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The "C-Locus" part two

  • Writer: RileyKat
    RileyKat
  • Jun 16, 2021
  • 5 min read

GENETICS POST #wcrgenetics "C-LOCUS, pt. 2"

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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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** C - LOCUS - ACROMELANISM

In this part, I will explain the "acromelanism" allele which covers both Siamese and Himalayan.

"C causes the dilution of both yellow and black pigment but each is affected differently. There are three known and a fourth suspected allele at this locus. Yellow pigment is completely eliminated by the third one, but black pigment shows a more gradual reduction, not being completely eliminated until the fourth allele." [https://www.afrma.org/ratgenpart1.htm]

Acromelanism is denoted by a superscript "h" - [ ͪ ]

Himalayan and Siamese look different depending on if they are red or black eyed, and if they are on an Agouti or black base. I am not touching on the BE gene in the C-locus series, so I am referencing RE Siamese for the remainder of this post.

aa CC - Black [full colour] aa Cc - Black [carrying albino] aa cc - Albino [black based] aa c ͪc - Himalayan [black based] aa c ͪc ͪ - "Seal Point" Siamese [black based]

Aa CC/AA CC - Agouti [full colour] Aa Cc/AA Cc - Agouti [carrying albino] Aa cc/AA cc - Albino [Agouti based] Aa c ͪc/AA c ͪc - Himalayan [Agouti based] Aa c ͪ c ͪ /AA c ͪ c ͪ - "Agouti Point" Siamese [Agouti based]

As mentioned in Part 1, "cc" Albino displays completely white with pink eyes. As soon as you add in the acromelanism gene, things become a bit different. "c ͪc" Himalayan are born anywhere from albino in appearance to a dirty cream. As they age, the body fades leaving darker points on the nose and legs. "c ͪ c ͪ " Siamese are born anywhere from a dirty cream to a dark golden brown, like a deeply toasted marshmallow. As they age, they also fade into points however they stay much darker and may retain the dirty, sooty look on their body.

Acromelanism is temperature sensitive. The colder the temperature, the darker and bolder the points on an Himalayan/Siamese rat.

This is fairly simple and straight forward so far. It's when we look at carrying the c-locus that things get a little more complicated and frustrating. C-locus can 'hide' in lines and pop up where they're least wanted. C-locus hides many other genes entirely, making them pointless. This can make pairings difficult!

It is recessive just like Albino but since we have the superscripts, our Punnetts look a little crazier. You can get a combination of base, Albino, Himalayan and Siamese rats in one litter if you pair the right rats together, but some combinations will produce ONLY Siamese.

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CALCULATIONS USING PUNNETT SQUARES There are duplicate combinations - just swapped around. I find it easier to look at it like this, where you have PARENT ONE be one solid variety (Albino, Himalayan, etc) and then you can compare every alternative gene with PARENT ONE.

Not specificying black/agouti base in these Punnett Squares, any of the below are Agouti Point Himalayan/Siamese if Aa/AA and are Seal Point Himalayan/Siamese if aa.

FULL COLOUR/ALBINO COMBOS cc x cc = cc (100%) cc x Cc = Cc (50%) / cc (50%) Cc x Cc = cc (25%) / Cc (50%) / CC (25%) cc x CC = Cc (100%) CC x Cc = Cc (50%) / CC (50%) CC x CC = CC (100%)

FULL COLOUR COMBOS CC x Cc ͪ = CC (50%) / Cc ͪ (50%) CC x c ͪc = Cc (50%) / Cc ͪ = (50%) CC x c ͪc ͪ = Cc ͪ (100%)

FULL COLOUR HET ALBINISM COMBOS Cc x Cc ͪ = CC (25%) / Cc ͪ (25%) / Cc (25%) / c ͪc (25%) Cc x c ͪc = Cc (25%) / Cc ͪ (25%) / c ͪc (25%) / cc (25%) Cc x c ͪc ͪ = Cc ͪ (50%) / c ͪ c (50%)

FULL COLOUR HET ACROMELANISM COMBOS Cc ͪ x Cc = c ͪc (25%) / Cc ͪ (50%) / CC (25%) Cc ͪ x cc = Cc (50%) / cc ͪ (50%) Cc ͪ x c ͪ c = Cc (25%) / Cc ͪ (25%) / c ͪc (25%) / c ͪc ͪ (25%) Cc ͪ x c ͪ c ͪ = Cc ͪ (50%) / c ͪc ͪ (50%)

ALBINO COMBOS cc x Cc ͪ = Cc (50%) / c ͪc (50%) cc x c ͪ c = cc (50%) / c ͪc (50%) cc x c ͪc ͪ = c ͪc (100%)

HIMALAYAN COMBOS c ͪc x Cc ͪ = Cc ͪ (25%) / Cc (25%) / c ͪc (25%) / c ͪc ͪ (25%) c ͪc x c ͪc = cc (25%) / c ͪ c (50%) / c ͪ c ͪ (25%) c ͪc x c ͪc ͪ = c ͪc (50%) / c ͪc ͪ (50%)

SIAMESE COMBOS c ͪc ͪ x Cc ͪ = Cc ͪ (50%) / c ͪc ͪ (50%) c ͪc ͪ x c ͪc = c ͪc (50%) / c ͪc ͪ (50%) c ͪc ͪ x c ͪc ͪ = (100%)

cc = Albino Cc = Full colour het for Albino CC = Full colour Cc ͪ = Full colour het for Acromelanism cc ͪ = Himalayan c ͪc ͪ = Siamese • • • • • • • • • • • • • • • • • • • • • • • • • • •

aa CC = Full colour [black] aa Cc = Full colour het for albino [black carrying albino] aa cc = Albino

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Photo credits to Aimee Sek at Once Upon A Mischief Rattery - https://www.facebook.com/onceuponamischief/ Meghan Burkhardt at Kinni Brook Rattery Taylor Sexton at Tale of Tails Rodentry - https://www.facebook.com/TaleOfTailsRodentry/ Thank you for sharing your images with me!

 
 
 

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