question about "homozygous spider" vs spider, for example

[SquamishSerpents]

guys i was just playing around with a genetic wizard, and out of curiosity inputted male spider x female spider. the results were 25% normal, 50% spider, and 25% homozygous spider. now, i thought a snake was "homozygous" for something when you could physically SEE the trait. let's just take a snow corn, for example, which is a combination of anery and amel. isn't that snake "homozygous" for amel and anery?

basically i'm wondering why it would be listed as 50% spider and 25% homozygous spider, as opposed to 75% spider?

[MustBeSatan]

My understanding of it is that a homozygous spider, while physically identical to any "het" spider, will produce only spiders when bred to a normal, whereas a het spider will produce only 50% spiders. Of course, the only way to tell whether or not your spider is het or homozygous would be through breeding. Would be a very useful breeder if it was homozygous though!

Someone can correct me if I'm wrong, but I'm pretty sure that's how it works.


EDIT: Also, homozygous doesn't mean simply that the trait is visible, but rather that both allels are the mutated gene, rather than only one (heterozygous). Heterozygous animals with a co-dominant gene do display a physical trait (i.e. Pastel is the het of the homozygous Super Pastel) but dominant genes display even in the het animal, and the "Super" form is an animal which will always produce animals with the mutated trait when bred to a normal. Hope that helps.

[mainbutter]

This will answer all your questions pretty darn well:

http://www.ball-pythons.net/forums/s...ad.php?t=52847

A note: It is suspected that the homozygous form of the spider is fatal, as no one has produced an animal carrying the spider gene that always passes on the spider gene, and there has been no visually different "super spider" produced.

[RandyRemington]

Homozygous and heterozygous are genetic terms describing the genotype of whatever gene location you are talking about. A ball python has two copies of each gene (at least possibly excluding some genes on the W or Z gender chromosomes in females). If the type of those two copies are the same it's the homozygous genotype. It could be homozygous normal or homozygous mutant. If the type is different, it's the heterozygous genotype. A heterozygous ball python could have one normal and one mutant copy or even two different mutant copies (like lesser and mojave) of the gene who’s genotype you are talking about.

So, heterozygous just tells you that the two copies are different which is a very important thing to know about when predicting breeding results because there is a 50/50 chance as to which type (allele) each baby will get from a heterozygous parent. With a homozygous parent you know what it will give each baby because it only has one type.

However, heterozygous and homozygous by it's self doesn't tell you what a mutant will look like. You need to know the mutation type of any mutations involved. If an animal is heterozygous with one normal copy paired with a recessive to normal copy then the animal should look normal (if not the mutation isn't fully recessive). If an animal is heterozygous for a dominant mutation like pinstripe then even one copy of the mutation makes the animal look just as fully pinstripe as two copies in the homozygous pinstripe.

So it's the relationship between how the het mutant with normal looks and how the homozygous mutant looks that defines the mutation type (recessive, co-dominant, or dominant).

Since no one has come forward with a proven homozygous spider yet we still don't know spider's mutation type. We know it's not recessive because the heterozygous spiders are visible mutants (the spider mutant type). If the homozygous spiders are different (like lethal) then spider is a co-dominant mutation.

[SquamishSerpents]

OI YOI YOI i wish i paid attention in biology!

though i must say, i've learned 1000% more about genetics since i started breeding snakes than i ever did in bio!

i'm gonna have to re-read this over tomorrow!