Morphs - single gene or polygenic?

[Kleppy]

I have a basic understanding of genetics but I'd like to learn more about the inheritance of colour in ball pythons. Is the morph determined by multiple genes? For example to produce a bumblebee butter - as a bumblebee is a combination of spider and pastel (one parents genetics) and the butter is the other parent, then how can any offspring inherit all three genes from the parents to become a bumblebee butter? And then, if spider is the dominant gene, why aren't the offspring only spiders?


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[Marrissa]

In a bumblebee you have two genes: spider and pastel. A queen bee is that plus lesser/butter. Spider, pastel, and lesser/butter are all 50/50 chance at getting passed on. The only way to get 100% offspring of the same gene (like all pastels) is to have a homozygous (also known as super in the herp world) parent. There are no known super spiders. Spider is a dominant gene, when it gets passed on and you only have a 50/50 shot at it getting passed on.

When pairing a bumblebee to a lesser/butter you'd need to hit the 50/50 odds on all those genes to get a queen bee. You'd have a 1/8 shot at a queenbee.

[OhhWatALoser]

the sticky at the top of this sub forum explain a lot of this, but heres a quick answer

recessive, co-dom/inc-dom, dominant are just classifications for genes based on their phenotype (basically what it looks like), they mean nothing with inheritance.

genes come in pairs, we call the place where a pair of gene sits a locus. if the two genes are the same at a locus, we call it homozygous, if they are different we call it heterozygous.

With your example pastel spider and butter are all on different loci, they all also are heterozygous, each morph gene is paired with a normal gene.

When baby snakes are being made, each parent gives 1 part of each loci to the baby, 50% chance of one gene or 50% chance of the other. so when a bumblebee breeds to a butter, the bumblebee has a 50% chance of giving a pastel gene and a 50% chance of giving a spider gene. The butter parent can only give normal genes for those loci. Now the butter has a 50% chance of giving a butter gene, the bumblebee can only give normal gene for that locus. So if all morph genes are given, there is a chance for heterozygous pastel, spider, butter aka queenbee.

The term dominant is horribly misused and misunderstood by a lot of the ball python community, Forget what you learned in school.... or read in a book..... or heck even googled, it's definition is now "not recessive"

[Kleppy]

Cool thanks. That makes a bit more sense. I was looking at it like the pic... I'll look for the stickie and read a bit more.


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[OhhWatALoser]

you need to include normal from each locus, I always did squares by listing each combination a parent could give, Upper case = morph, lowercase = normal

	SPb	Spb	sPb	spb
spB	SsPpBb	SsppBb	ssPpBb	ssppBb
spb	SsPpbb	Ssppbb	ssPpbb	ssppbb

	SPb	Spb	sPb	spb
spB	Queenbee	Butterbee	Pastel Butter	Butter
spb	Bumblebee	Spider	Pastel	Normal

[paulh]

Bumblebee x butter (AKA lesser) is a three gene pair problem. Each gene pair has its own locus. Each parent gives one gene from each gene pair to each baby, which reestablishes the gene pairs in the baby.

Think of it like this: John has a plate of cookies. Half the cookies are sugar and half are raisen cookies. John flips a coin. If it is heads, you get a sugar cookie. If it is tails, you get a raisen cookie. Mary has a similar plate of cookies and a similar coin. She flips the coin. If it is heads, you get a sugar cookie. If it is tails, you get a raisen cookie. You wind up with two cookies. Both could be sugar, both could be raisen, or one could be sugar and the other raisen. That's how a single gene pair works.

A boa constrictor has over twenty thousand pairs of genes. Unless otherwise specified, we assume that every gene pair is made up of two copies of the normal gene for that locus. In this problem, three gene pairs are specified.

List of genes:
S = spider mutant gene
s = the normal version of the spider gene. (Normal means the gene most commonly found in the wild population.)

P = pastel mutant gene
p = the normal version of the pastel gene.

B = butter mutant gene
b = the normal version of the butter gene.

S P does not make a gene pair. Possible gene pairs are SS, Ss, ss; PP, Pp, pp; and BB, Bb, bb.

Butter parent has these gene pairs: ss pp Bb.
Bumblebee parent has these gene pairs: Ss Pp bb.

Hope that helps.

[Kleppy]

Thanks. That does help. I knew that only one characteristic per locus could be inherited. That's what was confusing me. Makes sense now!


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[Pythonfriend]

thats something special about ball pythons.

there is a background of "normal" genetics, for example, people like to use light-colored reduced pattern normals.

but apart from that, its all individual genes and combinations of these individual genes.

when breeding leopard geckos and corn snakes, you have polygenetic traits where you line-breed for a certain visual result, and also morphs that depend on a single gene. and when breeding dogs or pigeons or horses, its basically all about polygenetic traits.

and yes, the definitions in BP breeding are a bit off.

dominant = when bred to a normal, half of the offspring gets the gene. there is no super form, or at least not a visual one.
codominant = you get a visual difference when a BP has one copy of the gene. but a BP can also have two copies of the gene, which makes it a super form, and that super form looks different. incomplete dominant would be more precise.
recessive = if you only have one copy of the gene, you dont see a difference, or you only have subtle indications that it might be in there. you need two copies for a visual difference.

spider is dominant, pastel and lesser are codominant. when you breed a spider or a pastel or a lesser to a normal, you get 50% normals and 50% single-gene morphs. all 3 genes are independent.

(thats another thing in ball pythons: we have gene complexes, several genes that sit on the same location and strongly interact, and a ball python can only have two of them, or one of them as a super form. for example, butter/lesser, mojave, bamboo, mystic/phantom, special, mocha, and het daddy form the blue-eye leucistic gene complex, many combos will be all white with blue eyes, but there are combos that are not white like mystic potion, purple passion, crystal, leche, platty daddy, super mojave.)

i calculate things in a linear method. in this case, we have 3 genes involved, all independent, one copy of each.

so i start with 100% normals, and throw the first gene at it. one copy of spider. so i get 50% spider, 50% normals. next gene, pastel, i add it in. 25% bumble bee, 25% spider, 25% pastel, 25% normals. now i add lesser to the mix. 12.5% lesser bumble bee, 12.5% bumble bee, 12.5% lesser spider, 12.5% spider, 12.5% lesser pastel, 12.5% pastel, 12.5% lesser, 12.5% normals.

and then i sort it by number of genes:
12.5% lesser bumble bee <--- 12.5% chance to get a triple gene
12.5% bumble bee, 12.5% lesser spider, 12.5% lesser pastel <--- 37.5% chance to get a 2-gene combo
12.5% spider, 12.5% pastel, 12.5% lesser <--- 37.5% chance to get a single gene morph
12.5% normals <--- 12.5% chance to get a normal

it gets a bit more complicated and there are things to consider when super forms and recessives are involved, but the method still works: you start with normals, and add one gene (or gene complex) at a time to the mix. its much faster than making a punnett square. and i did it so often that i dont need to write down the steps in between when its less than 3 or 4 genes, i do it in my mind and then just write down the results.

[paulh]

Yes, the definitions commonly used in BP breeding are a bit off. Here are definitions closer to standard genetics definitions.

When there are two possible forms of a gene, the mutant form and the normal form, there are three possible gene pairs -- 2 mutant genes, 2 normal genes, and a mutant gene paired with a normal gene (making a heterozygous gene pair). Two mutant genes produce the full mutant appearance. Two normal genes produce the normal appearance. The appearance of the animal with the heterozygous gene pair determines whether the mutant gene is dominant, codominant or recessive to the normal gene.

dominant = The animal with the heterozygous gene pair looks like the animal with two mutant genes. There is no visual super form. When the animal with the heterozygous gene pair is bred to a normal, half of the offspring get the mutant gene in a heterozygous gene pair. When the animal with 2 mutant genes is bred to a normal, all the babies have a heterozygous gene pair.

codominant = you get a visual difference from normal when a BP has one copy of the mutant gene (in a heterozygous gene pair). But a BP can also have two copies of the mutant gene, which makes it a super form, and that super form looks different from both normal and the animal with the heterozygous gene pair. In other words, the animal with the heterozygous gene pair can be distinguished from both the animal with 2 mutant genes and the animal with 2 normal genes. For a breeder, incomplete dominant and codominant are synonyms. Codominant has fewer letters so is easier to type.

recessive = if you only have one copy of the mutant gene (in a heterozygous gene pair), you don't see a difference from normal, or you only have subtle indications that it might be in there. You need two copies for a visual difference. This is the mirror image of a dominant mutant gene.

Spider is not recessive. Nobody has identified a snake with 2 spider genes, so we do not know whether it is a dominant or codominant to the corresponding normal gene. All known spider ball pythons have a spider mutant gene paired with a normal gene. Pastel and lesser are codominant.

Pythonfriend uses a tree method to calculate breeding results. So do I, but I prefer to use fractions instead of percentages. It all comes out the same in the end, whichever method is used. The tree method is illustrated near the bottom of the Punnett square entry in wikipedia. http://en.wikipedia.org/wiki/Punnett_square

[whatsherface]

you need to include normal from each locus, I always did squares by listing each combination a parent could give, Upper case = morph, lowercase = normal

	SPb	Spb	sPb	spb
spB	SsPpBb	SsppBb	ssPpBb	ssppBb
spb	SsPpbb	Ssppbb	ssPpbb	ssppbb

	SPb	Spb	sPb	spb
spB	Queenbee	Butterbee	Pastel Butter	Butter
spb	Bumblebee	Spider	Pastel	Normal

Thanks so much for this! I couldn't quite figure out how to do Punnett Squares for bps when I was trying to explain the basic genetics to my sister. I'm a very visual person, so this works better for me than the more mathematic methods.