Question

if you cross two heterozygous parents (aa x aa), what percent of offspring will also be heterozygous (aa)?
a 50%
b 75%
c 100%
d 25%

Explanation:

Step1: Set up Punnett - square

The possible gametes from each parent (Aa) are A and a. The Punnett - square will be a 2x2 table with A and a along the top and A and a along the side.

	A	a
a	Aa	aa

Step2: Count genotypes

There are 4 possible genotypes in the offspring: AA, Aa, Aa, aa.

Step3: Calculate percentage of heterozygous

The heterozygous genotype is Aa. There are 2 Aa genotypes out of 4 total genotypes. The percentage is $\frac{2}{4}\times100\% = 50\%$.

Answer:

A. 50%