GENETICS POST #wcrgenetics "A-LOCUS"
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TERMINOLOGY & DEFINITIONS
[ Heterozygous ] - refers to different inherited forms of a gene on one particular allele [ Homozygous ] - refers to identical inherited forms of a gene on one particular allele [ Dominant ] - a dominant gene is a particular variant of a gene, which for a variety of reasons, expresses itself more strongly all by itself than any other version of the gene on a particular allele. [ Recessive ] - a recessive gene is a gene whose effects are masked in the presence of a dominant gene. [ Allele ] - one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. [ Locus ] - a particular position, point, or place. [ Punnett Square ] - a square diagram that is composed of a grid of usually four boxes and is used to calculate and depict all the combinations and frequencies of the different genotypes and phenotypes among the offspring of a cross or breeding event.
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A - LOCUS
The A-locus is the “base” locus. Every rat in the world is AA, Aa or aa, with other colours existing as dilutes on top of agouti or black.
Agouti is dominant and denoted by a capital “A,” and black is recessive and denoted by a lowercase “a.” If the locus has a copy of both "A" and "a," the upper case letter will always come first, eg. Aa not aA.
A rat with one copy of Agouti and one copy of black (Aa) will display as Agouti. A rat with two copies of Agouti (AA) will display as agouti. A rat with two copies of the black gene (aa) will not have the Agouti gene at all, and will display as black.
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Black (aa) is easily identified because it is quite simply, black. The shafts of hair are solid from root to tip with no banding of colours. The shades can vary from jet black to a dark grey. Ideally the rat will be a dark, dark black. Black rats can also be prone to silvering that 'worsens' as the rat ages. It is technically a fault but many appreciate the look, and it is strictly aesthetic. A silvered black is genetically still just aa.
Agouti only varies slightly between heterozygous and homozygous visually, and it can be difficult (or impossible) to discern whether an Agouti is Aa or AA without test breeding. The shafts of hair on an Agouti rat have three bands of colour from root to tip, with the base being a slate colour. Agouti are a rich red-brown with clear demarcation lines on their midlines, where the colour fades to a silver-grey belly.
Aa – Heterozygous Agouti (one copy) and heterozygous black (one copy), when bred a rat with this genotype has a 50% chance of passing on 'a' black, or 'A' agouti to each baby.
AA – Homozygous Agouti (two copies), when bred a rat with this genotype will always pass 'A' to every baby. An AA rat cannot produce black babies.
aa – Homozygous black (two copies), when bred with this genotype will always pass 'a' to every baby. When bred to another 'aa' (black) rat will produce 100% 'aa' (black) babies. When bred to an 'Aa' (het agouti/het black) rat, every baby has a 50% chance of being 'aa' (black) or 'Aa' (agouti.) When bred to a homozygous agouti (AA), every single baby will be 'Aa' (agouti.)
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CALCULATIONS USING PUNNETT SQUARES
aa x aa = aa (100%) Aa x aa = Aa (50%) / aa (50%) Aa x Aa = Aa (50%) / AA (25%) / aa (25%) AA x Aa = Aa (50%) / AA (50%) AA x AA = AA (100%)
aa = black Aa = agouti het for black (carrying black) AA = homozygous agouti
Link to Punnett Calculator: https://scienceprimer.com/punnett-square-calculator