Genes come in pairs. The two members of the pair are either the same or different. If the two are the same, either two normal genes or two identical mutant (changed from the normal) genes, then the creature is homozygous for that gene. If the creature has a normal gene paired with a mutant gene, then it is heterozygous for the mutant gene.

Note that the above definition refers only to the genes. There is no specification for the appearance of the heterozygous individual. The heterozygous individual's look determines whether a mutant gene is dominant, codominant, or recessive to the normal version of that gene.

If a heterozygous individual looks normal, then the mutant gene is recessive to the normal version.

If a heterozygous individual looks like the homozygous mutant individual, then the mutant gene is dominant to the normal version.

If a heterozygous individual does not look normal and does not look like the homozygous mutant individual, then the mutant gene is codominant to the normal version.

Those three are the ideal definitions. Nature is sloppy, so sometimes we have to make a judgment call.

Most mutant genes known in reptiles are recessive to the normal version of the gene. Some exceptions are tiger in the reticulated python (codominant), pastel in the ball python (codominant), and striped in the California king snake (dominant).

Hope this helps.

Paul Hollander

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