Question

In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

A) 1
B) 1/2
C) 1/4
D) 1/6
E) 0

Answer 1

The answer is E) 0.

If:
A - dominant allele,
a - recessive allele,

then:
AA - dominant homozygous (tall),
aa - recessive homozygous (short),
Aa - heterozygous (tall).

A heterozygous plant (Aa) is crossed with a homozygous tall plant (AA):

Parental generation: Aa x AA
F1 generation: AA AA Aa Aa

All of the offspring is tall (AA or Aa), since tall is dominant to short.
There is no chance for offspring to be short (aa).