Genetics Basics for Breeders — Understanding the Fundamentals of Selective Breeding

Understanding basic genetics can deepen your enjoyment of medaka and reptile breeding. While it may sound complicated, learning the fundamental rules enables you to predict "what percentage chance there is of producing a target individual from a given pairing."

Mendel's Laws (Dominance and Recessiveness)

These are the fundamental laws of heredity discovered by 19th-century botanist Gregor Mendel.

The Concept of Dominant and Recessive

Organisms inherit one gene from each parent, possessing a pair of two genes (alleles).

• Dominant gene: Expressed as a trait (appearance, etc.) with just one copy
• Recessive gene: Only expressed when two copies are present (hidden with one copy)

Genetic Notation

Genes are represented with uppercase (dominant) and lowercase (recessive) letters.

• AA = Homozygous dominant (two copies of the dominant gene)
• Aa = Heterozygous (one dominant, one recessive copy) -- appears dominant in phenotype
• aa = Homozygous recessive (two copies of the recessive gene) -- recessive trait is expressed

Co-dominant Morphs (e.g., Ball Python Pastel)

Among reptile morphs (color and pattern variations), some are inherited in a "co-dominant" fashion---neither purely dominant nor recessive.

Co-dominance Characteristics: - Heterozygous (one copy): Intermediate appearance (slightly altered from the wild-type) - Homozygous (two copies): More pronounced appearance

Ball Python Pastel Example

• Normal: Standard coloration
• Pastel (heterozygous): Slightly brighter coloring
• Super Pastel (homozygous): Even brighter yellow

To produce the "super form," pastel-to-pastel breeding is required.

The Concept of Het (Heterozygous) and Homo (Homozygous)

Heterozygous (het)

An individual carrying one copy of a recessive gene that is not visibly expressed is called "het."

Example: The albino gene in ball pythons is recessive. An individual carrying one copy of the albino gene appears normal in phenotype. Such an individual is labeled "100% het albino."

Het individuals cannot be identified by appearance alone, making breeding records (parent information) crucial.

Homozygous (homo)

An individual carrying two copies of a recessive gene with the trait visually expressed. An albino individual is homozygous for the albino gene.

How to Read a Punnett Square

A Punnett square is a diagram for predicting breeding outcomes.

Example: Crossing Two Het Albinos

When both parents are "Aa" (A being the normal gene, a being the albino gene):

| | A (Parent 2) | a (Parent 2) | |---|---|---| | A (Parent 1) | AA | Aa | | a (Parent 1) | Aa | aa |

Results: - AA (Normal homozygous): 25% - Aa (Het albino): 50% - aa (Albino): 25%

This means "the probability of producing an albino from het-to-het pairing is 25%."

Risks of Inbreeding

Inbreeding (breeding between close relatives) is used to fix or emphasize specific genes, but it carries risks.

Benefits: - Can fix specific traits (color, pattern, shape) in a short period - Increases genetic purity

Risks: - Harmful recessive genes are more likely to be expressed (deformities, diseases) - Reduced immune function - Decreased reproductive capability - Inbreeding depression (individuals become weaker over generations)

Practical Advice

• Avoid more than 3 generations of inbreeding
• Periodically introduce individuals from different bloodlines for outcrossing
• Limit sibling matings to 1-2 generations

Find Quality Animals on BuriChoku

Understanding genetics changes how you select parent animals for breeding. Many breeders on BuriChoku clearly list genetic information (het status, etc.) in their listings, enabling you to make purchases based on confirmed genetic data. For those who want to enjoy targeting specific morphs and varieties through genetic combinations, BuriChoku is the ideal place to find reliable parent stock from trusted breeders.