Basic Genetics

Okay, before we go too far, we need to know some nomenclature and some basic biology.

Co-Dominant: A trait that will be visually expressed with only one copy of the gene, with the caveat that two copies of the gene produces a snake that looks different than one with only one copy of the gene (what we call a "super" form, or homozygous). Pastels are a great example. If only one Pastel gene is present in a snake, it will look like a Pastel. If two copies of the Pastel gene are present, it is a Super Pastel, which looks different than a regular Pastel.

Dominant: Basically, this is the exact same as Co-Dominant except the "super" form (two copies of the gene) looks exactly the same as a snake with only one copy of the gene. Spiders and Pinstripes are good examples of Dominant mutations (though the jury is still out whether they are truly dominant--no need to go into that here). A snake with one Spider gene looks like a Spider; a snake with two Spider genes still looks like a regular ol' Spider.

Recessive: This is where two genes are necessary for the trait to show up visually. You can think of this as a co-dominant trait where the "super" form is apparent but snakes with only one copy of the gene appear normal. (Snakes with only one copy of a recessive gene are called heterozygous, or het for short.) Albinos are a good example of a recessive trait. If you breed an Albino to a normal, all of the offspring will look normal because the offspring only inherited one Albino gene. If you're confused, don't worry; this will become easier to understand when we start doing Punnett squares.

Each parent will pass on half of their genes to each offspring, though which genes get passed on is random. (This is why your brother or sister doesn't look exactly like you; they got a different mix of genes than you despite that you each got half your genes from Mom and half from Dad.) So when we do our Punnett squares later, we need to include two genes for each genetic trait. For example, a normal snake could be labeled as NN: two normal genes, one from each parent. However, a normal can be labeled all manner of ways; I'll talk about that in a sec.

Notice that I labeled the normal NN: two capital Ns. In genetics, a capital letter indicates either a dominant or co-dominant trait. When dominant/co-dominant traits show up, a capital letter combined with a lower-case letter means the dominant/co-dominant trait will override the other lower-case genes. (See why they're called "dominant" now?) Let's use our Spider example from above: A regular Spider can be labeled Ss: one Spider gene, one normal gene (the snake looks like a Spider). If you're wondering why we need two letters, remember that the offspring will get one gene of a certain trait from each parent. Think of it as being in a library, and you have two friends who are each going to give you a book that starts with the letter S. One friend gives you a 1000-page hardback and the other gives you a children's book. You got two books, but you notice the 1000-page book a whole lot more than the kids' book. Each snake parent passed on an "S" book to their offspring, but one of the "books" was the Spider gene and the other book was just some random one in the place where a Spider gene could be. (Did I just completely confuse you? I hope not....)

For recessives, the opposite happens. If a snake only has one Albino gene, we'll label it as Aa, but since the trait is recessive, the lower-case "a" is the Albino gene. A full Albino, then, would be aa, not AA.

What about co-doms? Same thing as doms: Pp is a Pastel, PP is a Super Pastel, pp is a normal.

Other examples:

gg is a Genetic Stripe (recessive), so Gg would be het Genetic Stripe and GG would be a normal.

A Pinstripe (dominant) would be Nn, so nn is a normal and NN is a homozygous Pinstripe (which, since it's a dominant trait, will look the same as a heterozygous Pinstripe).

One more thing: You'll note that I capitalize the names of morphs. Despite my self-imposed Grammar Nazi status, I do not capitalize them because it's grammatically correct (it's actually not). I do this because there are some morphs with generic names, and I feel it is less confusing if morphs are capitalized. For example, someone once asked about Patternless ball pythons. Several of the people who responded didn't realize that Patternless is a specific morph of ball python and thought the person was referring to any morph that lacks pattern (Leucistics, Super Black Pastels, etc.).
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