A (lengthy) article on BP Gentics

I wanted to share a rather lengthy article I've written on genetics, specific to ball pythons.

http://ballpython.110mb.com/wiki/index.php/Genetics

I have posted this for a couple of reasons. First, I would appreciate any feedback on the article itself, and second (and perhaps more important) is that the article is released under an opensource license.

What that means, is you can use it on your own site!

A few notes:
If you want to use it, please check the following page:
http://ballpython.110mb.com/wiki/ind...rights:Summary

This will give you the (rather minimal) requirements to use the article. Secondly (and most important) the photos of the snakes themselves are not released under the above license. All the photos are copyrighted, and permission was granted for their use. The graphics, diagrams and other information are released under Public Domain... meaning you can use them in any fashion you want.

As long as you fullfill the obligations listed in the Copyright link above, you are free to use the content, no permission neccesary :).

Again, I would love to receive feedback on the article, especially any errors.

Very nice presentation and thorough!

Without any formal genetics training since high school I do have a few questions.

I've gathered that there have been several competing genetics notations coming from different fields. Is that still the case or is this an agreed upon standard? I see where you used the color coding to distinguish the normal for albino allele “N” from the normal for clown allele “N”. Do you have anything against using the notation where the same letter is used for both variants at a locus of an interesting mutation like “C” for normal for clown and “c” for the clown variant and similarly “A” for normal for albino and “a” for albino? I know this isn’t perfect either and will get more complex as we identify situations with more than 2 possible variants at a locus (like the Platy complex). I’m also unclear how to handle the capitalization in cases of co-dominance. I’m just thinking the common “N” is confusing and color coding might not always be available to keep it straight.

Also, are you aware of any homozygous spiders?

Hi there!

Thanks so much for sharing, since this is a field that combines both my professional abilities and personal interests, I'll review it as if it were one of my student's if you don't mind. If you do... you probably shouldn't read any further! As I'm sure this is something you want read by wider circles, I'll comment on both the writing and the content:

This article seems to be a cross between a well-considered structure and off the top of your head writing. If you truly intend for this article to be a reference you will have to correct the errors, be more specific with your definitions, and prepare the content with more academic rigor. I do like the structure, and you have a firm foundation for the type of writing you wish to produce. Your grammar is better than most people's, though there are typos throughout to correct. Your use of the vocabulary makes me think a good review of a genetic textbook would be a good investment of time. Excellent diagrams and pictures, and while your writing is awkward at times, it isn't too flowery to distract from the information presented. You will want to flesh out certain parts though, as it is unclear, even from the given structure what information will be presented and why. It is a bit too scattered to be considered a wiki just on vertebrate/eukaryotic genetics, and not robust enough to be a wiki on ball python morphs.

Here are some specifics:

"The wide variety of Ball Python morphs available today are possible through genetic mutations. A key to successful breeding is understanding genetics at its very core."
-The first sentence is awkwardly written, and you need a transition into the second sentence. As it stands now they shouldn't be in the same paragraph.

"This article intends to be a de facto reference for explanations of genetic mutations among Ball Pythons."
-That is an uncommon use of 'de facto' and doesn't fit well with the article.
-Awkwardly worded again... article, reference, explanation all a little redundant.

-If you use quotation marks, cite the reference.

"a single gene is [the] fundamental unit of heredity. The act of procreation distributes these genes to the parents' [or parent's] offspring. By receiving the genes from two parents, it widens the gene pool, and allows offspring to [ob]tain unique genetic characteristics from each parent (second parent is redundant)."
-As an introduction for beginners you'll want to indicate new vocabulary with bold or italics and not use them as if they are part of a layman's vernacular.
-In general, the fundamentals of genetics and sexual reproduction have been widely written about. Emulating the style of published literature isn't plagiarism.

"We are already aware that chromosomes come in pairs, and as such, so do genes."
-Are we aware of this already?
-Also, if you think alleles only come in pairs, there is a significant limitation in your knowledge that if addressed will help with the short-comings of the genetic information presented here.

"We can put a number of pots and pans at each of these heating elements, however, each pot and pan has unique characteristics. In this example, the pots and pans are genes and the frying pan and sauce pan are different variations of it, or the alleles."
-Very interesting analogy, is it yours? It works.

"when discussing specific genetics of an individual morph."
-You might want to define morph to give the article a better flow and make it more informative.

"Is is extremely likely that there is a pigment gene, and the "Albino gene" is simply an allele that prevents the creation of melanin."
-What is your source for the "pigment" gene?
-For this to be a truly informative and useful article, you will probably want to investigate the different types of pigment produced by the wild-type, and discuss whether it is a disrupted gene, a disrupted promoter, or an upstream/downstream component of a genetic system that leads to phenotypic expression.

"and aside from that, we simply don't know how many genes are being affected by each charactAristic."
-Simply, because all morphs that have been identified as "genetic" through linebreeding and outcrossing, we know nearly all traits to be simple recessive, simple dominant, or co-dominant... meaning the number of genes involved in yielding any "base" morph is 1.

"a single gene is being mutated in any given morph."
-improper tense, a gene mutation arises, and if in a sex cell is passed onto progeny. All in the past.

"Earlier in the article, we learned that Ball Pythons are diploid..."
-this is the first time you've used "diploid".

"However, where these chromosomes can differ [is] in the alleles they carry."
-Most spellcheckers will detect sentence fragments....
-Also, chromosomes may also differ because of imprinting, meaning the chromosome from the mother can behave differently than the same chromosome from the father.

"During the fertilization process, the offspring retain two cells from the sire and dame"
-retain is "to keep", obtain is "to get".
-this is an inaccurate description of the fertilization process. Two haploid cells join, and their nuclei fuse. Not two cells are obtained...

"its offspring have the potential to [inherit] one of two alleles"

"any given offspring has a 50% chance of inheriting either one of the alleles."
-there's a 100% chance of inheriting either one
-there's a 50% chance of inheriting one over the other, odds is a difficult concept.

"Typically, when referencing specific morphs the morph name alone implies the animal is homozygous. Although, this depends on the allele's phenotype."
-This is the atypical case. Usually it is only a recessive morph that's name is synonymous with homozygous, with pseudo-exceptions like Leucistic.
-alleles cannot have phenotypes, alleles make up a genotype, which gives rise to a phenotype.

"A phenotype is one or more visible characteristic[s] of an organism, caused by a specific allele."
-this is an uncommon definition, that probably won't gain acceptance from an educated audience. The last clause is causing you problems.

"A recessive allele, causes a phenotype that is only visible in the homozygous form. An Albino, for example, is a simple recessive trait."
-Traits are recessive, meaning the allele in question does not have a visible effect unless the 'normal' allele's influence is removed. You'll want to careful when using the term "recessive allele" though this is probably more of a pet peeve.
-generally, "An Albino" would refer to an amelanistic individual, not a trait.

"is prefixed before the morph's heterozygous name"

"A dominant allele, causes a phenotype that is visible in both the heterozygous and homozygous form."
-this definition does not distinguish between dominant and co-dominant. Since you're so intent on using your own definitions for things, incorporate the fact that the homozygous and heterozygous forms are visibly indistinct.

"the only way to prove it is through breeding it to a normal."
-Since all spiders in captivity are descended from one animal (unless this is an urban legend), it will be very easy to tell if a Spider could be homogzygous by its pedigree which would be readily known.
-As well, simple non-specific genetic tests that do not rely on sequence knowledge could determine the zygosity of the 'Spider' locus.

"When more than a single allele is being impacted,"
-impacted by what?
-the rest of this section is some of your better writing.

"an organism with 10, 25, or 100 genetic mutations would make for a very long conversation."
-funny

"A heterozygous Albino may be written as "Na" the capital "N" showing the allele, and the lowercase "a" indicated the Albino allele."
-Randy is absolutely correct on notation. You do not complicate genetic notation by using different letters for the same trait!
-First define your gene, then your notation and give an example:
Trait - Albinism
Gene - Melanin-production protein 1
N - wildtype allele
n - albino allele
A male albino ball python would have the genotype: aaXY

"Regardless of the letters used, just remember if both letters are uppercase, the animal is normal"
-this isn't correct either.
-a 'normal' animal's Pastel locus would be pp, and a Super Pastel: PP

"if both are [of the same] case, it's a homozygote."

"Determining the possible offspring for a dame and offspring"
-what does this mean?

Good work on the Punnett Square, you'll want to fix your notation.

"When breeding a normal ball python to a heterozygous Albino, the results are 50% NN and 50% Na"
-Wrong again!
NN x Na (your notation) yields 25% Na, not 50%.
-You were thinking of breeding NN x aa.

"It is drastically important..."
-unconventional/incorrect use of 'drastically'
-awkward wording of this paragraph.

Coloration of the Punnett Square is quite impossible with "paper and pencil", and needless. I would suggest reworking this suggestion.


Hope this helps!

Wow! People pay a lot of money for that kind of review! That's awesome!!

Great stuff!! That post above us is proably the longest one I have ever seen!:eek:

yeah, I have some skills :P Unfortunately, the university doesn't pay well enough for them!

Like I said, it's something I'm passionate about... and the more articles or pages out there that someone can show a loved one, a friend, a child, etc to educate them and share their passion and knowledge, the better!

The section titled Gene/Allele confusion is very confusing.

"we simply don't know how many genes are being affected by each characteristic"


Not really sure what you mean here.
First of all in traditional genetics genes influence traits, not the other way around.

We know that traditional albinism is caused by one gene. There are other forms of albinism caused by different gene loci. They are usually called something different like lavender albino or caramel albino etc.

It is possible that two different traditional-looking albinos of separate lineages are mutants of different gene loci. But you could easily distinguish these two possibilities by using the recessive complementation test.

If they were slightly different mutations of the same gene-->A1 (a1a1) x A2 (a2a2)-à a1a2 (all Albinos)


If the mutations were of separate gene---> A1 (a1a1 A2A2) x (A1A1 x a2a2)à A1a1A2a2 (A normal looking animal that would be heterozygous for both albino genes)

Furthermore, when a base morph is discovered initially. You can determine whether that particular genetic aberration is caused by one or two genes. For example, let’s say you find a white looking snake. You breed your snow to a normal looking bp (the F1 generation). All offspring in the F1 generation are normal looking. At this point, your putative genetic aberration is either non-genetic, a one gene-recessive, or possibly a multi-gene recessive. You can begin to distinguish among the possibilities by crossing two of the F1 offspring. If after years of nice large clutches you find ~25% of the offspring to be white while ~75% are normal, you’ve found a one gene recessive trait.


Now let’s say you get different results from your F1 x F1 cross. Your amazed that in your first clutch you get a normal looking offspring, albino offspring, and axanthic offspring. Furthermore, after patiently waiting for your F1 parents to be ready to breed again you repeat the cross. This time you get 1 white snake almost identical to the original founding parent. After decades of work and recording keeping you find that you get ~56%(9/16) normals, ~18% albinos (3/16), ~18% (3/16), and 6% (1/16) white looking snakes. This is the classic two gene or dihybrid ratio of 9:3:3:1.

Now the second scenario was made up, but it was based off of the designer morph snow. This is exactly the kind of thing that would happen if you found a snow in the wild and wanted to prove it genetic!

While your unlikely to find a snow or two gene aberrant in the wild, the scenario illustrates that you can distinguish a trait that is caused by one gene from a trait that is caused by two or more genes using classic Mendelian analysis.

One gene recessive-->3:1 phenotypic ratio

Two gene recessive--->9:3:3:1 phenotypic ratio

Wow, this is great! I never expected to receive such a response and I can't be happier with the results. Thank you VERY much for the review Dread, I never expected a professional review to this degree and I was certainly hoping someone much more experience would give it a once over.

A few comments:

Randy and Dread are right on with the Punnett Square. I used different letters and colors to indicate why a double recessive animal would have two "normal" alleles, but in doing so probably created more problems than solutions, since it breaks from tradition.

Mendel, what I was referring to were dependent mutations, but perhaps I should have made that more clear. For example, there seems to be a serious genetic influence in Clowns, that can be bred to reduce the pattern of the side stripes. This to me suggests that there is a second gene at work, dependent on the Clown allele.

Perhaps I am wrong on that, and if so it should be corrected. Again, thank you all for the awesome posts!

I like to thank all you guys Jhall, Dread and Mendel for the crash course in genetics. I know how thw basics of co-dom, dom and recessive works but you guys have really opened a whole new dimension to me on the nuts and bolts of what puts it all together. I saw the thread this morning but didn't have the time to read it but just finished and I'm glad I did. REALLY informative! Thanks! :sunny:

Having trouble posting......not sure why.

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Originally Posted by Dread

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Originally Posted by Dread

"We are already aware that chromosomes come in pairs, and as such, so do genes."
-Are we aware of this already?
-Also, if you think alleles only come in pairs, there is a significant limitation in your knowledge that if addressed will help with the short-comings of the genetic information presented here.

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Are you talking of hemizygous loci like the X and the Y chromosome. OR the Z and W in birds and reptiles? Because pythons are ancestrally primitive snakes they don't have much differentiation between their sex chromosomes so I think it’s fair to say that most of their genes come in pairs.

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Originally Posted by Dread

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Originally Posted by Dread

"A recessive allele, causes a phenotype that is only visible in the homozygous form. An Albino, for example, is a simple recessive trait."
-Traits are recessive, meaning the allele in question does not have a visible effect unless the 'normal' allele's influence is removed. You'll want to careful when using the term "recessive allele" though this is probably more of a pet peeve.
-generally, "An Albino" would refer to an amelanistic individual, not a trait.

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Your being a little "nit-picky" here, Dread.

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Originally Posted by Dread

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Originally Posted by Dread

"A dominant allele, causes a phenotype that is visible in both the heterozygous and homozygous form."
-this definition does not distinguish between dominant and co-dominant. Since you're so intent on using your own definitions for things, incorporate the fact that the homozygous and heterozygous forms are visibly indistinct.

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Again you’re being a little nit-picky here. Overall, the section titled "Types of genes" is pretty good in my opinion.

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Originally Posted by Dread

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Originally Posted by Dread
Coloration of the Punnett Square is quite impossible with "paper and pencil", and needless.

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Coloration is great for educational purposes. I like it.

I do not like the use of the letter N or n for normal. I like to stick with the same letters when talking about alleles of the same gene. This way you know that A and a are alleles of the same gene C and c are alleles of the same gene. You also know something about dominance relationship between the two alleles. You know that C is dominant to c. It may be complete or partial dominance but you know that C is dominant to c somehow.

This is somewhat a matter of preference as different geneticists use different notational systems. For example, Fruit fly (Drosophila) geneticists use a one or two letter symbol system, with a "+" sign. The "+" sign is used to designate the normal or wild-type phenotype.

For example, vg+vg+ would be a normal, vg+vg would be a wild-type, and vg vg would be the phenotypic expression of a recessive mutation. This is real trait by the way-->vg codes for "vestigal" or shortened wings.

Your notational system could work as long as you designate capital "N" and lower-case "n" as alleles of any gene that code for wild-type phenotypes. N could not ever be used to designate a mutant morph. Little n would be used in cases where the mutation coding for the genetic morph is dominant or co-dominant with the wild-type or normal allele.

Notational systems are very specific to the model organism in biology. I see no reason in principle why ball python breeders or reptile hobbyists can not come up with their own variation--as long as it's internally consistent. Though I'm also a fan of using what's not broken!

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Originally Posted by Dread

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Originally Posted by Dread


"However, where these chromosomes can differ [is] in the alleles they carry."
-Most spell checkers will detect sentence fragments....
-Also, chromosomes may also differ because of imprinting, meaning the chromosome from the mother can behave differently than the same chromosome from the father.

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Again you’re being picky again. Though sometimes I can be too picky as well.



But you’re also not being really technically correct according to our best knowledge. Genomic imprinting is known at this time to occur only in mammals. For those of you who don't know, genomic imprinting, or simply imprinting, is the phenomenon where the behavior or expression of a gene depends on the parent of origin. In other words, you can inherit the same piece of DNA from your mom and the same piece of DNA from your dad, but the maternal allele acts differently than the paternal allele. It is called imprinting because the parent leaves a sex-specific imprint or mark on the allele that is transmitted to the offspring. This sex-specific mark is in the form of a chemical modification to DNA, called cytosine methylation. I use to work in a genomic imprinting lab and have a peer-reviewed paper on it in Molecular and Cellular Biology.

Incidentally, I believe that genomic imprinting is unlikely to be found in reptiles. There have been no documented cases of natural parthenogenesis in mammals. The reason behind this is that many mammalian genes and chromosomal segments undergo genomic imprinting. Basically, a mammalian offspring can not be produced when both sets of chromosomes come from the same parent because all loci that are imprinted would have abnormal levels of gene expression.

Now parthenogenesis has been found in many reptiles, the most recent being the Komodo dragon. The occurrence of natural parthenogenesis suggests that imprinting is not a major factor for reptiles. This is because an offspring can be produced from only the female's germ line. This suggests to me that imprinting isn't at work, because viable offspring don't require imprints from the male germ line.

Imprinting is more of a matter of epigenetics than genetics so I would not worry too much about it in an article of ball python genetics.

He may be being nitpicky but for the average joe who knows nothing about ball python genetics this article can be confusing.

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Originally Posted by tmlowe5704

He may be being nitpicky but for the average joe who knows nothing about ball python genetics this article can be confusing.

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And your not being very helpful.

JHall keep working on it.....it will get there.

wow great open source best thing ive read on genetics besides the genetics book i own

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Originally Posted by tmlowe5704

He may be being nitpicky but for the average joe who knows nothing about ball python genetics this article can be confusing.

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Given the fact that there are litterally hundreds of threads between all of the reptile forums that start "What will I get when I cross a..." there isn't exactly a superior resource available for the average Joe anyway.

Fortunately, this forum has at least 2 people with an extrodinary amount of knowledge when it comes to genetics, and hopefully after implementing their suggestions this article will be that much closer to clearing up confusion.

I truly appreciate constructive criticisms thus far, but your comment certainly wasn't constructive. If you would like to point out areas that you feel are incorrect, or could be better, feel free to do so.

Well I've made most of the suggested corrections by Dread and Mendel, and I think it gives the article a little more professional appearance. Although, it still definately needs some work.

Some areas that I didn't make the suggested changes:

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-For this to be a truly informative and useful article, you will probably want to investigate the different types of pigment produced by the wild-type, and discuss whether it is a disrupted gene, a disrupted promoter, or an upstream/downstream component of a genetic system that leads to phenotypic expression.

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I didn't add this information, mostly due to the fact that it does seem readily available. However, I'm not sure that the article itself would benefit from going into that much detail, especially since I'm only using a single example. Perhaps that would be something to go into detail in the respective morph pages, that way each morph has it's own detailed explanation, instead of just hitting on Amelanistics.

I did make the changes to the Punnett Squares as suggested, however, I think my explanation on why simple recessive notation differes from codominant and dominant notation is weak and confusing, and probably needs a serious rewrite. I'm thinking a Punnett Square example with a codominant morph would be more appropriate.

I did, however, leave the colorization intact. I agree with Mendel on this one. The purpose of the article is education, and the examples are intended to show how the individual squares are filled in. By showing the concept with color, I think it will be easier to understand when using pen and paper.

Thanks again for all of the suggestions, they certainly helped in making some really confusing aspects of the article a little more straight-forward, but there is still much to be done :).

"Recessive, codominant and dominant morphs are often referred to as base mutations. This is understood to mean morphs that exist in the wild. Complex types, like the double recessive mutation, is called a designer mutation, in other words, it's highly unlikely that this mutation will occur in the wild."

This needs some work.

Define the concept of a genetic morph.

Then Differentiate between base and designer morph. Designer mutation is rather misleading because most designer morphs have mutations in two separate genes.

Designer mutations make it sound as though the breeder is using mutagenesis to induce mutations in the animal.

See number 8 on this page.

I also think it would be helpful to include a link on these pages to this site.

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Originally Posted by jhall1468

I truly appreciate constructive criticisms thus far, but your comment certainly wasn't constructive. If you would like to point out areas that you feel are incorrect, or could be better, feel free to do so.

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I did not see my post as being offensive or whatever. By Mendel saying dread was being nitpicky, I was just backing up dread saying for the average joe who wants to learn about BP genetics, this could be an excellent resource if you "dumb" it down a bit for someone starting out interest in BP genetics. I know there will never be a best source for genetics info, but I feel this one has the possibility to be one of the best.

a note here for clarity. i just edited mendel's post #11

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Originally Posted by tmlowe5704

I did not see my post as being offensive or whatever. By Mendel saying dread was being nitpicky, I was just backing up dread saying for the average joe who wants to learn about BP genetics, this could be an excellent resource if you "dumb" it down a bit for someone starting out interest in BP genetics. I know there will never be a best source for genetics info, but I feel this one has the possibility to be one of the best.

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I didn't think you were being offensive. I just didn't think you being being helpful...big difference.

As far as backing Dread up...my point was that by Dread being nit picky he wasn't "dumbing it down". Reread my reponses to Dread and I think you'll see what I mean-no need to mention things like imprinting or hemizygous loci in a beginner article. They are too technical.

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Originally Posted by recycling goddess

a note here for clarity. i just edited mendel's post #11

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Thanks for doing that for me.

no problem. tried to pm you letting you know it was done... but your pm box is full! :P

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Originally Posted by recycling goddess

no problem. tried to pm you letting you know it was done... but your pm box is full! :P

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woops time to clear some of those out....:)

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Originally Posted by tmlowe5704

this could be an excellent resource if you "dumb" it down a bit for someone starting out interest in BP genetics. I know there will never be a best source for genetics info, but I feel this one has the possibility to be one of the best.

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That's an area I'm going to have a great deal of difficulty with, which is why I *hope* that newcomers will comment as well, on areas they consider overly technical. Once the article itself is as accurate as possible I'm going to be adding in "hint boxes" here and there to give analogies for the more complicated topics (such as the one used to describe alleles).

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Originally Posted by Mendel's Balls

"Recessive, codominant and dominant morphs are often referred to as base mutations. This is understood to mean morphs that exist in the wild. Complex types, like the double recessive mutation, is called a designer mutation, in other words, it's highly unlikely that this mutation will occur in the wild."

This needs some work.

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I agree... for starters it shouldn't be under the complex types heading so I'll need to play with that anyway.

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Originally Posted by Mendel's Balls

no need to mention things like imprinting or hemizygous loci in a beginner article. They are too technical.

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For the author and the reader :D. I'm really already writing outside of my capabilities, evident by the fact that I made quite a few errors.

This is a beginner article. If someone with a greater breadth of knowledge in genetics chooses to write a followup article on more complex topics, so be it. It's a wiki, so that's what it's designed for, but it certainly won't be written by me ;).

Coming along very nicely!

I’m still having some trouble with the Gene Variations section. Perhaps the wording of the following could be changed a bit:

“However, it's highly unlikely that there is a specific gene which determines whether an animal is Albino or not.”

I believe one of your points is that we shouldn’t refer to the locus where the albino allele has been seen as the “albino gene” because there are also normal for albino and perhaps even other variations possible at that locus. I can see where doing so could lead people to think that albinos have an extra gene that non albinos don’t have, rather than just a different version of that gene. But to me whether you call it the albino gene or the pigment gene is a subtle difference that perhaps needs more explanation for readers to easily pick up the distinction.

How does this sound?

“It is highly unlikely that albino ball pythons are the result of a new albino gene locus (stove element in our analogy) that is not present in normal for albino ball pythons. The gene locus is always there, it’s just that albino ball pythons have a new mutant allele in place of the normal for albino allele, i.e. a new kind of pot is sitting on that element.”

Also, I’m not sure “pigment gene” is a good choice as there are many other color affecting loci that could also be considered pigment genes. You could refer to the gene location as the melanin gene but even that is tricky as there are several incompatible types of albinos in ball pythons so apparently multiple loci effecting melanin. I’m not sure what to call it and that’s probably why we fall back on “albino gene” to refer to the locus but I see where that can be confusing too.

Also, you should know that there doesn’t seem to yet be a publicly demonstrated example of a dominant ball python mutation type. Spider and pinstripe are both candidates but neither has yet seen a proven homozygous animal unveiled. It’s possible that spider is homozygous lethal which I think would technically be co-dominant. I would imagine that we eventually will have a proven dominant morph (spider might yet be the first) and agree that the subject should be covered but you might want to qualify your spider example.

Well, I made some major adjustments to the TOC, and kind of implemented Randy's suggestion. I didn't do it exactly as you said to, but I agree that the pigment gene example was weak at best.

I also implemented some changes to the "types of morphs" and removed the term "morph" altogether before discussing what the "base" and "designer" mean. I felt it was neccesary to understand what a phenotype was before introducing the term morph.

Hopefully some time in the next day or so (maybe tonight if I'm not too lazy ;)) I'm going to do a codominant/dominant example in the Punnett Squares section.

I also added in an editor's note pointing out that a homozygous Spider has yet to be produced. Hopefully that will change soon :).

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Originally Posted by RandyRemington

It’s possible that spider is homozygous lethal which I think would technically be co-dominant.

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I really know how that would work, but I'm going to try to talk to our genetics professor later today and find out.

Actually a homozygous spider may have been produced; it's just that I’ve not seen anyone publicly claiming to have one yet 7 years into captive bred spiders. Hard to tell if that's because it really hasn't been produced (perhaps because not viable), hasn't had time to be proven homozygous through breeding yet, for some marketing reason (would it hurt or help spider prices?), or because homozygous spiders are in some way not publicly presentable.

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Originally Posted by RandyRemington

Actually a homozygous spider may have been produced; it's just that I’ve not seen anyone publicly claiming to have one yet 7 years into captive bred spiders. Hard to tell if that's because it really hasn't been produced (perhaps because not viable), hasn't had time to be proven homozygous through breeding yet, for some marketing reason (would it hurt or help spider prices?), or because homozygous spiders are in some way not publicly presentable.

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It probably has more to do with the fact that since homozygous spiders don't look any differently than heterozygous spiders, most people out there don't want to look like a boob when the "homozygous" spider they claimed to have sires a clutch of normals.

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Originally Posted by RandyRemington

Actually a homozygous spider may have been produced; it's just that I’ve not seen anyone publicly claiming to have one yet 7 years into captive bred spiders. Hard to tell if that's because it really hasn't been produced (perhaps because not viable), hasn't had time to be proven homozygous through breeding yet, for some marketing reason (would it hurt or help spider prices?), or because homozygous spiders are in some way not publicly presentable.

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True, but for the sake of the article I don't think any assumptions should be made. We look at the Banana, Pinstripe and Spider and no one has come out and said "I've produced a homozygous XXXXX". Then again, I think a LOT of people are too busy producing crosses to bother with such things. Even Super Pastels still seem to be relatively rare on the market.

With the popularity of Bee's these days, I imagine most people aren't breeding heterozygous Spiders together all that often. Although I'm sure the big breeders have... and if anyone has spiders it's them.

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Originally Posted by elevatethis

It probably has more to do with the fact that since homozygous spiders don't look any differently than heterozygous spiders, most people out there don't want to look like a boob when the "homozygous" spider they claimed to have sires a clutch of normals.

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But until someone's possible homozygous spider produces a bunch of only spiders we don't know for sure what homozygous spider look like. It's really hard to prove something by its absence. Just as I can't say for sure that spider is homozygous lethal by the absence of a publicly proven homozygous spider you can't say for sure it's dominant because of the absence of a publicly disclosed different looking potential homozygous spider.

What if it turns out that the homozygous eggs do hatch and produce a different looking or acting snake but it doesn't thrive and can't be bred to prove it's homozygous? With other potentially homozygous lethal morphs we've assumed a radically different looking animal is the homozygous without proving it so we could still reach closure on the spider genetics eventually. But what if the homozygous is only subtly different from the heterozygous ones but still consistently different and not capable of breeding and being proven?

Now if someone is selling homozygous spiders and they turn out not to be such I could see that being a problem but just coming out and saying “I think I have a homozygous spider, I’ll report back how the breeding results go” isn’t exactly going out on a limb. I’m thinking there has to be some other reason even if it is just that 7 years isn’t long enough with all the interest in outbreeding spiders.

I really no longer think that ball pythons that are homozygous for the spider allele show embryonic lethality.

Why?

Not because there are not examples of pleiotropy in ball pythons or reptiles…..the superwoma (the pearl) demonstrate that genes influencing bp skin color can influence other body systems.

Not because there are no examples of homozygous lethal alleles in any snake species. The Jaguar gene in Carpet pythons appears to be homozygous lethal. “Supers” die shortly after birth. See http://www.naturalselectionreptiles....hersnakes.html and http://www.jaguarpython.com/docs/jaghist.htm.

Even before I knew of the examples above, neither of these counterarguments to the homozygous lethal hypothesis for Spiders held much weight for me. Why? Cause they never disproved the idea of homozygous lethal. It always remained a possibility for me.

But let’s look directly at the predictions of the homozygous lethal hypothesis for Spiders.

Good hypotheses and predictions are based off sound prior knowledge. In this case biological knowledge of the reproductive biology of Python regius.

The following prediction follows logically from the homozygous lethal hypothesis for spider ball pythons and prior biological knowledge.


Prediction: If the homozygous spider genotype (SS) is lethal, then we would expect ~25% chance of slugging in Spider x Spider crosses.


How did I arrive at this prediction? First, we expect ~25% chance of the homozygous genotype from a Spider (Ss) x Spider (Ss) crossing.

Second, let’s look at what would happen to those approximately 1 in 4 chance homozygous spiders if they were embryonic lethals.

In ball pythons, fertilization occurs after ovulation in the infundibulum, an anterior portion of the oviduct .

“Prior to ovulation the growth of the follicles can be reversed and the follicles can be reabsorbed by the ovary. After ovulation there is no mechanism in the body to reabsorb the eggs—once the follicles are ovulated, in one shape or another, something is going to be laid.” See the following link off of kingsnake for more info and the quote. Also special thanks to our own Infundibulum Inspector (xdeus).

So if the homozygous lethal story stands up we would expect that those homozygote that failed to develop due to their genotype would produce nonviable eggs (slugs).

As far as I know there is no known higher rate of slugging from Spider x Spider crosses. If there is no higher rate of slugging, then it seems to me that we must reject the homozygous lethal hypothesis of spiders. If I am wrong or ignorant of some fact, please let me know.

SO what is going on with spiders? Hard to say…..these things take time to work out.

One idea is that perhaps there are homozygous spider adults, but perhaps they are the spiders that fail to reproduce. It could be that the homozygous spiders (SS) don’t have what it takes to produce good eggs and/or sperm. Are such pesky, dud parents more frequent to anyone’s knowledge in spiders?

Thanks!

So what is the definition of homozygous lethal? It was once suggested to me that the definition could be as broad as not being capable of reproducing. Does the woma/pearl qualify? Maybe there is a better term as the "lethal" part certainly seems to imply death and not just not being capable of it's biological imperative.

I do believe that at one point there was a post by someone in a large spider breeding camp that the spider X spider clutches didn't tend to slug any more than other ball pythons. I don't think any actual numbers or sample size was given. I still wouldn't rule it out as even normal ball pythons have been known to slug at rates that could compare to a homozygous lethal situation. But if you look at published large samples of non spider X non spider breedings like on Ralph Davis' breeding records pages it does seem the "normal" rate of slugs could be misleading as it's more often an all or nothing thing (some clutches totally bad but many others totally good rather than a steady high slug rate in all clutches). But I still question if homozygous spider eggs didn't hatch if it would be dismissed as a normal slug rate. It would take a pretty good sample size of spider X spider breedings and careful records to "prove" a trend if homozygous spider eggs don't hatch.

I also wonder if the homozygous spiders did hatch but where less perfect in some way like the pearl if we would hear about it. The pearl was the first reported cb white ball python so was very exciting to the community but unfortunately the lesson learned may have been to be much less forthcoming with information about any potential problems. If there are a couple similar projects now they might be sold for years before the details are publicly disclosed.

From Cornell University Dept. of Animal Science:

embryonic lethal genotype: Genotype whose expression results in the prenatal death of the individual possessing it.

lethal genotype: Genotype whose expression results in the death of the individual possessing it.

Note lethal alleles or genotypes just cause a premature death. That death does not need to occur during embryonic development or childhood. Huntington disease typically causes a slow and sad decline to death in middle age. You only need one copy of this allele to get the diease. Hence, its classified as a autosomal dominant disorder.