Genetics... a quick explanation

This is pretty basic stuff, but I needed to give a quick explanation to a friend that was confused (why Spiders are dominant and Pastels aren't) so I figured I'd post my explanation.

A side note:
* Genes come in "pairs", called alleles, they get one from both parent. When we talk about "hets" we are speaking of animals where one gene is "normal" and the other is mutated. Whereas, in homozygous animals, both genes are mutated.

* So it logically follows that breeding a homozygous ball python to any other ball python will produce 100% heterozygous offspring for that animal.

Simple Recessive

Heterozygous - The animal carries the gene, but has no visible mutation (it appears normal). Example: het Albino, het Piebald.

Homozygous - The animal carries the gene, and appears as a visible mutation. Example: Albino, Piebald.

Recessive traits require that both genes be mutated for the mutation to be visible. This is where the term "het" is typically used.

Codominant

Heterozygous - The animal carries the gene, and appears as a visible mutation. Example: Pastel, Woma.

Homozygous - The animal carries the gene, and appears as a visible mutation that is distinctly different from its heterozygous form. Example: Super Pastel, Super Woma.

It is important to note, the "Super" versions of codominant genes are not true dominant genes, which will be explained below.

Dominant

Heterozygous - The animal carries the gene, and appears as a visible mutation. Example: Spider.

Homozygous - The animal carries the gene, and appears as a visible mutation with no visible differences in comparison to its heterozygous form. Example: Spider.

True dominant genes will always appear the same, whether it's heterozygous or homozygous.

Pastels have brighter colors and blushing, Super Pastels have the same, just more of it. The reason why is simple: Pastels exhibit both the "Pastel" gene and the "Non-Pastel" gene, which diludes the mutation. So a "Pastel" could also be called a "het Super Pastel".

If I made a mistake anyone, please let me know :).

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Originally Posted by jhall1468

Pastels have brighter colors and blushing, Super Pastels have the same, just more of it. The reason why is simple: Pastels exhibit both the "Pastel" gene and the "Non-Pastel" gene, which diludes the mutation. So a "Super Pastel" could also be called a "het Pastel".

If I made a mistake anyone, please let me know :).

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that part confused me a bit. Super pastels are the Homozygous form of the pastel morph, so how would a super pastel be a het pastel lol?

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Originally Posted by me

So it logically follows that breeding a homozygous ball python to any other ball python will produce 100% heterozygous offspring for that animal.

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It's probably important to note, that mutations must occur on different gene pairs (alleles). So if you breed a homozygous mutated ball, to another mutated ball, and the alleles for the mutations are the same, it will likely result in bending space-time... or the slightly more likely fact, you won't get any babies (that are alive anyway).

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Originally Posted by bpkid

that part confused me a bit. Super pastels are the Homozygous form of the pastel morph, so how would a super pastel be a het pastel lol?

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Dangit... I read it twice too... lemme fix it.

much better... lol!

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Originally Posted by jhall1468

It's probably important to note, that mutations must occur on different gene pairs (alleles). So if you breed a homozygous mutated ball, to another mutated ball, and the alleles for the mutations are the same, it will likely result in bending space-time... or the slightly more likely fact, you won't get any babies (that are alive anyway).

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One corretion Genes/alleles occur in a locus and can be shared by other alleles that are are co-com ie. Montly and stripe corns the montly allele (gene pair) shares the same locus as the stripe allele. This makes it possible for a snake to be het for both Montly and stripe though, the montly gene is Dom to stripe thus the snake will look like a montly.

the Pastel gene has it's own locus but the gene is co-dom to normal thus showing a partial effect on the snake.

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Originally Posted by titus

One corretion Genes/alleles occur in a locus and can be shared by other alleles that are are co-com ie. Montly and stripe corns the montly allele (gene pair) shares the same locus as the stripe allele. This makes it possible for a snake to be het for both Montly and stripe though, the montly gene is Dom to stripe thus the snake will look like a montly.

the Pastel gene has it's own locus but the gene is co-dom to normal thus showing a partial effect on the snake.

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The primary purpose was to give a quick introduction, and mostly to correct the highly INCORRECT information about dominant/codominant genetic mutations out there.

Has the Montly/Stripe thing been proven out (ie, breed out to produce both Montlys and Stripes but completely unable to produce homozygous Montlys and Stripes?)

Montly and stripe have been proven to share a locus though hom Montlys would be produced from Montly het.stripe x Montly het.stripe pairrings it would be inpossible to say which are hom Montly and Montly het. stripe. There is some work that shows that Cube may actualy also share the same locus.

I reread it and now I see what your saying. Which is why I noted that the mutations must occur on different alleles, not different loci. While different alleles can share the same loci, mutations cannot share the same allele (ie if the same gene pair that mutated the look of the piebald, also mutated the look of the snow, the two would be incompatible).

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Originally Posted by jhall1468

I reread it and now I see what your saying. Which is why I noted that the mutations must occur on different alleles, not different loci. While different alleles can share the same loci, mutations cannot share the same allele (ie if the same gene pair that mutated the look of the piebald, also mutated the look of the snow, the two would be incompatible).

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I see what your saying but also the mistake. The Allele is the actual gene pair in a loci, they do not have to be matching genes to be an allele though in most cases are. Co-doms such as Pastels have non matching genes in their allele (ie if normal is AA and Super Pastel is PP then the allele for Pastel is AP.) Incombatible genes come up when both genes share a Loci but are both recessive. (ie two forms of Amel aa we'll call type one and bb is type b. When bred you would have a allele of ab both genes are recessive to normal and to each other so you end up with a normal).

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Originally Posted by titus

I see what your saying but also the mistake. The Allele is the actual gene pair in a loci, they do not have to be matching genes to be an allele though in most cases are. Co-doms such as Pastels have non matching genes in their allele (ie if normal is AA and Super Pastel is PP then the allele for Pastel is AP.) Incombatible genes come up when both genes share a Loci but are both recessive. (ie two forms of Amel aa we'll call type one and bb is type b. When bred you would have a allele of ab both genes are recessive to normal and to each other so you end up with a normal).

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An allele is not a gene pair. An allele is an allele! An allele is a verison of a gene. Vetebrates are dipolid meaning that they carry a pair of each chromosome. Genes are found at specific spots on those chromosomes called gene loci. For every gene then you have two copies....one copy or allele residing on the maternally inherited chromosome, the other allele residing on the paternally inherited chromosome.

In practice, the term gene pair and genotype are used almost synomously.

You can carry only two alleles for each gene this is where the adjectives homozygous and hetrozygous come in..if they are the same your a homozygote...if they are different you are a het...that simple!

Again you can carry only two alleles one you got from mom, one from dad.....but in the population of organisms there might be many more than just two verisons of a gene at that locus. Think multiple alleles of the Blood system. There's an A allele, B allele, and an O allele. But no one can have all three.

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Originally Posted by Mendel's Balls

An allele is not a gene pair. An allele is an allele!

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Check out Mendel laying the smack down on the homies! ROCK ON! :P

-adam

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Originally Posted by Mendel's Balls

there might be many more than just two verisons of a gene at that locus.

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Is this describing, for example, the different lines of axanthics?

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Originally Posted by Rapture

Is this describing, for example, the different lines of axanthics?

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There no easier way to answer you statement than to say it depends!

If you cross the two axanthic lines and get an axanthic (i.e. the lines are compatible) then the lines are alleles or mutations of the same gene .

If cross the two lines and get a normal, then the lines are incompatible....this means that the mutations that produced the axanthic coloration are not in the same gene (i.e. that do not belong to the same gene pair or reside at the same gene locus).

When two mutations are incompatible and result in a normal or wild-type offspring geneticists say that the two mutation complement one another.

Crossing two mutated lines to one another to see if they are part of the same gene is called a complementation test......do a search on here for complementation and on google if you want to learn more....

Many of the axanthic lines have not shown to be compatible....this means they are not alleles.....they are seperate genes whose mutation can lead to axanthic appearance.....(This doesnt mean that the different lines look identical...they just are comparable-looking enough to be group as axanthic)

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THE ABO system is a good example of multiple allele system.....it found in humans....does a multiple allele system exist in ball pythons? Perhaps....but breeding large scale on these organisms is really new.....so we just dont know....and it might exist but not an an in an easily observable morophological trait! More importantly, the only reason why I brought this system up what to demonstrate that an allele is not a gene pair, its a version of a gene!

Hope that helps.

PS>watch out when quoting someone....when you quoted me above you forgot to include the crucial qualifer "in the population of organisms there might be many more than just two verisons of a gene at that locus"

Intended Allele link-->http://www.answers.com/topic/allele

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Originally Posted by Mendel's Balls

An allele is not a gene pair. An allele is an allele! An allele is a verison of a gene. Vetebrates are dipolid meaning that they carry a pair of each chromosome. Genes are found at specific spots on those chromosomes called gene loci. For every gene then you have two copies....one copy or allele residing on the maternally inherited chromosome, the other allele residing on the paternally inherited chromosome.

In practice, the term gene pair and genotype are used almost synomously.

You can carry only two alleles for each gene this is where the adjectives homozygous and hetrozygous come in..if they are the same your a homozygote...if they are different you are a het...that simple!

Again you can carry only two alleles one you got from mom, one from dad.....but in the population of organisms there might be many more than just two verisons of a gene at that locus. Think multiple alleles of the Blood system. There's an A allele, B allele, and an O allele.

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Awesome post Mendel, and although this is getting more complicated then I intended it to, I stand corrected (funny that I post to clear up confusion and spread misinformation myself :)).

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But no one can have all three.

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ABO+

:carrot:

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Originally Posted by jhall1468

Awesome post Mendel, and although this is getting more complicated then I intended it to, I stand corrected (funny that I post to clear up confusion and spread misinformation myself :)).



ABO+

:carrot:

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Thanks...but what did you mean about the ABO+?

ABO system is one allelic group (alleles of the same gene) the Rh+ and Rh- system is another allelic system. They are different genes......both genes, the one for ABO system and the gene for Rh factor control immunogenic properties of human blood however.

Or where you just carrot dancing?

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Originally Posted by Mendel's Balls

Thanks...but what did you mean about the ABO+?

ABO system is one allelic group (alleles of the same gene) the Rh+ and Rh- system is another allelic system. They are different genes......both genes, the one for ABO system and the gene for Rh factor control immunogenic properties of human blood however.

Or where you just carrot dancing?

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Was a bad joke actually... ABO+ blood type based on your points about being unable to have all three alleles for human blood types.

That and the carrot just looked really happy dancing over there...