What is the Greatest Benefit of Having Used a Testcross

Question

What is the greatest benefit of having used a testcross for this experiment?
A)The homozygous recessive parents are obvious to the naked eye.
B)The homozygous parents are the only ones whose crossovers make a difference.
C)Progeny can be scored by their phenotypes alone.
D)All of the progeny will be heterozygous.
E)The homozygous recessive parents will be unable to cross over.

Accepted Answer

The greatest benefit of using a testcross is that progeny can be scored by their phenotypes alone. This allows for easy identification of the genotype of the organism being tested. In this experiment, the geneticist was able to identify the proportions of different phenotypes in the progeny and deduce the genotype of the heterozygous parent. It is not necessary to identify the homozygous recessive parents or their ability to cross over in order to use a testcross.