Why are Calico cats only females?

Since the gene for fur coloration is attached to the X chromosome, male cats with one X chromosome can only be one color; female cats with two X chromosomes can express both color genes, making them calicos. Each cat receives one X chromosome from its mother and one Y or X from the father.

It is theoretically possible for a cat to have all three chromosomes and become a male calico, but this is extremely uncommon.

Calico cats are almost always female due to the genetic inheritance of coat color. The gene for coat color is located on the X chromosome. Female cats have two X chromosomes (XX), while males have one X and one Y chromosome (XY). In calico cats, the black and orange coat colors are determined by different alleles located on the X chromosome. As a result, female cats with two X chromosomes can express both colors, leading to the distinctive calico pattern. However, males with only one X chromosome cannot inherit both alleles necessary for calico coloring, so calico cats are almost exclusively female.