Good evening, I am interested in the genes that a dog carries and passes down, certainly with regard to colour.  We know that our bitch carries the tan gene, although her pedigree doesn't appear to have had any tan until 4 generations back.  My question is.... when does a gene become recessive and no longer likely to be thrown if mated with another dog which carries the tan gene.

Many thanks to anyone willing to enlighten me.

In simple terms (it is a bit more complicated than this, but the basics), a gene doesn't become recessive, it is either dominant or recessive. A recessive gene can be carried, and therefore can be unseen for generations (both parents must carry it for it to appear, but pups can inherit the gene from a parent that itself is a carrier without showing it -so you won't necessarily KNOW which dog carries what unless you can DNA test for it or test mate), a dominant gene is always present in the dog and cannot be carried and you only need one parent with it for it to appear.

a gene doesnt become recessite it is eith dominant or recessive. do you want to breed it out i dont understand, if it is recessive i would have thought that is would have been bred out, but then there could be other genes effecting the phenotype (how a gene is expressed). it is thought that the ticking gene has 5 genes effecting it, which is why it is difficult to breed out.

> if it is recessive i would have thought that is would have been bred out

no that is dominant, like the other person said it can be carried for generations you need two dogs(ect) with recessive genes for a puppy to possible have it.

What breed are we talking about here?

I had never seen a black and tan dog in Pomeranian's and about 5 generations down in our line one of our girls produced a black and tan girl. 

The OP is talking about Cocker Spaniels I believe.

How do you know for sure you're bitch carries the tan gene if there have been no visuals born for 4 generations, have you colour tested or are there markers which point to a suspected carrier status?

Take a look  at VetGEn USA website as they do explain colour genetics better than I could that's for sure lol.  We collected samples for schipperkes a few yrs back which have proved useful to say the least as we have the blue gene which has the potential to be fatal.

http://www.vetgen.com/canine-coat-color.html

> How do you know for sure you're bitch carries the tan gene if there have been no visuals born for 4 generations, have you colour tested or are there markers which point to a suspected carrier status?

Maybe she's had a litter? I have a boy who carries tri despite there being no tri behind him for quite a number of generations - we discovered this when he sired a whole litter of tricolours!

People are oftne surprised by this in Yankees too, as the tan gene is masked in buffs, so whilst you may have/mated your bitch to what you think if a Buff, it may actually be a buff and tan as the tan is invisible in the buff colour,  and a black bitch carryign the tan gene pops out black and tan pups against the owners expectations of an all black or buff litter.

I was checking the BRS for the current quarter and noticed that her sire had just thrown a blue roan & tan, the first sign of tan in any of his litters to date.  From this I am making the assumption she is carrying the tan gene two as I've been told to produce tan, both dogs must be carrying the gene for tan.

Not sure if I'm missing some info here, but from what I've read I don't think you have enough information to assume she's carrying tan (unless you have indeed had her tested, or had a litter).  For the sire to be carrying tan, that only means he has one copy of the tan gene variant, and one copy of another colour variant (dogs are 'diploid' which means they have 2 copies of each chromosome and therefore gene, one from each parent).  If the sire is just a carrier, there is a 50% chance that he will have passed the tan variant to your girl.  Sorry if I'm being patronising and you know all this already, I may be missing some crucial info here (knowing very little about tan in Cockers!). 

I'm not feeling patronised at all, happy to be gleaning from every one else's knowledge as I'm very new to all of this. Thanks to all so far.

You can get her tested to find out for sure, with our schipperkes there isn't a specific black and tan test for the breed but it is possible to test for the tan gene, which is being done in Europe as there are several Black and tan's appearing and being bred.

You're best bet it to email VetGen to ask what information they can give you if you go ahead and test her, its just a couple of buccal check swabs and  a few $'s to tell you where you stand on her colour genetics.

Thanks to all for your advice, I knew genetics was complicated but I think I've got a lot of learning to do still

if you go in to a book shop and find a GCSE text book (biology) and have a read you will get the basics in that. oh dont buy it read it in the shop.

its when phenotypes and genotypes come in to it. but even with that, a book is best.