1. Predicting crosses involving two traits
Dihybrid Notes
Predicting crosses involving two traits

2. Individuals have many genes, so genetics problems can be done to determine how more than one trait is inherited at a time. In this note packet, we are going to focus on crosses involving the inheritance of two traits at once.
When you write out the genotype of an individual, there are certain rules to follow.

3. When you write out the genotype of an individual, there are certain rules to follow.
In the genotype, list the genes in the order given in the problem.
Ex. Long fur, L, is dominant to short fur, l. Striped fur, F, is dominant to solid fur, f. A genotype of an individual that is homozygous for both fur length and pattern is LLFF.
Always list the dominant allele first.
Ex. LlFf is correct while lLfF is not.

4. Give it a try:
In pea plants, long stems, L, are dominant to short stems, l. Green pea pods, G, are dominant to yellow pea pods, g.
Record the phenotype of the following individuals based on their genotypes. The first one is done for you as an example.
LlGg The plant has long stems and green pods.

5. LLGG
llGg
llgg

6. LLGG The plant has long stems and green pods.

7. LLGG The plant has long stems and green pods.
llGg The plant has short stems and green pods.
llgg

8. LLGG The plant has long stems and green pods.
llGg The plant has short stems and green pods.
llgg The plant has short stems and yellow pods

9. E. LlGG F. LLgg G. LLGG

10. E. LlGG The plant has long stems and green pods F. LLgg G. LLGG

11. E. LlGG The plant has long stems and green pods F
E. LlGG The plant has long stems and green pods F. LLgg The plant has long stems and yellow pods G. LLGG

12. E. LlGG The plant has long stems and green pods F
E. LlGG The plant has long stems and green pods F. LLgg The plant has long stems and yellow pods G. LLGG The plant has long stems and green pods

13. Set #2
Record the genotype of the following individuals based on their descriptions. The first one is done for you as an example.
An individual that is heterozygous for long stems and has yellow pods Llgg

14. An individual that has short stems and is homozygous dominant for green pods
An individual that is heterozygous for both stem length and pod color
An individual that is homozygous for long stems and has yellow pods

15. An individual that has short stems and is homozygous dominant for green pods llGg
An individual that is heterozygous for both stem length and pod color
An individual that is homozygous for long stems and has yellow pods

16. An individual that has short stems and is homozygous dominant for green pods llGg
An individual that is heterozygous for both stem length and pod color LlGg
An individual that is homozygous for long stems and has yellow pods

17. An individual that has short stems and is homozygous dominant for green pods llGg
An individual that is heterozygous for both stem length and pod color LlGg
An individual that is homozygous for long stems and has yellow pods LLgg

18. An individual that has a short stem and yellow pods
An individual that is homozygous for both long stems and green pods
An individual that is pure breeding for both long stems and yellow pods

19. An individual that has a short stem and yellow pods llgg
An individual that is homozygous for both long stems and green pods
An individual that is pure breeding for both long stems and yellow pods

20. An individual that has a short stem and yellow pods llgg
An individual that is homozygous for both long stems and green pods LLGG
An individual that is pure breeding for both long stems and yellow pods

21. An individual that has a short stem and yellow pods llgg
An individual that is homozygous for both long stems and green pods LLGG
An individual that is pure breeding for both long stems and yellow pods LLgg

22. What gametes are formed in dihybrid crosses?

23. What gametes are formed in dihybrid crosses?
Mendel’s Law of Independent Assortment:

24. What gametes are formed in dihybrid crosses?
Mendel’s Law of Independent Assortment: Genes that segregate independently do not influence each other’s inheritance

25. What gametes are formed in dihybrid crosses?
Mendel’s Law of Independent Assortment: Genes that segregate independently do not influence each other’s inheritance
When there are two genes, each gamete will have one allele for each gene. There are four possible genetic combinations for the gametes.

26. Possibility #1 for AaBb A a Parent Cell AaBb B b Meiosis I a A b B
Meiosis II A a a A B b B b
Gametes

27. Possibility #2 for AaBb

28. Give it a try…
What 4 gametes would an individual with the genotype AaBb make?
What 4 gametes would an individual with the genotype TtMM make?

29. Give it a try…
What 4 gametes would an individual with the genotype AaBb make?
AB, Ab, aB, ab
What 4 gametes would an individual with the genotype TtMM make?

30. Give it a try…
What 4 gametes would an individual with the genotype AaBb make?
AB, Ab, aB, ab
What 4 gametes would an individual with the genotype TtMM make?
TM, TM, tM, tM

31. Remember:
Gametes can’t have two copies of the same gene (same letter), because one copy of the gene is supposed to come from each parent in each gamete.
If you have two of the same genes in a gamete, nondisjunction occurred and the resulting baby from that gamete would have an extra chromosome and some diseases.

32. Crosses Involving 2 Traits or Dihybrid Crosses
L=long stems and l=short stems
G=green pods and g=yellow pods
Cross: GgLl x GgLl
What will the gametes look like? GL Gl gl gL

33. GL Gl gL gl
GgLl
GGLL
GGLl
GgLL GL
GGLl
GGll
GgLl
Ggll Gl gL
GgLL
GgLl
ggLL
ggLl gl
GgLl
Ggll
ggll
ggLl

34. 9 3 3 1 Possible Phenotypes Green pods with long stems
Green pods with short stems
Yellow pods with long stems
Yellow pods with short stems
Phenotypic ratio
9:3:3:1 9 3 3 1

35. Dihybrid problems

36. aaBB: AaBB: AaBb: Aabb:
1. What kinds of gametes would be produced by organisms having the following genotypes?
aaBB:
AaBB:
AaBb:
Aabb:

37. aaBB: aB, aB, aB, aB AaBB: AaBb: Aabb:
1. What kinds of gametes would be produced by organisms having the following genotypes?
aaBB: aB, aB, aB, aB
AaBB:
AaBb:
Aabb:

38. aaBB: aB, aB, aB, aB AaBB: AB, AB, aB, aB AaBb: Aabb:
1. What kinds of gametes would be produced by organisms having the following genotypes?
aaBB: aB, aB, aB, aB
AaBB: AB, AB, aB, aB
AaBb:
Aabb:

39. aaBB: aB, aB, aB, aB AaBB: AB, AB, aB, aB AaBb: AB, Ab, aB, ab Aabb:
1. What kinds of gametes would be produced by organisms having the following genotypes?
aaBB: aB, aB, aB, aB
AaBB: AB, AB, aB, aB
AaBb: AB, Ab, aB, ab
Aabb:

40. aaBB: aB, aB, aB, aB AaBB: AB, AB, aB, aB AaBb: AB, Ab, aB, ab
1. What kinds of gametes would be produced by organisms having the following genotypes?
aaBB: aB, aB, aB, aB
AaBB: AB, AB, aB, aB
AaBb: AB, Ab, aB, ab
Aabb: Ab, Ab, ab, ab

41. 2. In dogs, the allele F results in a dog that fetches and the allele f results in a dog that will not fetch. The allele D results in a dog that sits on command, while the allele d results in a dog that does not sit on command. You cross a male and female that both fetch and sit, and have the genotypes FfDd and FfDd.

42. FD Fd fD fd FfDd FFDD FFDd FfDD FD FFDd FFdd FfDd Ffdd Fd fD FfDD FfDdA.
FfDd
FFDD
FFDd
FfDD FD
FFDd
FFdd
FfDd
Ffdd Fd fD
FfDD
FfDd
ffDD
ffDd fd
FfDd
Ffdd
ffdd
ffDd

43. What is the phenotypic ratio of the offspring? 
What fraction of the offspring will neither fetch nor sit?
What fraction of the offspring will be FFdd? 
What fraction of the offspring will fetch, but not sit on command?

44. What is the phenotypic ratio of the offspring?  9:3:3:1
What fraction of the offspring will neither fetch nor sit?
What fraction of the offspring will be FFdd? 
What fraction of the offspring will fetch, but not sit on command?

45. What is the phenotypic ratio of the offspring?  9:3:3:1
What fraction of the offspring will neither fetch nor sit? 1/16
What fraction of the offspring will be FFdd? 
What fraction of the offspring will fetch, but not sit on command?

46. What is the phenotypic ratio of the offspring?  9:3:3:1
What fraction of the offspring will neither fetch nor sit? 1/16
What fraction of the offspring will be FFdd?  1/16
What fraction of the offspring will fetch, but not sit on command?

47. What is the phenotypic ratio of the offspring?  9:3:3:1
What fraction of the offspring will neither fetch nor sit? 1/16
What fraction of the offspring will be FFdd?  1/16
What fraction of the offspring will fetch, but not sit on command? 3/16

48. In peas, tall plants (T) are dominant to short plants (t)
In peas, tall plants (T) are dominant to short plants (t). Round seeds (R) are dominant to wrinkled seeds (r). Show a cross between a plant with the genotype TtRr and a plant with the genotype TTRR.

49. In peas, tall plants (T) are dominant to short plants (t)
In peas, tall plants (T) are dominant to short plants (t). Round seeds (R) are dominant to wrinkled seeds (r). Show a cross between a plant with the genotype TtRr and a plant with the genotype TTRR.
Possible gametes from TtRr:

50. In peas, tall plants (T) are dominant to short plants (t)
In peas, tall plants (T) are dominant to short plants (t). Round seeds (R) are dominant to wrinkled seeds (r). Show a cross between a plant with the genotype TtRr and a plant with the genotype TTRR.
Possible gametes from TtRr: TR, Tr, tR, tr

51. In peas, tall plants (T) are dominant to short plants (t)
In peas, tall plants (T) are dominant to short plants (t). Round seeds (R) are dominant to wrinkled seeds (r). Show a cross between a plant with the genotype TtRr and a plant with the genotype TTRR.
Possible gametes from TtRr: TR, Tr, tR, tr
Possible gametes from TTRR:

52. In peas, tall plants (T) are dominant to short plants (t)
In peas, tall plants (T) are dominant to short plants (t). Round seeds (R) are dominant to wrinkled seeds (r). Show a cross between a plant with the genotype TtRr and a plant with the genotype TTRR.
Possible gametes from TtRr: TR, Tr, tR, tr
Possible gametes from TTRR: TR, TR, TR, TR

53. TR Tr tR tr A.
TtRr
TTRR
TTRr
TrRR TR TR TR TR

54. What fraction of the offspring will be TtRr?
What percent of the offspring will be tall with round seeds?

55. What fraction of the offspring will be TtRr? 25%
What percent of the offspring will be tall with round seeds?

56. What fraction of the offspring will be TtRr? 25%
What percent of the offspring will be tall with round seeds?

57. What fraction of the offspring will be TtRr? 25%
What percent of the offspring will be tall with round seeds? 100%

58. Dihybrid practice problems

59. In guinea pigs, short hair (H) is dominant to long hair (h)
In guinea pigs, short hair (H) is dominant to long hair (h). Black eyes (B) are dominant to red eyes (b).

60. In guinea pigs, short hair (H) is dominant to long hair (h)
In guinea pigs, short hair (H) is dominant to long hair (h). Black eyes (B) are dominant to red eyes (b).
Two guinea pigs that are both heterozygous for hair length and eye color are mated.

61. In guinea pigs, short hair (H) is dominant to long hair (h)
In guinea pigs, short hair (H) is dominant to long hair (h). Black eyes (B) are dominant to red eyes (b).
Two guinea pigs that are both heterozygous for hair length and eye color are mated.
What are the genotypes of the parents?

62. In guinea pigs, short hair (H) is dominant to long hair (h)
In guinea pigs, short hair (H) is dominant to long hair (h). Black eyes (B) are dominant to red eyes (b).
Two guinea pigs that are both heterozygous for hair length and eye color are mated.
What are the genotypes of the parents? HhBb

63. HB Hb hB hb HhBb FFDD HHBb HhBB HB HHBb HHbb HhBb Hhbb Hb hB HhBB HhBb

64. What is the expected phenotypic ratio of the offspring
What is the expected phenotypic ratio of the offspring? Be sure to indicate which number corresponds with which phenotype.

65. What is the expected phenotypic ratio of the offspring
What is the expected phenotypic ratio of the offspring? Be sure to indicate which number corresponds with which phenotype. 9:3:3:1  Short hair black eyes: Long hair black eyes: Short hair red eyes: long hair red eyes

66. What is the expected phenotypic ratio of the offspring
What is the expected phenotypic ratio of the offspring? Be sure to indicate which number corresponds with which phenotype. 9:3:3:1  Short hair black eyes: Long hair black eyes: Short hair red eyes: long hair red eyes
What fraction of the offspring have the genotype HHbb?

67. What is the expected phenotypic ratio of the offspring
What is the expected phenotypic ratio of the offspring? Be sure to indicate which number corresponds with which phenotype. 9:3:3:1  Short hair black eyes: Long hair black eyes: Short hair red eyes: long hair red eyes
What fraction of the offspring have the genotype HHbb? 1/16

68. What is the expected phenotypic ratio of the offspring
What is the expected phenotypic ratio of the offspring? Be sure to indicate which number corresponds with which phenotype. 9:3:3:1  Short hair black eyes: Long hair black eyes: Short hair red eyes: long hair red eyes
What fraction of the offspring have the genotype HHbb? 1/16
What fraction of the offspring have the genotype HhBb?

69. What is the expected phenotypic ratio of the offspring
What is the expected phenotypic ratio of the offspring? Be sure to indicate which number corresponds with which phenotype. 9:3:3:1  Short hair black eyes: Long hair black eyes: Short hair red eyes: long hair red eyes
What fraction of the offspring have the genotype HHbb? 1/16
What fraction of the offspring have the genotype HhBb? ¼

70. 2. A guinea pig that is heterozygous for both traits is crossed with a female that has long hair and red eyes.

71. What is the genotype of the female parent?
2. A guinea pig that is heterozygous for both traits is crossed with a female that has long hair and red eyes.
What is the genotype of the female parent?

72. What is the genotype of the female parent? hhbb
2. A guinea pig that is heterozygous for both traits is crossed with a female that has long hair and red eyes.
What is the genotype of the female parent? hhbb

73. HB Hb hB hb B.
hhbb
HhBb
Hhbb
hhBb hb hb hb hb

74. What fraction of the offspring will have the genotype HhBb?

75. What fraction of the offspring will have the genotype HhBb? 1/4

76. What fraction of the offspring will have the genotype HhBb? 1/4

77. What fraction of the offspring will have the genotype HhBb? 1/4

78. What fraction of the offspring will have the genotype HhBb? 1/4
What fraction of the offspring will have short hair and red eyes?

79. What fraction of the offspring will have the genotype HhBb? 1/4
What fraction of the offspring will have short hair and red eyes? 1/4

80. What fraction of the offspring will have the genotype HhBb? 1/4
What fraction of the offspring will have short hair and red eyes? 1/4
What fraction of offspring will have long hair?

81. What fraction of the offspring will have the genotype HhBb? 1/4
What fraction of the offspring will have short hair and red eyes? 1/4
What fraction of offspring will have long hair? 1/2