A Testcross Is Used to ____. ​

A testcross is used to ____. ​

A) determine if a parent with a dominant trait is heterozygous or homozygous
B) determine which allele is dominant ​
C) determine if the progeny of an experimental cross will have a random assortment of alleles ​
D) prove an organism is true-breeding ​
E) cross an individual with a dominant phenotype with a homozygous dominant individual to prove the alleles are dominant ​