In a population of ground hogs, there are 45 dark brown individuals that are A1A1, 20 individuals that are light brown and A1A2, and 25 individuals that are light brown and A2A2. Which allele is dominant

A2

Explanation:

According to Mendel's law of inheritance, dominant allele is the one which gets expressed even in heterozygous condition. It is able to mask the effect of recessive allele.

Here, A1 is responsible for dark brown color and A2 is responsible for light brown color. In homozygous condition, both the alleles show their respective phenotypes. However, in heterozygous condition (A1A2), light brown color is expressed. Since light brown color is due to A2 allele, it is the dominant one.

"do a testcross with a homozygous recessive plant."