Dihybrid crosses

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Dihybrid Crosses:

Tongue rolling (T) is dominant and free ear lobes (E) is dominant. Predict the phenotypes and genotypes of the F1 population for each below.

1. Both Mom and Dad are heterozygous for both traits. (Example done as a class - see below)
Answer: F1 = (Mom)x(Dad)

= (TtEe)x(TtEe)

= (0.25TE + 0.25Te + 0.25tE + 0.25te)x(0.25TE + 0.25Te + 0.25tE + 0.25te)

= (0.0625TTEE + 0.0625TTEe + 0.0625TtEE + 0.0625TtEe +

0.0625TTEe + 0.0625TTee + 0.0625TtEe + 0.0625Ttee +

0.0625TtEE + 0.0625TtEe + 0.0625ttEE + 0.0625ttEe +

0.0625TtEe + 0.0625Ttee + 0.0625ttEe + 0.0625ttee

=9(0.0625T_E_) + 3(0.0625T_ee) + 3(0.0625ttEe) + 0.0625ttee



Phenotypes = 56.25% tongue rolling and free earlobes, 18.75% tongue rolling and

attached ear lobes, 18.75% no tongue rolling and free earlobes, and 6.25% no tongue rolling and attached earlobes


2. Dad is homozygous dominant for tongue rolling and heterozygous for ear lobes. Mom is homozygous recessive for both traits.

3. Dad is heterozygous for both traits. Mom is heterozygous for tongue rolling and homozygous dominant for ear lobes.