Question

which term describes a trait that is only expressed when an organism has two copies of the allele

Answer 1

The term that describes a trait that is only expressed when an organism has two copies of the allele is "recessive." In genetics, a recessive trait will only manifest in the phenotype of an organism when it inherits two copies of the recessive allele, one from each parent. If the organism has one dominant allele and one recessive allele, the dominant trait will be expressed instead.