Boa constrictor morph genetics (the basics)
note: These basics apply to all animal genetics.
Terminology
allele: One alternative, or variant, version of a gene that determines phenotype.
dominant trait: A trait that is dominant over wild-type. Motley, jungle, hypo, etc. are dominant traits in boas. The phenotype is expressed when the genotype is heterozygous (one dominant gene and one wild-type) and does need to be homozygous (as is the case for recessive traits).
gene: A basic unit of heredity (transferred from a parent) that occupies a specific location on a chromosome and determines a trait. Genes are inherited as one entity and alleles in a pair. Genes determine genotype.
Genes consist of two or more possible alleles. Each human carries two alleles (variants) of every gene. An organism with two gene variants for each gene is called a diploid organism.
heterozygous (het.): Two different alleles at a single locus.
Example: Heterozygous albino is Aa. This means the boa has one wild-type allele (A) and one albino allele (a).
homozygous (homo.): Two identical alleles at a single locus. Boas referred to as "supers" are homozygous for a dominant trait. A super hypo has two hypo alleles, for example, and will always pass the hypo trait to every offspring.
Example: Homozygous albino is aa. This means the boa has two albino alleles (a) and will always pass an albino allele to its offspring. Homozygous is most commonly used when referencing dominant traits, but homozygous also applies to recessive traits (or homozygous recessive) when discussing the genotype.
recessive trait: A trait that is recessive to wild-type. Albino, anerythrism, blood, etc. are recessive traits in boas. The phenotype is expressed only when the genotype is homozygous (two recessive genes).
wild-type: The typical form of an organism as it most frequently appears in nature (i.e. a normal boa). Wild-type boas have a normal phenotype and a normal genotype (unless carrying a recessive trait).
Abbreviations
anerythristic: anery
hypomelanistic: hypo (this trait is dominant in boas but recessive in other species)
double heterozygous (DH): Heterozygous for two traits. For example, a boa that is het. albino and het. Type I anery is DH snow.
triple heterozygous (TH): Heterozygous for three traits.
Genetics Basics
In genetics, the dominant gene is traditionally symbolized with a capital letter. The genotype of a heterozygous albino boa is displayed as Aa. This means one wild-type gene (A) and one albino gene (a) since wild-type is dominant over albino. A heterozygous (non-super) hypo boa is displayed as Hh. This symbolizes one hypo gene (H) and one wild type gene (h) since hypomelanism is dominant over wild-type.
The percentages in the examples below apply to all simple recessive, dominant, and co-dominant/incomplete dominant traits. You may substitute traits inherited in the same manner and use the same percentages below. For example, you can exchange albino with blood, or exchange hypo with motley.
Punnett Square
Genetic outcomes can be derived using a Punnett square. This example is a breeding between a het. albino (Aa) and a het. albino (Aa). Each parent has the same genotype (Aa). This means each parent has one wild type gene (A) and one albino gene (a). Each baby will receive one gene from each parent. The possible genotypes are shown in the example.
By breeding a heterozygous albino boa to another heterozygous albino boa, the litter should yield the following:
25% albino (aa)
50% het. albino (Aa)
25% wild type (AA)
The wild-type and heterozygous albino boas will all have the same wild-type phenotype, but they will have differing genotypes. Since they are indistinguishable in appearance, all wild-type phenotype boas from this breeding are referred to as "66% possible heterozygous albino" since 2 in every 3 (or 66.6%) of the wild-type boas should be heterozygous albino.
Example Genetic Outcomes
albino x motley
- 50% motley het. albino
- 50% het. albino
The first line (bold and underlined) details the genetics of the breeding pair. It does not matter which is female (dam) and which is male (sire).
The following lines (bulleted) show the scientific probability for the offspring. In this example, 50% of the babies should be motley het. albino. The other 50% should be wild type het. for albino. All offspring will be 100% het. for albino.
NOTES: You can substitute any recessive or dominant traits for those used below (i.e. substitute anery for albino, or motley for hypo). Any het. below will be a wild-type phenotype unless stated otherwise (i.e. het. albino = wild-type het. albino).
Outcomes
Albino breeding (or substitute any recessive trait)
albino x albino
- 100% albinos
anery x albino
- 100% het. albino and anery (DH snow): all wild-type phenotype but some het. anery boas are lighter/faded
hypo (het.) x albino
- 50% hypos het. albino (DH sunglow)
- 50% het. albino
Super hypo (homo.) x albino
- 100% hypo het. albino (DH sunglow)
wild type x albino
- 100% het. albino
Het. Albino breeding
albino x het. albino
- 50% albino
- 50% het. albino
het. albino x het. albino
- 25% albino
- 50% het. albino
- 25% wild type
anery x het. albino
- 50% het. anery and albino (DH snow)
- 50% het. anery
hypo (het.) x het. albino
- 25% hypos het. albino (DH sunglow)
- 25% hypos
- 25% het. albino
- 25% wild type
super hypo (homo.) x het. albino
- 50% hypo het. albino (DH sunglow)
- 50% het. albino
wild type x het. albino
- 50% wild type het. albino
- 50% wild type
Double Recessive Trait Breeding
het. albino and anery (DH snow) x het. albino and anery (DH snow)
- 6.25% snow
- 12.5% albino het. anery
- 12.5% anery het. albino
- 6.25% albino
- 6.25% anery
- 25% het. albino and anery (DH snow)
- 12.5% het. albino
- 12.5% het. anery
- 6.5% wild type
albino het. anery x het. albino and anery (DH snow)
- 12.5% snow
- 25% albino het. anery
- 12.5% anery het. albino
- 12.5% albino
- 25% het. albino and anery (DH snow)
- 12.5% het. albino
albino het. anery x albino het. anery
- 25% snow
- 50% albino het. anery
- 25% albino
albino het. anery x anery het. albino
- 25% snow
- 25% albino het. anery
- 25% anery het. albino
- 25% het. albino and anery (DH snow)
anery het. albino x het. albino and anery (DH snow)
- 12.5% snow
- 25% anery het. albino
- 12.5% albino het. anery
- 12.5% anery
- 25% het. albino and anery (DH snow)
- 12.5% het. anery
anery het. albino x anery het. albino
- 25% snow
- 50% anery het. albino
- 25% anery
snow (albino and anery) x het. albino and anery (DH snow)
- 25% snow
- 25% albino het. anery
- 25% anery het. albino
- 25% het. albino and anery (DH snow)
snow (albino and anery) x albino het. anery
- 50% snow
- 50% albino het. anery
snow (albino and anery) x anery het. albino
- 50% snow
- 50% anery het. albino
snow (albino and anery) x snow (albino and anery)
100% snow
Triple Heterozygous Recessive Trait Breeding
het. albino het. anery het. blood x het. albino het. anery het. blood
- 1.5625% albino anery blood
- 3.125% albino anery het. blood
- 1.5625% albino anery (snow)
- 3.125% albino blood het. anery
- 1.5625% albino blood
- 6.25% albino het. anery het. blood
- 3.125% albino het. anery
- 3.125% albino het. blood
- 1.5625% albino
- 3.125% anery blood het. albino
- 1.5625% anery blood
- 6.25% anery het. albino het. blood
- 3.125 % anery het. albino
- 3.125% anery het. blood
- 1.5625% anery
- 6.25% blood het. albino het. anery
- 3.125% blood het. albino
- 3.125% blood het. anery
- 1.5625% blood
- 6.25% het, albino het. anery (DH snow)
- 6.25% het. albino het. blood
- 6.25% het. anery het blood
- 3.125% het. albino
- 3.125% het. anery
- 3.125% het. blood
- 12.5% het. albino het. anery het. blood (TH)
- 1.5625% wild-type
Double dominant trait breeding
arabesque (het.) x motley (het.)
- 25% motley arabesque
- 25% motley
- 25% arabesque
- 25% wild type
arabesque (homo.) x motley (het.)
- 50% motley arabesque
- 50% arabesque
arabesque (het.) x motley (homo.)
- 50% motley arabesque
- 50% motley
arabesque (homo.) x motley (homo.)
- 100% motley arabesque
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