= 4/16 Rrxx=2/16 • rrXX= 1/16 rrXx= 2/16 rrxx= 1/16

  10. Punnett Square for two traits RX Rx rX rx RX RRXX RRXx RrXX RrXx Rx RRXx RRxx RrXx Rrxx rX RrXX RrXx rrXX rrXx rx RrXx Rrxx rrXx rrxx

  11. Phenotypic Ratios • Red / Long = 9/16 • Red / short = 3/16 • white / Long = 3/16 • white / short = 1/16

  12. Another Di-Hybrid Cross • Cross a male homozygous dominant for both traits. • Genotype = RRXX • with a female who is homozygous recessive for both traits. • Genotype = rrxx • How many different gametes are possible for each parent?

  13. Separating the Gametes • Father = RRXX • Possible gametes = RX • Mother = rrxx • Possible gametes = rx

  14. RX rx RrXx

  15. 100 % of the offspring will be heterozygous for both traits and 100% will have Red, Long Fur

  16. Another Di-Hybrid Cross • Cross a male homozygous dominant for fur color and heterozygous for fur length. • Genotype = RRXx • With a female who is homozygous recessive for fur color and heterozygous for fur length. • Genotype = rrXx • How many different gametes are possible for each parent?

  17. Separating the Gametes • Father = RRXx • Possible gametes = RX Rx • Mother = rrXx • Possible gametes = rX rx

  18. RX Rx rX RrXX RrXx rx RrXx Rrxx

  19. Genotypic and Phenotypic Ratios • Genotypic Ratio • 1/4 RrXX • 1/2 RrXx • 1/4 Rrxx • Phenotypic Ratio • 3/4 Red and Long Fur 1/4 Red, short fur

  20. Assignment 35-3

  21. #1 • Cross two parents that are heterozygous for both traits (TtRr) and give the phenotypic ratio of the expected children.

  22. #1 TR Tr tR tr TR TTRR TTRr TtRR TtRr Tr TTRr TTrr TtRr Ttrr tR TtRR TtRr ttRR ttRr tr TtRr Ttrr ttRr ttrr

  23. #1 Phenotypic Ratios • Tall / Round = 9/16 • Tall / wrinkled = 3/16 • short / Round = 3/16 • short / wrinkled = 1/16

  24. #2 • Cross TTRR with ttrr • Give the phenotypic ratio of the expected children.

  25. #2 TR tr TtRr

  26. #2 Phenotypic Ratios • Tall / Round = 100%

  27. #3 • Cross a TtRr with a Ttrr. • Give the phenotypic ratio of the expected children.

  28. #3 TR Tr tR tr Tr TTRr TTrr TtRr Ttrr tr TtRr Ttrr ttRr ttrr

  29. #3 Phenotypic Ratios • Tall / Round = 3/8 • Tall / wrinkled = 3/8 • short / Round = 1/8 • short / wrinkled = 1/8

  30. #4 • Cross a Round Yellow – heterozygous for both RrYy with a wrinkled green rryy. • Give the phenotypic ratio of the expected children.

  31. #4 RY Ry rY ry ry RrYy Rryy rrYy rryy

  32. #4 Phenotypic Ratios • wrinkled / green = 1/4

  33. Assignment • Di-Hybrid Cross Worksheet

  34. #1 • The genotype for all the F1 offspring will be RrYy

  35. #2 • The phenotype for the F1 offspring will be Round/Yellow

  36. #3 • The cross will be RrYy x RrYy

  37. #5 RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy

  38. #6 • Round,yellow = 9/16

  39. #7 • Round/green = 3/16

  40. #8 • Yellow = 12/16 (3/4)

  41. #9 • green seeds = 4/16 (1/4)

  42. #10 • Pure round, pure yellow = 1/16

  43. #11 • Possible genotypes: EERR, EeRr, EERr, EeRR

  44. #12 • Attached earlobes who can’t roll her tongue = eerr

  45. #13 • Possible genotypes for a person w/ free earlobes who can’t roll her tongue = EErr and Eerr

  46. BS Bs Bs BBSs BBss bs BbSs Bbss

  47. #14 • Black w/ short hair = 1/2

  48. #15 • Red fruit = 3/4

  49. #16 • Green stems & red fruit = 3/16

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