The two ​ (a)   received from the parents to control a specific trait are not always expressed. Some alleles are ​ (b)   , meaning they are always expressed in the phenotype. Other alleles are ​ (c)   , meaning they are only expressed when there is no dominant allele. These alleles may remain ​ (d)   for generations and appear in offspring much later.

What percentage chance is there that one of the offspring will be heterozygous dominant?

(a)  

We all have two alleles, or versions, of each gene. Being ​ (a)   for a particular gene means you inherited two identical versions. It's the opposite of a ​ (b)   genotype, where the alleles are different. People who have recessive traits, like blue eyes or red hair, are always homozygous for that gene.

​ (a)   are always expressed when the connected allele is dominant, even if only one copy of the dominant trait exists. ​ (b)   are expressed only if both the connected alleles are recessive.