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Genetics
First, just want to provide some basics here to help define some of the genetic terminology that is applied when selling garter snakes. Second, will provide some examples of Punnett squares used to predict the results of a particular cross. Third, will cover some material about pigmentation and how that relates to some of the known garter snake morphs.
Genetic terms- So what the heck is a garter snake morph? The term morph means: form, and as applied to animal breeding simply refers to an animal that has a different form than the wild type or normal, naturally occurring form of that animal. Usually this is in reference to a different color or pattern in terms of snakes. So, a garter snake morph is simply a garter snake that looks different than the normal, naturally occurring, wild type. The term morph does not specifically refer to an inheritable trait, but generally in the snake world it is not really considered a "genetic" morph until it is "proven" genetic. That is to say, that it has been proven thru subsequent breeding trials to be a genetically inheritable trait, i.e. the gene or genes for that differing appearance can be passed down from generation to generation. However it is fundamental to realize that a gene can be passed on and not be visually seen (or hidden) i.e. an animal that is heterozygous (defined in the next paragraph) for a simple recessive trait like albino.
When referring to a specified "gene" it is important to first realize that essentially an individual snake will have two copies of that specific gene, or more formally called a pair of alleles. An allele is defined as one of the different forms of a gene that can exist at a single locus (a locus is simply a specific place on a chromosome where a gene is located). So for each pair of alleles of a gene within an individual snake; one came from its maternal parent (Mom) and one came from its paternal parent (Dad). Examples: If a snake received one copy of the albino gene from its mother and one copy of the albino gene from its father, it will have a pair of albino alleles at that gene locus, and is said to be "homozygous" for albino, since the alleles are the same. Since albino is a usually a simple recessive trait and would thus require two copies to display the albino phenotype (the definition of phenotype is: the form that is shown) so this snake will be an albino. If however the snake received only one copy of albino from one parent and one copy of the wild type allele at the albino gene locus, then that snake would be said to be "heterozygous" (two different alleles at the given locus) and in the case of a recessive gene this animal would display the wild type phenotype (look normal) however it would be carrying one copy of the albino gene that could be passed on to subsequent generation.
Many, if not most, garter snake morph genes are recessive traits, however there are a few dominant gene morphs, and a few that are termed dominant that arguable might be better defined as polygenic traits with variable dominance (this topic will be discussed later in this page). In the case of a dominant trait only one copy of the mutant form of the gene is required to produce the phenotypical animal i.e. if a snake receives one copy of axanthic plains gene from one of the parents and one copy of the wild type allele for that gene locus; the snake would still be phenotypically axanthic (having axanthic appearance).
Example morphs such as "flame" and erythristic may be termed as dominant or recessive depending on which way the resulting offspring ratio leans toward from the breeding (cross) of the original parent to a wild type and subsequent back crosses, yet there is usually a wide range of the phenotype and relative amount of the morphs "looks" that are produced, or "show thru". While those classifications of dominant or recessive are not necessarily right or wrong, I would like to suggest that perhaps a better definition would be; they are likely polygenetic traits (meaning that there several or many different genes or multiple alleles involved, rather than a single point gene mutation as in the case of a simple recessive or dominant trait that results in an "on" or "off" phenotype) and results in variable amounts of dominance or incomplete dominance in subsequent generations depending on the variable amount of inheritance of the group of genes, or the variable amount of effect that is displayed. It is likely that subsequent breedings of out crossing to the wild type would after a few generations result in the diluting of the morph genes to effectively zero, as opposed to a simple recessive gene the animal has it or they don't, which can be proven. So a "het." may not really a het. by strict definition. This can be validated in the example of Dr.Phil Blais's selective line breeding of the flames, just as the amount of red can be increased thru selective line breedings, it will be diluted thru outcrossings. This is important to keep in mind when predicting the resulting offspring from multiple morph combos utilizing these types of morphs and realizing that there will be variability.
It is very important to note that after having said all this, that having discussed this topic with numerous snake breeding authorities, the reality is that a term is just a term, and we use them to define things, so it doesn't matter how technically correct or specific you define or term something if nobody knows or cares what it means, it has no value then. The bottom line is that there is a lot that we simply "really" don't know about, and how some of these genes exhibit their effect or what effect they will have in combination with other morph genes. To me, that is part of the excitement in breeding; the element of surprise. To really know exactly what is happening you would need to identify what the changes or mutations are at a genetic sequence level, and also how and what effects that is having on proteins, protein synthesis, and altering of a biochemical pathway, or if a protein is just changed, or deleted, or altered regulation of its manufacture, ect. ect. These are some of the specifics that are being mapped out in the human model, but it's doubtful that anyone is forking out the money to do those studies on garter snakes, but maybe someday? Maybe someday creating designer morphs won't just be breeding snake morphs but will be artificially manipulating genetic material to create a purple garter snake with florescent green spots that glows in the dark (wouldn't that be wild looking at night) and then cloning it. So for simplicity sake I will generally stick with the general standard use of recessive or dominant to define garter snake morphs for now. I only introduce these suggestions as food for thought for the readers to start thinking a little bit "outside the box" of simple "Mendelian genetics 101."
It gets really fun when you start crossing the different morphs, creating new combinations of multiple morph traits to create new "designer" morphs. An example of this would be the "snow" which is a snake that is homozygous for both albino and anerythristic, the result is a snake that has pink eyes and has very little to no pigment or pattern, some of these basic "how and what" principles and results will be discussed later in the pigment section. Snake breeding in general has really probably only "scratched the surface" or found the "tip of the iceberg" with regards to the endless possibilities of creating designer morphs. This idea of the future possibilities really gets me "fired up" and excited about breeding and I hope it does you too!!!
Punnet Squares- Let's look at some examples of Punnet squares. The Punnett square is used in snake breeding to predict the types, frequency, and ratio or percentage of the resulting offspring resulting from a particular breeding cross. This is done by putting the gamete possibilities (the definition of a gamete in simple terms as it is used here is a sex cell either sperm or egg which contains 1/2 the genetic material as the fertilized or adult cells) of one parent across the top of the square horizontally, and then putting the gamete possibilities of the other parent up and down the sided of the square vertically.
For example let say we breed a snake that is 100% het. for albino with another snake that is the same. We will use (A) for the wild type allele at the albino locus and (a) for the albino allele at the same locus.
A snake that is het for albino has the genotype Aa , but is the phenotype normal wild type because the albino allele is recessive to the wild type allele.
So the parent could produce a gamete that is either A or a, those are the only 2 possibilities. Hence the punnet square would look like this.
Where the gametes are in the gray boxes and the genotypes of the resulting offspring would be in the tan boxes. So of the offspring there is 1 AA, 2Aa, and 1 aa, were 1AA would be wild type, the 2 Aa would be het. for albino, and the aa would be albino. The AA and the Aa would both be phenotypically wild type and so you would not be able to tell them apart so 2 of the 3 (so if you take 2/3 =.66 and multiply by 100 for % = 66%) would actually be het albinos, since you cannot tell them apart they would thus all 3 would be listed as 66% possible het for albino. So for example in a litter of say 24 babies you would statistically on average produce 6 albinos (25%) and the other 18 (remaining 75%) babies would be normal looking but they would have a 66% chance of being het. for albino. Real litters can vary some from those numbers.
It is also fundamental to realize that if a snake is said to be 66% het., it is in reality either heterozygous or not, which can be proven by subsequently breeding that snake. Either it carries a copy of the gene and can produce albinos, or it does not and can not. The 66% is referring to the CHANCE that it has one copy of the gene, not that it has 66% of the gene or will pass it on 66% of the time. I hope this makes sense because it can be a common misconception and understanding this concept will save any disapointment if a possible het. does not prove out.
Let's do another punnet square-this time with a snake that has 2 different genes. You can do a punnet square for any number of genes, the table just gets taller and/or wider to accommodate the number of gamete possibilities.
In this example let's use a snow as the father and a double het. for anerythristic and albino as the mother. The reason I chose this example is to show that a punnet square does not always have to be a true square, it can be more of a rectangle, because the shape is dependant only on the gamete possibilities of the parents. So if the father is a snow, he is homozygous for both albino and anerythristic so we will use aa for albino and we will use blue aa for anerythristic. So the genotype of the father is aaaa, and the mother is AaAa. The father has the gamete possibilities of aa only and the mothers gamete possibilities are AA,Aa,aA,aa. So putting the father's gamete on the side and the mother's gametes on the top the punnet square would look like this.
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AA |
Aa |
aA |
aa |
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aa |
AaAa |
Aaaa |
aaAa |
aaaa |
As you can see this would be a very productive cross to do because it would yield as are right to left in the tan boxes, approx. 25% double hets, 25% anerythristics, 25% albinos, and 25% snows.
I hope that these punnet square examples help to demonstrate how and why you sometimes see 66% hets as well as how to predict the possible outcomes and expected approximate ratios of any breeding cross. There are many sources in books and on the web with many more examples and in depth genetic studies that you can learn from but that is way beyond the scope and what I want to cover on this page.
Pigmentation-Let's look at a few of the known basic aspects of pigmentation and the how and what causes these morphs to look the way they do. Let's start be defining a few terms first. Chromatophores-these are cells that contain pigments and also may have some degree of reflecting qualities. With in the group of choromatophores there are melanophores (which contain black and brown producing pigments such as melanin), xanthophores (containing yellow producing pigments such as xanthin), erythrophores (red producing pigments-erythrin), iridophors (producing reflective iridescent structural color), leucophores (white) and cyanophores (blue).
To my knowledge, I don't know if it has been proven or dissproven that garters produce cyanophores, it rare and know in a few fish, so would not be likely to be in garters, but not impossible.
It is just as likely, actually probably more likely that the blues on say Pugets or Axanthix Plains or Similis, are the result of a different mix, ratio, or blending and layering of the typical pigments Zanthin, Erythrin, and Melanin in combination with structural light reflective and refractive qualities of Iridophores, resulting in blue light bouncing back into our eyeball. These are my oppinions/theory based on my biochemistry educational background, but I have not done any research, nor read any official publications specifically addressing specific pigments found in blue garter snakes, so take it with a "grain of salt" The way the pigments work is that they change what colors or wavelengths of white light are reflected back to our eye by selectively absorbing other colors or wavelengths. Iridescence of some snake's skin, especially in certain lighting or angles, is more the result of structural color, which is the result of selective reflection and refraction.
Sometimes the removal of pigment colors, as is the case with the Iowa snow plains morph, results in more pronounced reflective iridescent structural colors and more white remaining. In addition some pink tones and if you look at the skin of an Iowa snow with a magnifying glass you can see tiny pink blood vessels showing due to a lack of pigment proteins covering them. A good example of structural color is seen in the increase in the iridescence on the belly of a melanistic garter when they are in "blue", the milky fluid separating the old skin from the new blocks out some of the pigment underneath in the new skin, which produces a beautiful iridescent blue belly that is otherwise satin jet black, and anyone who has raised a melanistic eastern knows exactly what I am talking about.
Anerythristic is a genetic mutation that causes the lack of erythrin resulting in a color dull snake of blacks and grays, sometimes blueish or greenish gray, which actually make for a beautiful snake even though it lacks the bright reds, oranges and yellows. The terms anerythristic and axanthic with their respective applications and usage, can be a bit confusing to say the least, especially if you look at their usage within multiple different snake groups. Keep in mind that these terms are merely an attempt to distiguish and describe the visual phenotype, and is often simply a guess a what is occuring on the biochemical pigment level. Often times what determines weather a morph is called anerythristic versus axanthic is relative to what has changed in the morph when compared to the base or wild type colors. Some examples of anerythristics and axanthics also appear to also have an increase in black color or melanin, and could arguable be called melanistic as well, such is the case with the anerythristic plains garter.
The anerythristic plains garter is a jet black snake with black eyes, yet it still retains its checkering pattern and is not a solid black snake like the melanistic eastern.
Melanistic is the result of overproduction of melanin, resulting in a predominantly solid black snake usually with black eyes as well, although not necessarily a truely solid black snake, as the melanistic easterns usually have a bit of white on the chin. The melanistic eastern appears to be a pattern mutation as well, because it is a solid black patternless snake, except for the small patches of white under the chin. Interestingly, when the melanistic eastern is combined with the Schuet albino gene the result is a snow looking snake that has the solid pattern (with the remnantsof the white chin patch) still slightly visible of the melanistic but has nearly all pigment stripped away, however it is not nearly as pigmentless as the Iowa plains snow, and the more recently produced snow red-sided appears to be the most completely pigmentless snow yet.
The "Silver" morph of the eastern garter appears to not only have a major loss of xanthin and eurythrin, but also a minor loss of melanin as well so it's really hard to put it in a typical descriptive pigment class mutation, it has a similar appearance to the Lavender morph in corn snakes. I am really excited about working with this new morph and future combinations.
The Axanthic plains is a dark snake with blue sides and a greenish dorsal stripe. This gene is what appears to be the only known truely dominant gene in the garter snake morph world. Thus far it appears to have a dominant or masking effect over the albino gene as well, although is also looks like it may be a codominant allele to anerythristic at the same loci. More breeding trials are needed and will be done in the next couple years to further and more specifically characterize the axanthic plains gene. An axanthic chicago garter morph also exists and I look forward to working with this gene as well. There is a lot of work to be done to further characterize this gene and its interaction with other morph genes.
Erythristic is the result of overproduction of erythrin and the result is a spectacular increased red snake, examples are shown in easterns and plains although it does not look like a simple recessive at this time. additionally you could make the argument that the flame morph is a form of erythristic.
Albinos generally have a complete lack of melanin, yet still can produce xanthin and erythrin, which is why they will still have varying amounts of reds, yellows, and orange. That is why the combination of erythristic morph types with albino has enormous appeal and designer morph potential. The reptile world often classifies albinism into two main types of albinos: Tyrosinase positive (T+) and Tyrosinase negative (T-). Tyrosinase is an enzyme that is involved in one of the first steps to melanin production, it converts the amino acid tyrosine into the compound dopaquinone. Ablino snakes are often lumped into one of the two groups T+ or T- based on the idea that the T+ albinos have a darker more caramel/purple look, however this is a guess at best and a gross oversimplification of what causes the different albinos in snakes, due to a lack of knowledge and research being done at the biochemical and genetic level of snakes, and/or public knowledge of such studies. Having many different possibilities or mechanisms that can cause albinism is the reason that even though two types of albinos in a species may or may not be genetically compatible, so when 2 albinos from different parentage are crossed might not produce albinos but rather double hets for the two different albino types. For example it is well know that the Iowa albino and Nebraska albino types in the plains garter are not compatible, and recently it was discovered that the Bluegrass albino and Shuett albino in the eastern garter are not compatible.
These are just some examples of the main, common types of color morphs, there are many more, and likely more to come in the future. Just recently there was also a bright yellow form of the checkered garter introduced as a hypo that is codominantly inherited. This snake appears to actually have an increase in yellow or xanthin, so could be considered a hyperxanthic, however this brigher color could also be the result of reduced overlay of blacks and browns from a melanin layer, which is why it has been named a hypo. Many people feel the term hypo is overused, and sometimes even misused to discribe a lighter variant individual thruought the entire reptile industry in general.
There are also different pattern mutation morphs like the more recently available; granite morph, which is a pattern mutation in the checkered garters that alters the uniform checkered pattern into a more finely randomized granite looking pattern, which certainly has some great future potential to cross with color morphs. Joe Peck produced 2 plains garters that have a lack of checkering and thus have a striped look, they have to be proven as a genetically inheritable trait, but look promising, and would be a great pattern mutation to add to new combo possibilities if it does prove out.
If there are any biologists, herpetologists, geneticists, or other breeders out there who stumble across this web page and have additions or insight, I would really love to hear from you. I will always be looking to make additions and improvements, and will be continually adding and amending.
Not claiming to know everything or be an expert, the real experts are the wildlife field scientists, biologist, and herpetologist who dedicate their lives and put in the hours and hours of research. Just trying to share some of what I do know about keeping and breeding of the garter snake morph with the readers and hopefully getting new people interested in and excited about the beautiful, intelligent and entertaining garter snake, that is both fun and interesting to breed as well. Hopefully some of the readers will find some value in this page.
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