So we have this autosom chromosome number one, and it's homologous autosom chromosome number two. So one of these came from the male parent, and the other one came from the female parent. And notice in this pair, these two autosomal chromosomes are the same size and the same shape, and they carry the genes that code for the same exact types of traits. So we have this gene that codes for, let's say, the hair color. And this gene also codes for the hair color, and these are known as alleles. Now, let's move on to diagram B and diagram C. And these two diagrams, we discuss the sex chromosome pair.