Boa genetics

Boa genetics in simple terms

Incomplete Dominant Genetics in Boa imperator

In boa constrictors, incomplete dominance is a genetic pattern where the heterozygous (one-copy) form of a trait produces a noticeable effect, while the homozygous (two-copy or “super”) form results in an even more extreme version of the trait. This means that:

• A boa with one copy of the gene (heterozygous) will show a modified pattern or coloration.

• A boa with two copies (homozygous or “super” form) will have an enhanced or exaggerated expression of the trait.

This is different from dominant genes, where just one copy is enough to fully express the trait, and recessive genes, which require two copies to be visible.

Breeding Outcomes with Incomplete Dominant Genes

When breeding a boa with an incomplete dominant trait to a normal boa (heterozygous x normal):

• 50% of the offspring inherit the trait (heterozygous form).

• 50% remain normal.

When breeding two boas with the same incomplete dominant trait (heterozygous x heterozygous):

• 25% will be normal (no copies of the gene).

• 50% will be heterozygous (showing the trait).

• 25% will be the super form (enhanced expression, or in some cases, non-viable).

Incomplete dominant genes create a visible change in heterozygous form.

• Super forms often have an exaggerated expression of the trait.
• Some super forms, like Super Motley, are non-viable.

These traits can be used to create stunning combinations with other morphs.

Recessive Genetics in Boa Constrictors

In Boa constrictors, recessive traits follow the basic principles of Mendelian genetics. These traits are only visible when an individual inherits two copies of the recessive gene—one from each parent. If a boa has only one copy, it is considered a heterozygous (het) carrier and will appear normal but can pass the trait to offspring.

How Recessive Genes Work

1.    Visual Recessive (Homozygous Recessive)

• A boa must inherit two copies of the recessive gene (one from each parent) to physically express the trait.
• Example: An Albino Boa (T- Albino) has two copies of the albino gene (aa) and lacks black pigment.

2.    Heterozygous (Het Carrier)

• A boa with only one copy of a recessive gene does not display the trait but can pass it on to offspring.
• Example: A het Albino boa (Aa) looks normal but carries the albino gene.

3.    Breeding Outcomes

• Visual × Visual (aa × aa) → 100% Visual offspring
• Visual × Het (aa × Aa) → 50% Visual, 50% Het
• Het × Het (Aa × Aa) → 25% Visual, 50% Het, 25% Normal (non-carrier)
• Het × Normal (Aa × AA) → 50% Het, 50% Normal
• Normal × Normal (AA × AA) → 100% Normal (no carriers)

Common Recessive Traits in Boa Constrictors

• Albino (T- Albino) → Lacks black pigment (e.g., Kahl Albino, Sharp Albino)

• Anery (Anerythristic) → Lacks red pigment (e.g., Type 1 Anery, Type 2 Anery)

• Blood → Enhances red pigmentation

Double and Triple Recessive Morphs

Some morphs require multiple recessive genes, making them more challenging to produce.

• Snow Boa = Albino (T-) + Anery (double recessive)

• Moonglow Boa = Albino + Anery + Hypo (double recessive + incomplete dominant)

• Paradigm Boa = Sharp Albino + Boa Woman Caramel Albino (T- + T+)

Because these require specific genetic combinations, careful breeding is necessary to produce them consistently.

Dominant Genes in Boa Constrictors

Dominant genes in Boa constrictors follow simple Mendelian genetics, meaning that if a boa inherits even one copy of the dominant gene from a parent, the trait will be visually expressed. Unlike recessive genes, dominant traits do not have “hets” because a heterozygous (single-copy) snake looks the same as a homozygous (double-copy) one.

Key Features of Dominant Genes

1.    Only one copy of the gene is needed for the trait to be visible.

2.    There is no “het” form (unlike recessive traits, where heterozygous boas appear normal).

3.    Breeding a dominant boa to a normal one results in 50% dominant offspring.

4.    Homozygous dominant individuals (super form) often do not exist or are visually identical to heterozygous forms.

Examples of Dominant Genes in Boa Constrictors

1. IMG (Increasing Melanin Gene)

   o   One of the most famous dominant genes in boas.

   o   Boas with this gene start out lighter and darken over time with each shed.

   o   The name “IMG” (Increasing Melanin Gene) was coined by Pete Kahl.

   o   When combined with other morphs (like Anery or Motley), it produces extremely dark or nearly black boas

2. Inca

   o   A pattern mutation that creates chaotic, interconnected saddle markings.

   o   Originally discovered in Colombian boas. Vin Russo bred the first ones and introduced them to the hobby.

   o   Works well when mixed with color mutations like Albino and Hypo.

3. Indy

   o   A lesser-known dominant morph.

   o   Not much information is available, but it alters both pattern and color.