Tuesday, July 12, 2011

Coat Color: Genetics

I've always wondered where Bruno's stripes came from. Many pit bulls can have brindle coats - and so can other breeds like Plott Hounds, Great Danes, French Bulldogs, Mastiffs, Boxers, Corgis and lots more.

(Bruno at the dog park)

However, some people have a bias against brindle-colored dogs, and that may lay in the genetics. For example, it is difficult for Mastiffs with brindle coloring to compete against Apricot and Fawn colored Mastiffs. My boyfriend's grandmother automatically disliked Bruno when she met him because of his "ugly Brindle coat." 

I decided to learn a bit about the genetics behind the bias:

First of all, many animals have stripes. It is generally agreed that stripes occurred over millions of years of evolution for camouflage purposes, however, dog coats can evolve must faster due to special extra genes that can mutate faster with human breeding.

 (see how well I can blend into my surroundings?)


Dog coat color, shape, and length genetics are based in 16 specific locations of the geneome.

The basic color loci are:
Agouti Locus (A), Brown locus (B), Dilute locus (D), Extention locus (E), Harlequin locus (H), dominant black locus (K), Merle locus (M), and Spotting locus (S).


Brindle is mostly determined on the Dominant Black (K) locus. In many brindle breeds, fawn is a recessive trait - so dogs need two recessive genes to be completely Fawn colored. Dark is the dominant trait and Brindle occurs when the pup recieves a dominant and a recessive gene.

If a pup recieves "K" and "kbr"- he will be black or  dark, and if he recives "kbr" and "kbr" he will be brindle. Also, if he recieves "kbr" and "k"  he will be brindle, but he will be light or fawn if he has "k" and "k."

In other words, if one parent is Black, chances are no dogs will be brindle because the "K" will be dominant, much like brown eyes in humans. Brindle is dominant over non-brindle- so if one parent parent is brindle and is bred with a dog that has no brindle ancestry- the resulting pups will be between 50% and 100% brindle. (100% if the brindle parent is not brindle recessive.)


Some brindle dogs will have a black face mark in the "eumalanin" color (sometimes also on the ears). This is caused by the presence of an "Em" gene on the Extension-locus.
The differences in color are controlled by pigmentation genes, but most brindle dogs' have "eumalanin (black)" stripes on a "phaeomelanin (red)" base. The wide diversity of brindle colors in the pit bull population is due to interactions between the B (brown) and D (dilute) loci which can result in black brindle, blue brindle, brown brindle, and fawn brindle.
Of course, Pit bulls and pit bull mixes can have extreme varieties in coloring from pure white, to piebald, to blue, to red to any mixture of colors.


In the past, "blue" pit bulls were seen to be very rare. Currently, back yard breeders use this precieved "rareness" to attract buyers, but there are actually a large number of blue-nosed pit bulls. This is so because the homozygous recessive alleles that cause blue-ness are (dd), so any dog with a (D) would not be blue. To increase the number of blue pit bulls, breeders had to breed blue pit bulls with other blue pit bulls which results in 100% blue or fawn/blue offspring.












See examples of each color pit bull here.
Read more about discovering the genetics of your dog here.

Sources:
http://www.chromadane.com/standardcoat.htm
http://www.adbadog.com/uploads/pdf%20forms/colorgenetics.pdf


9 comments:

  1. I LOVE brindle coats, this was really cool, thanks!

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  2. Very interesting! My dog (result of accidental backyard breeding in Georgia) is blue and his dad is brindle.

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  4. What about blue brindels?What would thier homozygous recessive alleles be?

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  5. Wow, this was actually really interesting! I've always loved brindle coats too, but I never really thought about the genetics of them. I really love seeing it broken out into specific genes, and combinations thereof, that lead to the brindle coat. Thank you so much for writing! http://ironkingkennels.com/forsale.html

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  6. I have a reverse blue brindle and he is amazing!!

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