St. Ann Spay Day

The gene for orange fur in cats is carried on the X chromosome, which is why it’s linked to s*x.

How it works:
Male cats: XY
Female cats: XX

Because the orange gene sits on the X chromosome:
Male cats (XY)
Only have one X, so they can be:
Orange or black

They cannot normally be tortoiseshell or calico, because that requires two X chromosomes with different colours.

Female cats (XX)
Have two X chromosomes, so they can be:
Black
Orange
Tortoiseshell or calico (one X with orange, one X with black)

That’s why:

🧡 Most orange cats are male
🐢 Most tortoiseshell and calico cats are female

Small exception:
Very rarely, a male cat can be tortoiseshell or calico if he has an extra chromosome (XXY), similar to a condition called Klinefelter syndrome in humans. These males are usually sterile.

Picture - credit of The Brain Maze