When crossing an organism that is homozygous recessive for a single trait (aa) with a heterozygote (Aa), what is the chance of producing an offspring with the homozygous recessive phenotype?

50%

Explanation:

if homozygous recessive for a single trait (aa) cross with heterozygote (Aa)

i. e Aa * aa

there F1 offspring will be:

the test cross is show below

A a

a Aa aa

a Aa aa

= (Aa, Aa, aa, aa)

the results shows 50% heterozygote and 50% homozygous recessive phenotype.