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Sewing bee genetics

 
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guy
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PostPosted: Tue Aug 02, 2016 8:55 am    Post subject: Sewing bee genetics  Reply with quote

Genetics of coat colour as told by The Sewing Bee and Captain Slow.


The instructions on all things animal are carried on a special chemical known for short as DNA.  This is a very long molecule called a chromosome that in turn can be divided up into short pieces that have been named genes.  Imagine (and here is the sewing bee bit) a zipper.  The whole zipper represents a chromosome and each tooth a gene. With this analogy you can see that every position on the zipper has two teeth - one on each side.  When it comes to reproduction the zipper is unzipped and rezipped with a corresponding piece from the other animal involved. Consider the chromosome that controls the sex of the animal.  This chromosome when viewed under a microscope is visibly different from the others such that each side is also named - one side X and the other Y. It will be female if it has two copies of XX and male it has an X and a Y.  At reproduction the male X can re zip with either of the female Xs and make a female or the male Y can rezip with one of the female Xs to form a new male.  This illustrates how easy it is to trace some things back a generation.  Every male pup has the same Y chromosome as its father, which came in turn from his grandfather.  Likewise if the pup is a girl then one of the Xs came from the father who inherited it from his mother (he cannot have any of his fathers X chromosomes as the father donated the Y.)

Parking that idea of genes as teeth on a zip for a  moment let us now go to a car show room.  You want to order a new car and are looking at the list in the back of the brochure.  There is a variety of qualities and levels of extras available and a number of standard and special colours.  The answers you give become the instructions to the manufacturer - a bit like each gene is an instruction in the manufacture of the new puppy.  The 'instruction' for paint colour can be equated to a 'gene' black, red, blue, green, or metallic could all be 'genes' but there is more, whilst the DVLA only specify colours in such a manner the manufacturers offer a number of different options - for green you might have mint green, apple green, brunswick green or british racing green.  Each of these are the equivalent of alleles of the gene green paint.  So far so good - but there is also a hierarchy to these paint colours, you cannot have any paint on any car - if you choose 'metallic' the manufacturer limits your choice to some of the more expensive models; so it is with alleles - you can only choose one and there is a hierarchy that denies you some options in the puppy if you have that colour. Imagine also you are in the showroom choosing your car with a friend.  You would like one colour but your friend thinks you should have another - as you are paying your decision is the one that counts; you are the dominant when it comes to choosing.  

Brittanys have four genes that control coat colour known as E, K, B and A.  E controls the expression or not of colour although the E is short for Eumelanin which is the pigment that you will see and which by default is black, when the recessive e is only present you get orange dogs remember the zipper and dominance - there are two copies of the gene at any one point, an Ee will be coloured just as much as an EE - hence mating orange dogs (ee) to orange dogs will only ever produce orange dogs. K (blacK) and B (Brown) are pretty self explanatory whilst A (Agouti) is responsible for the possible position of colour on the hairs; present in many animals as it is this effect that so aids camouflage. Mention earlier was of alleles - Each of these genes has some alleles that we know of.  E for instance has a mask allele (so once again you can determine certain things; an orange dog cannot carry the mask allele as it is not E. K influences B making the pigmented areas brown or liver instead of black, a dog carrying b might show a brown nose with a black coat for instance (white is not 'white' but 'no colour').  Agouti is a gene that interests Brittany owners as this has a number of alleles.  y- sable, t-tan points (tri colour to you and me) and lastly a- recessive black; the wild type w which produces the agouti banding is not present in Brittanys nor is the br- brindle which is also at this gene.  There is a hierarchy to these alleles y over t over a.  Thus a dog that is ay will be sable just as a yy dog and an at would be tricoloured.  An aa recessive black dog is the very rarest Brittany coat colour.  Sable is an interesting one as there is 'clear sable' and 'tipped sable' (we don't have banded sables in Britts).  Clear sable is a dark orange colour (the french often refer to this as 'out of standard orange') which may display dark tips as a pup but these grow out (according to Dr Makki) and tipped sable - a dark orange hair with a black tip (this is the one we tend to call sable and the French charbonne).


Further reading
http://www.doggenetics.co.uk/ has a lot of information on these and other coat colour genes

https://www.vetgen.com/canine-coat-color.html has a useful flow diagram, although complicated by the brindle.

PS for non UK readers The Great British Sewing Bee is a sewing competition that is very popular on the television and Captain Slow was a nick name given to one of the presenters on a very famous (here) TV programme about cars - Top Gear
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Victoria
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PostPosted: Wed Aug 03, 2016 10:15 am    Post subject: Reply with quote

Thank you, Guy...


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