DNA and Heredity

Why don't a black cat and a white cat have a gray cat? It has to do with DNA and heredity. DNA stands for Deoxyribonucleic Acid and is a double helix structure made out of 4 amino acids: Adenine, Thymine, Guanine, and Cytosine. DNA holds the instructions for life and is stored in things called chromosomes. Humans have 46 pairs of chromosomes in almost every cell. When parents have offspring, that offspring gets 23 pairs from each parent.

 Let us go back to the question: Why don't a black cat and a white cat have a gray cat? Let's say the cats are purebred. That means the black cat only has genes for black fur and the white cat only has genes for white cat fur. A gene is a unit of heredity. The offspring would have black fur, because the gene for black is dominant. The offspring didn't get white fur because white fur is a recessive trait. The offspring can only have the recessive trait if both parents have that trait.