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The Cultivars (morphs)/Genetics Issues Discussions about genetics issues and/or the various cultivars for cornsnakes commercially available.

Genetics/Morph FAQ
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Old 12-28-2005, 04:51 AM   #1
Genetics/Morph FAQ


Q: What is a gene?
A: A hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism.

Q: What is a locus?
A: The position that a given gene occupies on a chromosome.

Q: What is an allele?
A: Any of the alternative forms of a gene that may occur at a given locus.

Q: What is meant by a characteristic?
A: A characteristic is anything in the phenotype that differs from the wild type phenotype.

Q: What does the term 'homozygous' mean?
A: Having the same alleles at a particular gene locus on homologous chromosomes.

Q: What does the term 'heterozygous' (het.) mean?
A: Having different alleles at one or more corresponding chromosomal loci.

Q: What is meant by a gene being dominant?
A: A gene that is expressed phenotypically in heterozygous or homozygous individuals.

Q: What is meant by a gene being recessive?
A: A gene that is phenotypically expressed in the homozygous state but has its expression masked in the presence of a dominant gene.

Q: What is meant by a gene being codominant?
A: Genes that are on a given loci that are both expressed in some degree.

*- The definitions of dominant, recessive and codominant imply a comparison to the wild-type. If one says that some gene is dominant without specifying to which gene, it is assumed that it is dominant to the wild-type.

Q: What is the 'wild-type'?
A: The wild type phenotype is the most common phenotype found in the wild population. The wild type allele is the allele at each locus that is required to produce the wild type phenotype. There are thousands of loci in the corn snake genome, and there is a wild type allele at each locus. If a gene is not expressly identified, it is assumed to be wild type.

Q: What does the term 'genotype' mean?
A: The combination of alleles located on homologous chromosomes that determines a specific characteristic or trait.

Q: What does the term 'phenotype' mean?
A: The observable physical characteristics of an organism, as determined by it's genetic makeup.

Q: What is a Punnett Square?
A: A type of grid used to show the gametes of each parent and their possible offspring; a type of grid that can indicate all the possible outcomes of a genetic cross.

Q: What is a morph?
A: One of various distinct forms of an organism or species.

Q: What is a cultivar?
A: A variety of a plant or animal that has been created or selected intentionally and maintained through cultivation.


Q: Can I tell the genotype of my snake just by looking at it?
A: Technically, no. For the most part it is impossible to tell if a snake is heterozygous for any given trait without doing breeding trials.

Q: What morphs are co-dominant?
A: The (DD) diffusion gene is (variably) codominant to (D+) it's wild-type counterpart. The (aa) amel and (au) ultra genes are codominant to each other, and both are recessive to (A+) their wild-type counterpart.

Q: What does 50% het or 66% het mean?
A: Both percentages reflect the statistical probabilty that each egg, not the clutch as a whole, will be some genotype xyz. If you breed two snakes that are both normals het amel together, the resulting statistical probabilty will be as follows: 1/4 amels, 1/4 normal, 1/2 normal het amel. Disregard the amels as they are showing the trait and cannot be het for it, and you are left with all normals, some het for amel and some not. Theoretically 1/2 out of 3/4 of the normals will be het for amel. 0.5 / 0.75 = 0.66667%.
The same holds true regarding 50% het. A normal x normal het amel will give all normal offspring, 50% being het for amelanism.

Q: What is an ultramel?
A: An ultramel has one amel gene, and one ultra gene. Since the genes both occur at the 'amel locus' and are co-dominant to each other, the resulting animal is one that looks something between an amel, and a hypo. Since this is a new morph, expect a lot of variation, especially due to the co-dominance. Ultramels can be made by crossing an ultra x amel = 100% ultramels, or by crossing ultramel x ultramel, ultramel x amel, or ultramel x ultra.

Q: How do I use a Punnett square?
A: A Punnett square is used to determine the possible outcomes of a cross. Links on how to do Punnett square crosses are found here:

Note: Mick's Cornsnake Progeny predictor is a great way of calculating possible outcomes AFTER you have learned how to do it by hand, and fully understand the way it works. Simply clicking on boxes and hitting calculate will not help you truly understand why you get 50% caramels from a caramel x normal het caramal pairing. The program can be found here:

*Pictures of most morphs can be found at, South Mountain Reptile's (SMR) website,,, and

Single recessive- Amelanistic, Anerythristic, Charcoal, Hypomelanistic A, Sunkissed, Lava , Ultra, Caramel, Bloodred*, Lavender, Motley, Aztec/Zigzag*, Stripe.

Double recessive- Butter, Amber, Snow, Ghost, Pewter, Granite, Blizzard, Ice.

Triple Recessive- Most triple recessives are double recessive morphs with a pattern mutation thrown into the mix. Pattern mutations are bloodred (diffused), Aztec/Zigzag, Motley, and Stripe. Some of these examples are butter motleys, snow motleys, butter stripes, etc.

Line-bred morphs- These are animals that are variations of certain genes.

Normal Type- Okeetee, Miami, Carolina.

Amelanistic- Sunglow (little or no white), Candy Cane (red or orange saddles with a clean white background), Reverse Okeetee (amel with thick white borders around the saddles).

Motley- Banded, Hurricane.

Snow- Coral (+Hypo), Bubblegum (high pink).

*- Bloodred is not truely a single recessive gene as it is co-dominant to it's wild-type. Aztec/Zigzag is also not a simple single recessive gene. Two snakes showing an aztec/zigzag pattern paired together do not always produce offspring that show that pattern. Likewise, snakes not showing the pattern sometimes have a tendency to produce offspring that do show that pattern. Both of these facts show that aztec/zigzag is not a true simple single recessive trait.

Special Note: As you might have noticed, I have decided not to use the terms Hypo B and Hypo C in correlation with Sunkissed and Lava, respectively. Sunkissed and Lava have been proven by breeding trials to be a different gene than the standard hypomelanism A, as has the newly found ultra. This means that if you were to breed any of these hypo-like traits together, you will get animals that are in fact normal, and not hypo at all. At this point in time, I am going to call the three additional traits hypo-like.

Genetic Makeup of Morphs

Amber: Caramel + Hypo
Blizzard: Charcoal + Amelanism
Butter: Caramel + Amelanism
Crimson: Miami + Hypo
Ghost: Anery A + Hypo
Granite: Bloodred + Anery A
Ice: Lava + Anery A
Opal: Lavender + Amelanism
Pastel: Anery A + Hypo (normally a very light ghost with pink hues).
Pewter: Charcoal + Bloodred
Phantom: Charcoal + Hypo
Snow: Amelanism + Anerythristic
Snow (Coral): Amelanism + Anerythristic + Hypo
Sulfur: Butter + Bloodred
Old 12-28-2005, 03:29 PM   #2

1. Move the definition of wild type above the definition of dominant.

2. Add the definition of "mutant gene" below the definition of "wild type".
Q. what is a 'mutant gene'?
A. A mutant gene is a gene with a DNA sequence that has been changed from the DNA sequence of the wild-type version of the gene. The changed DNA sequence often produces a change from the wild type phenotype.

3. Add this to end of the definition of wild type: "The standard against which a mutant gene is compared to determine whether the mutant is dominant, recessive, or codominant." This will allow deletion of the footnote below the definition of codominant.

4. Q: What is meant by a mutant gene being dominant?
A: A mutant gene that is expressed phenotypically in both heterozygous and homozygous individuals. The phenotype is the same in heterozygous and homozygous individuals.

Q: What is meant by a mutant gene being recessive?
A: A mutant gene that is phenotypically expressed only when in the homozygous state. When paired with a wild-type gene, the phenotype is the same as the wild-type phenotype.

Q: What is meant by a mutant gene being codominant?
A: A mutant gene that is expressed phenotypically in both heterozygous and homozygous individuals. The phenotype is not the same in heterozygous and homozygous individuals because both genes are expressed in some degree in heterozygous individuals. The phenotype may be intermediate between the two homozygous phenotypes, or sensitive tests may detect each gene's product. 'Codominant' has many synonyms, such as incomplete dominant, partial dominant, semidominant, transdominant, less than dominant, and others.

5. Move genotype and phenotype to follow the definition of gene. At present, 'phenotype' is used in the fourth definition.

6. Q. What are 'homologous chromosomes'?

A. Chromosomes that have the same linear sequence of gene loci. The gene at each locus on one of the chromosomes is either the same as or very slightly different from the gene at the same locus on the other chromosome. The corn snake has 18 pairs of homologous chromosomes, making a total of 36 chromosomes.

7. Q. What is a 'trait'?

A. A characteristic.

8. Change 'co-dominant' to the standard spelling -- codominant.

9. Add to definition of 'homozygous' -- The genes may be either two copies of the normal allele or two copies of a mutant allele.

10. Add to the definition of 'heterozygous' -- The genes may be a normal allele and a mutant allele, or they may be different mutant alleles.

11. Applications, Q 1 -- The genotype of an amelanistic corn is pretty obvious. The answer would be correct if "Can I tell" in the question is changed to "Can I always tell". And 'trait' should be changed to 'mutant gene'. A trait is a difference from the wild type phenotype, not a mutant gene.

12. Applications, Q 2 -- Put the superscripts back in the gene symbols.

13. Applications, Q 3 -- This is the probability that a given hatchling would be a particular genotype, not a given egg. The answer needs some work, in my opinion. I figure that, as 3/4 of all the babies from the cross are expected to be normal, then 1/2 of 3/4 of the normals would be 9/32 of all the babies.

14. Applications, Q 4 -- I think the answer needs some work.

15 Morph section: delete the normal type or change it to something like 'a snake that would not look out of place in most of the corn snake's range in the wild.'
Line-bred morphs -- These have been selected to either develop a certain look or retain a certain look that is found in the wild. For the most part, the genes responsible have not been identified. Examples include Okeetee, Miami, and blood red.

16. Kudos for using sunkissed and lava instead of hypo B and hypo C!

I'm out of time and must close.
Old 12-28-2005, 05:51 PM   #3
Just to let everyone know, while I do appreciate the input, this thread was up in the FAQ development forum for almost 7 months. Things were added and changed when suggestions were given. This is still not the final editing of the FAQ, but this really is not the place for suggestions.

Anyway, I've asked Rich to sticky this at the top, as well as the other 2 FAQ's, and to delete all subsequent posts on all the FAQ's.

More specifically, while I understand the point in your suggestions, this is not a genetics textbook and only is a basic explanation of cornsnake genetics. I do not want to get into long, textbook type answers as that for most people is quite confusing. If people want a more in depth understand of genetics they can either read Chuck's book or buy a genetics textbook. I think most of the answers are more than adequate for the purpose.
Old 10-29-2006, 08:50 AM   #4
You did a great job Joe!
Old 10-29-2006, 09:06 AM   #5
Joe, thanks for taking the time and effort to explain what these terms mean and the rest!

paulh, I don't know what to say, I thought that was rude of you towards Joe. A pm would have been more appropriate.
Old 07-13-2010, 02:40 AM   #6
do morphs last longer/shorter at all then classics?
Old 07-13-2010, 06:50 AM   #7
Originally Posted by ChiiCorn View Post
do morphs last longer/shorter at all then classics?
As far as I know, there is no difference in the lifespan from one morph to another or with the classics.
Old 07-13-2010, 02:34 PM   #8
ok sweet thanks...
Old 09-13-2011, 12:53 PM   #9
Nobody listed Axanthic?
Old 09-13-2011, 08:28 PM   #10
Originally Posted by BR289 View Post
Nobody listed Axanthic?
The list in the original post is 6 years old and needs to be updated. Not only that, but to date, no one has isolated/identified a gene that truly removes all yellow in corn snakes. Of course, that also depends upon your definition of axanthic as some sources also include red being removed, but we use anerythristic for that. I really suspect that cinder has an axanthic effect as I have yet to see any homozygous cinder with yellow. They have black and red pigment but if you look at the buttermints, they really don't have the expected yellow and what color they show reminds me of the more of the off-white color of an amel's saddle bands.

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