In garden peas, a single gene controls stem length. The recessive allele (t) produces short stems when homozygous. The dominant allele (T) produces long stems. A short-stemmed plant is crossed with a heterozygous long-stemmed plant. Which of the following represents the expected phenotypes of the offspring and the ratio in which they will occur?
a. 3 long-stemmed plants: 1 short-stemmed plant
b. 1 long-stemmed plant: 1 short-stemmed plant
c. 1 long-stemmed plant : 3 short-stemmed plants
d. Long-stemmed plants only
e. Short-stemmed plants only

The short-stemmed plant would have genotype(tt) and the heterozygous long-stemmed plant would have the genotype(Tt). So when they will cross with each other half of the offspring will be long-stemmed plants and half will be short-stemmed plant.

T t

t Tt tt

So the offspring which have Tt genotype will be tall and the offspring which have tt genotype will be short. Therefore the correct answer is b. 1 long-stemmed plant: 1 short-stemmed plant.