The "B-Locus"

GENETICS POST #wcrgenetics "B-LOCUS"

• • • • • • • • • • • • • • • • • • • • • • • • • • •

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.

• • • • • • • • • • • • • • • • • • • • • • • • • • •

B - LOCUS

The B-locus is responsible for the brown or chocolate gene. The chocolate gene is recessive and denoted by a lowercase “b.” Because it is recessive, a rat needs to have two copies of the gene to be a visual chocolate. This is called “homozygous chocolate.” It is possible for a rat to carry chocolate, but not display any characteristics of the chocolate dilute. This is called “heterozygous (for) chocolate.” Chocolate is a single dilute, meaning it is not made from dilutes on multiple loci – only the base (black or agouti) and the chocolate gene on the B-locus.

Chocolate on black is called “chocolate.” Chocolate on Agouti is called “chocolate Agouti” [AFRMA/NFRS] or “gingerbread” [URC]. West Coast Rattery aligns with URC. Please note both names are acceptable and recognized.

Chocolate rats are a rich, deep dark chocolate colour. Much like black, they may display silvering as a fault. Gingerbread rats look much like cinnamon rats in shading, with medium slate at the base of the hairs and warm russet banding. The faded belly on gingerbread rats is lighter shade than that of standard Agouti. Eyes are black.

• • • • • • • • • • • • • • • • • • • • • • • • • • •

CALCULATIONS USING PUNNETT SQUARES

aa bb x aa bb = aa bb (100%) aa bb x aa Bb = aa bb (50%) / aa Bb (50%) aa Bb x aa Bb = aa bb (25%) / aa Bb (50%) / aa BB (25%)

Aa bb x Aa bb = Aa bb (100%) Aa bb x Aa Bb = Aa bb (50%) / Aa Bb (50%) Aa Bb x Aa Bb = Aa bb (25%) / Aa Bb (50%) / Aa BB (25%)

AA bb x AA bb = AA bb (100%) AA bb x AA Bb = AA bb (50%) / AA Bb (50%) AA Bb x AA Bb = AA bb (25%) / AA Bb (50%) / AA BB (25%)

• • • • • • • • • • • • • • • • • • • • • • • • • • •

aa = black Aa = Agouti het for black (carrying black) AA = homozygous Agouti

aa bb = chocolate aa Bb = black het for chocolate (carrying chocolate) Aa bb/AA bb = chocolate Agouti "Gingerbread” Aa Bb/AA Bb = Agouti het for chocolate (carrying chocolate)

Link to Punnett Calculator: https://scienceprimer.com/punnett-square-calculator

@UnitedRodentCommunity #wcrgenetics #alocus #agoutirat #brownrat #chocolaterat #unitedrodentcommunity #urc #urcbreeder #urcliaison

#westcoastrattery #wcr #ratsaspets #dalmatianrat #marblerat #tonkineserat #siameserat #hairlessrat #roanrat #merlerat #genetics

• • • • • • • • • • • • • • • • • • • • • • • • • • •

Photo credits to Shanleigh Blackburn Imagine Rattery • South Africa Thank you for sharing your images with me!