Question

The mother is really tall (T) and the allele for this particular trait is dominant to the short (t) gene. The fathers phenotype is short (t). What will the genotype and phenotype percentages be for the the F1 generation? (hint: there may be more than one possible answer).

Answer 1

If tall is completely dominant over short, then the mother's genotype is either TT or Tt. The father is short so his genotype is tt.

Crossing TT with tt produces only heterzygous offspring with genotype Tt. Then the genotypic and phenotypic ratios are 0 TT : 1 Tt : 0 tt and 1 tall : 0 short, respectively. As percentages, these would

• geno:   0% TT : 100% Tt : 0% tt

• pheno:   100% tall : 0% short

Crossing Tt with tt on the other hand produces offspring with genotype either Tt or tt with equal probability, so that the geno and pheno ratios are 0 TT : 1 Tt : 1 tt and 1 tall : 1 short. As percentages,

• geno:    0% TT : 50% Tt : 50% tt

• pheno:   50% tall : 50% short