Why Are Tricolors Female? The Magical Orange Gene
It’s basic genetics that when a female egg (X) and a male sperm (Y) make a baby, you either get XX (female) or XY (male). That’s simple. But when coat colors of cats get involved, it gets all funky. There is a color gene for orange coloring in cats that is noted as O. The O gene can only be carried on the X chromosome. Since a male cat has only one X chromosome, if he carries the orange gene, he is either OY (orange) or oY (some other non-orange color). Female cats have two X chromosomes, which means they can be OO (dominant orange), oo (recessive orange, which results in the cat being some other color), or they can be Oo, which is tricolor. Tricolor contains both dominant and recessive orange genes.
The O gene is crazy; if you have a dominant O and a recessive o, they combine their efforts. So genetically your tortie is actually orange and not orange at the same time for a phenomenon referred to as mosaic. If that sounds weird, that’s because it is.