Quote Originally Posted by Andreass View Post
A lethal form doesn't always mean it is co-dominant. It can be that the spider gene carries some "disease". This disease in a heterozygous form might be covered by the remaining normal gene. When a homozygous form is produced the normal gene is absent so the "disease" is lethal. This for example is so with yellow mice.

Actually the ball python genetics of today is way to simple. It is based on genetic laws from the simplest levels. Laws that are made in the 19 th century by Mendel. The majority of the features don't follow such a simple genetic law. This includes the colors of ball pythons.

As we see crossing over is not yet part of ball python genetics. But it is there you can be sure of that. Crossing over happens in every egg and sperm. What the ball python hobby needs are some geneticist how examine every base ball python morph to see how it inherits. A lot of crossing overs will come up togethere with some more complicated forms of gene transfer.
This will result in different chances on offspring.

For example. If crossing over is true for lets say bumblebees. This means that the 25% chance of a bumblebee crossed from a spider x pastel is not correct. The chance will be affected by the physical space between the spider and the pastel gene on a chromosome.

So far we made ball python genetic fits. But the numbers won't be correct for some ( or maybe alot) double gene morphs. Also some things can't be explained cause of this simple genetic laws we follow. So we will need an genetic expert in the hobby who can say what is going on, for example, with the homozygous spider.
I prefer it simple and I dont feel there is a need to get technical with things. Most of us know what the possibilites are when we combine different morphs and that is all that needs to be known as far as I'm concerned.