Answer: A). An allele is one form of a gene.
Explanation: An allele is a different form of a gene. Every trait is usually controlled by a pair of gene, each of the gene is called an allele. For instance, height is a trait and the genes that controls height can be represented as T for tall height and t for short height. T and t are alleles. Alleles can be dominant or recessive. A dominant allele is one which is able to express itself outwardly in the presence of a recessive allele while a recessive allele is one whose effect is masked by a dominant allele. A recessive allele can only express itself when it occurs in a homozygous state.
