BIO: Dihybrid Crosses HW
Name: ________________________
Directions: From what you have done so far, you know that you have pairs of genes for all characteristics
and when egg or sperm cells are formed, only one allele from each pair is passed along. As an example, if
a parent has the genes Bb, half the sex cells will have B and half will have b. These are the only
possibilities. If a parent had Bb genes for color and Yy genes for size, there are four possible gene
combinations that could be passed to the offspring. These combinations would be BY, By, bY, by. Look
at the diagram, to see how you get these combinations.
Notice, you never pass along both Bb or Yy. If you did, you would be leaving out genes for the other
characteristic. Do the following dihybrid crosses, using the principles explained above. Remember you
will pass along two genes, but only one from each pair.
Mice – Color and Tail Length
Cross BbLl X BbLl
B = Black
b = White
L= long tail
l = short tail
Parents’ Genotypes: ________________ X __________________
Parent’s Phenotypes ________________________
__________________________
Parent 1 possible allele combinations
________
________
________
________
Parent 2 possible allele combinations
________
________
________
________
Show the dihybrid cross:
Offspring Phenotypes and Ratios:
1. _________________________________________________
2. _________________________________________________
3. _________________________________________________
4. _________________________________________________
2. Cross GGtt X ggTT
G = Green g = yellow
T = tall t = short
Parents’ Genotypes: ________________ X __________________
Parent’s Phenotypes ________________________
__________________________
Parent 1 possible allele combinations
________
________
________
________
Parent 2 possible allele combinations
________
________
________
________
Show the dihybrid cross:
Offspring Phenotypes and Ratios:
1. _________________________________________________
2. _________________________________________________
3. _________________________________________________
4. _________________________________________________
3. In fruit flies, gray body is dominant over black, and straight wings are dominant over curved.
Cross two heterozygous gray, straight winged flies.
Symbols: ____________________
Parent’s Genotypes: ________________ X __________________
Parent’s Phenotypes ________________________
__________________________
Parent 1 possible allele combinations
________
________
________
________
Parent 2 possible allele combinations
________
________
________
________
Show the dihybrid cross:
Offspring Phenotypes and Ratios:
1. _________________________________________________
2. _________________________________________________
3. _________________________________________________
4. _________________________________________________