Here’s a cheat to figuring out tortie/calico breeding without using punnett squares!
Tortoiseshells are hard! Ginger is codominant AND sex-linked, making it difficult to visualize exactly how it passes in reproduction. It’s not as simple as “mom is __ so baby is __” because of all the chromosomes and the hetero/homozygous and the whatnot. Very complex stuff.
To a geneticist or breeder, it’s not too difficult to draw up some punnet squares...
But not everyone can draw/understand these so quickly with such fluidity. If you’re a writer or artist who just wants to test for genes real quick, going through the process of learning punnett squares and all the correct loci and chromosomes just might not be something you wanna devote time to.
Never fear! I have a cheat for you!
Put the colours that the parents have (not including white or stripes) in their sections, then decide if this is a male or female kit
If the kit is a MALE, simply pick ONE of the mommy’s colours and drag it into the middle. Kit can be any of those colours. In this case, kit can be ginger or black.
BUT if the baby’s a FEMALE, pick ONE of the mommy’s colours and drag in into the middle and drag the daddy’s colour with it.
This kit can either be ORANGE or TORTIE, but notice how she can’t be black! Because the kit’s colours are a mush of the mom’s and dad’s.
Let’s try this with a different pair!
Here, the mother is simply orange and the dad is simply black:
The female kit can ONLY be tortoiseshell - because she needs one colour from both parents! A male kit, however...
Can ONLY be ginger, because he only gets one colour from the mom!
So there’s a friendly letter-free math-box-free way of figuring out tortoiseshells for those of you who either struggle with or just plain don’t care about punnett squares.
disclaimer: this method is intended to make figuring out codominance easier. If your difficulty is due to factors like dilute/chocolate/cinnamon/tabby, then this won’t be of much help to you. This method will only tell you which loci the kit displays but not which specific alleles. For that, you’ll need to do a bit more work!