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How to Write the Genotype for a Black-and-Tan With Merle Markings

Border Collies and Australian Shepherds are at the forefront of dog breeds that can have merle markings on their coats. Other breeds that produce merles are the Rough and Smooth Collies, Dachshund, Great Dane, Shetland Sheepdog, and Cardigan Welsh Corgi. (ref. 2) The list is not inclusive, as merle markings can be bred into the breed (and have been recently in some, like the Chihuahua). Coat colors, as with everything else, rely on genetics, specifically the genotype. A black-and-tan dog with merle markings has a specific genotype to produce those colors.

Instructions

Writing the Black-and-Tan With Merle Genotype
- 1
  Write out the word "Black" and end it with a colon (:). Beneath it, write out four combinations: EEBB, EeBB, EEBb, and EeBb. It should look like this when finished:
  
  Black:
  
  EEBB
  
  EeBB
  
  EEBb
  
  EeBb
  
  These are the four ways to note that a dog has a black, bicolor, tricolor, or blue merle coat with a black nose. E's represent no mask or recessive red colors while B's represent liver color (there is none showing).
- 2
  Skip a little bit of room beneath the last genotype and write out the word "Tan." Follow it with a colon (:) and then beneath the word write out the following genotypes: kk. It should look like the following:
  
  Tan:
  
  kk
  
  a^t a^t
  
  a^t a
  
  In some breeds, this will also be called "tricolor" as the tan and black come with white. A large K, even one, makes the coat black instead of tan. kk is the only combination (on the black genes) that allows for tan markings. Tan points are most common. Note that the t's are superscript (like the degree mark in temperatures) while the a's are not.
- 3
  Write down "Merle" next and follow the above directions to set it up. The genotypes for this coat marking is Mm.
  
  Merle:
  
  Mm
  
  Note there is no MM or mm form of merle, as these have been noted as lethal combinations of genes.
- 4
  For simplicity's sake, assume that all visible markings and colorations are homozygous and what is necessary to produce them (in the cases where homozygous pairs will not). A homozygous pair is one that has two big letters, or two little letters. Heterozygous is one big and one small.
  
  For example: BBCCDDEEggMmSSKK is a genotype for a black dog with merle markings and no white. Broken down, you have: BB (no liver color), CC (no albino), DD (no dilution), EE (no mask or recessive red), gg (no graying), Mm (merle), SS (no white spotting), and KK (solid black color).
- 5
  Use the above example and write it down. Erase the KK and make it kk to show that the dog can express a tan color. After the KK, write down a^t a^t to show that there are tan points of some form on the dog. The result is BBCCDDEEggMmSSkka^ta^t. This is the genotype for a black and tan with merle markings. If white is also spotted on the dog, then the SS should become ss.

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