When two individuals are similar in external appearance but differ in their genetic make up, they are said to have same

The genes are the fundamental unit for carrying the characters from one generation to the other. Genes express themselves and influence the external and internal characters. A phenotype of an individual is the externally visible characters. While the internal change is known as genotype. The change in the genome or genetic makeup of an organism is considered under genotype. So, the correct answer is option A.