Plant A and Plant B are heterozygous for a gene that expresses their tall trait (Tt). Upon crossing, what is expected in the offspring, assuming random chromosome segregation?

The answer is 75% of offspring will be tall and 25% of offspring will be short.

If:

T - the dominant allele for tall trait

t - the recessive allele for short trait

Then:

TT - dominant homozygote (tall)

Tt - heterozygote (tall)

tt - recessive homozygote (short).

In the cross of two heterozygotes Tt x Tt 75% of offspring will be tall and 25% of offspring will be short:

Parental generation: Tt x Tt

Offspring generation: TT Tt Tt tt

Thus, 3 out of 4 (=3/4=75%) offspring are tall (1 TT and 2 Tt) and 1 out of 4 (=1/4=25%) offspring is short. Speaking of genotypes, 1 out of 4 (=1/4=25%) is dominant homozygote (TT), 2 out of 4 (=2/4=50%) is heterozygote (Tt), and 1 out of 4 (=1/4=25%) is recessive homozygote (tt).