🧬 Genetics Reference
Reptile & Bird Breeding Glossary
Simple, accurate explanations of the most important genetics terms used by keepers and breeders of ball pythons, corn snakes, parrots, finches, and other exotic pets.
Recessive Needs 2 copies
A gene that is "shy" — it only shows its visual effect when a baby gets two copies (one from mom, one from dad). If a baby gets only one copy, it looks completely normal but can still pass the gene on. This is called being "het."
🐍 Reptile example: Albino ball python — you need two albino genes to see the bright white and yellow snake.
🦜 Bird example: Lutino cockatiel or ino budgie — needs two copies to produce the bright yellow or white bird.
Dominant 1 copy enough
A gene that is "strong" — only one copy is enough to show the visual effect. Even if the other gene is completely normal, the dominant trait still appears in the animal.
🐍 Reptile example: Woma ball python — one copy makes the snake visually different from a normal.
🦜 Bird example: Dominant Pied or Yellowface in budgerigars.
Co-Dominant 1 or 2 copies
One copy gives a visible change, and two copies create a stronger "Super" version. Very common in reptile breeding — the most versatile gene type for producing a wide range of offspring.
🐍 Reptile example: Pastel ball python — one copy gives soft pastel colors; two copies = "Super Pastel" (much brighter and more extreme).
🦜 Bird example: Opaline or Cinnamon mutations in certain parrot species.
Incomplete Dominant Blend of both
Produces a result that is somewhere between the two parents — a blend rather than one or the other. Many hobbyists use "co-dominant" and "incomplete dominant" interchangeably, though they are technically different.
🐍 Reptile example: Some line-bred hypo or strawberry corn snakes show blended expression.
🦜 Bird example: Many color mutations in lovebirds and finches where the result is a soft mix of parent colors.
Super 2 copies of co-dom
The enhanced version of a co-dominant gene — it happens when a baby inherits two copies of the same co-dominant gene. Super animals usually look more dramatic and are often more valuable. Not all Super forms are safe — some are lethal.
🐍 Reptile example: Super Pastel, Super Mojave, Super Enchi ball pythons — brighter, more extreme, and highly sought after.
🦜 Bird example: "Double factor" mutations in some parrot species.
Fatal Combination / Lethal Super ⚠ Avoid
Some Super forms are harmful or deadly. When two copies of certain genes are combined, the resulting animals have serious health defects or do not survive. Responsible breeders never intentionally create these pairings.
🐍 Reptile example: Super Spider ball python — these babies typically die in the egg or are born with severe neurological defects.
🦜 Bird example: Certain lethal double-factor mutations in budgies and finches — responsible breeders track and avoid these.
Het (Heterozygous) Carrier
Short for "heterozygous." The animal carries a recessive gene but does not show it visually — it looks completely normal. You can only confirm het status through its parentage or test breeding. A het animal will pass the gene on 50% of the time.
🐍 Common phrase: "Het Albino ball python" — looks totally normal but carries one copy of the albino gene and will pass it to roughly half its offspring.
🦜 Bird equivalent: "Split" — e.g. "split for Lutino" in cockatiels means the same thing as het.
Morph Reptile term
The term reptile keepers use for any color or pattern variation caused by genetics. It is the reptile equivalent of "color variety" or "mutation." Every distinct genetic color or pattern combination has its own morph name.
🐍 Examples: Albino morph, Piebald morph, Pastel morph, Clown morph — each describes a specific genetic makeup and visual appearance.
Mutation Bird term
The word bird keepers use instead of "morph." It refers to a natural or selectively bred change in DNA that produces a new color or pattern. In birds you will always hear "mutation" — rarely "morph."
🦜 Examples: Lutino mutation, Blue mutation, Cinnamon mutation, Pied mutation — each describes a specific gene change and visual result in the bird.
Polygenic Line bred
Traits controlled by multiple genes working together rather than a single gene. These traits improve gradually over many generations of selective breeding — you cannot produce the trait from a single pairing. Common in selectively bred color lines.
🐍 Reptile example: Blood Red corn snakes or extreme red ball python lines — bred over many generations for deep color intensity.
🦜 Bird example: Heavily selected show-quality budgies or exhibition cockatiels bred for size and feather quality.
Line Bred Selective breeding
Animals selectively bred within a specific breeder's program over many generations to enhance or intensify a trait. Line-bred animals often carry the breeder's name and may look noticeably different from standard versions of the same morph or mutation.
🐍 Example: "VPI Axanthic" ball pythons — a specific Axanthic line developed by Bob Clark at VPI that holds its gray color better than other lines.
🦜 Example: Specific show lines of English budgies bred for size and feather quality over decades.