dihybrid crosses Flashcards
(13 cards)
dihybrid
Crossing two traits simultaneously
step 1
Determine the genotypes of the parents
What are the TWO traits involved?
What is the dominant and recessive phenotype?
What letters will you use?
example: Determine the genotype of the mother. She is heterozygous for big brain and for big toes.
What are the TWO traits involved?
Brain size and toe size
What is the dominant and recessive phenotype?
Brain size: big is dominant, little is recessive
Toe size: big is dominant, little is recessive
What letters will you use?
Brain size: B, b
Toe size: T, t
example: Determine the genotype of the mother. She is heterozygous for big brain and big toes.
BbTt
example: Determine the genotype of the father. He is heterozygous for big toes and he has a tiny brain.
bbTt
step 2: determine the gametes each parent could give using FOIL (First, Outer, Inner, Last)
AaBb -
1 first set - AB
2 outer set - Ab
3 inner set - aB
4 last set - ab
mothers genotype: BbTt
BT Bt bT bt
fathers genotype bbTt
bT bt BT bt
step 3: Line up the possible gametes on a 4 x 4 Punnett square.
see notes
genotype ratio
you must account for every unique genotype. if possible reduce the ratio
A woman is heterozygous for eye color, and is albino (a recessive trait related to skin pigmentation). A man has blue eyes and is heterozygous for skin pigmentation. What percentage of their children will be blue-eyed and heterozygous for normal skin pigmentation? Use E for eye color and P for skin pigmentation.
Step 1: Determine the genotypes of the parents.
woman: Eepp man: eePp
Step 2: Determine the gametes each parent could give by using FOIL.
woman: Ep Ep ep ep Man: eP ep eP ep
Step 3: Line up the possible gametes on a 4 x 4 Punnett square.
Step 4: Work the Punnett square and determine the genotypes & phenotypes
answer 25%
