Genetics
Originally written by Joe Cala.
Republished, Updated & Edited by Stephanie Kunder.
Glossary
Allele - Any of the alternative forms of a gene that may occur at a given locus.
Co-Dominant - Relationship between two alleles where both are expressed equally when heterozygous to each other, resulting in three phenotypes. Red + White = Equal Parts Red & White
Cultivator - A variety of a plant or animal that has been created or selected intentionally and maintained through cultivation.
Dominant - A gene that is expressed phenotypically in its heterozygous and homozygous forms.
Gene - 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.
Genotype - The alleles present at a give locus.
Heterozygous - Unalike alleles at a given locus.
Homozygous - Alike alleles at a given locus.
Hybrid - Cross between two different species or geneses in captivity.
Incomplete Dominant - Relationship between two alleles where both are expressed in a blending when heterozygous to each other, resulting in three phenotypes. Red + White = Pink
Intergrade - Cross between two different species or subspecies that can be found naturally in the wild.
Locus - The position that a given gene occupies on a chromosome.
Mendelian - A trait (morph) that follows certain expression patterns because of a pair of alleles inherited from each of its parents.
Phenotype - The observable physical characteristics of an organism, as determined by it’s genetic makeup.
Recessive - A gene that is phenotypically expressed in the homozygous state but has its expression masked in the presence of a dominant gene.
Selective Breeding - Breeding program which has a goal of reproducing or enhancing a particular look found in the parents.
* 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.
Question & Answer
Q: What is meant by a characteristic?
A: A characteristic is anything in the phenotype that differs from the wild type phenotype.
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 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: Can I tell the genotype of my snake just by looking at it?
A: For the most part it is impossible to tell if a snake is heterozygous for any given trait without doing breeding trials. At times their are cases such as with Caramel, Diffuse and Sunkissed where hets can be picked out from non-hets in a clutch based on how they look. This is in no way fool proof and should not be used as a method to accurately identify hets.
Q: What does 50% het or 66% het mean?
A: Both percentages reflect the statistical probability 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 probability 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.
