Genetics Practice: Dihybrid and Backwards
For these problems, use the following key:
G=green seeds
g=yellow seeds
T=tall
t=short
1. Tell the phenotype for the following organisms:
a. Ggtt_________________________________
b. GGTt_________________________________
c. ggtt_________________________________
2. Cross GgTt x ggtt. Make two Punnett squares and tell the phenotypic ratio for
each. Use fractions.
a. What fraction are green and tall?
b. What fraction are green and short?
c. What fraction are yellow and tall?
d. What fraction are yellow and short?
3. Cross GgTt x GgTt. Make two Punnett squares and tell the phenotypic ratio for
each. Use fractions.
a. What fraction are green and tall?
b. What fraction are green and short?
c. What fraction are yellow and tall?
d. What fraction are yellow and short?
4. In corn, tall (T) is dominant to short (t). You see a field of corn and see that half
of it is tall and half of it is short. Use a Punnett Square to show your answer.
5. In corn, tall (T) is dominant to short (t). You see a field of corn and see that 75%
is tall and 25% is short. Use a Punnett Square to show your answer.