brother/sister mating ok?

[jvls1942]

Quote:
WOW!!! Sounds just like Judge Judy!!!

I like judge Judy.. I'll take that as a compliment..

 

[curliet]

Was just about to post a response to this thread regarding cranky, opinionated and argumentative members, but then thought better of it.
Instead I'll mention that the thread itself as very interesting, we hope to be doing some hatching one day soon, and it's great to know that there are several people here with knowledge about the genetics aspect of things. Thanks all, for the info.

 

[seriousbill]

Here's a post from a poultry geneticist on another board:

In general inbreeding is not good. It is used because it is the most effective means of fixing complex genetic interactions (multiple genes affecting some trait under selection). Breeding back to a good sire or dam will increase the likelihood of passing the genes that make that sire or dam superior onto the offspring in the same combination that the parent has.

The bad comes in when you think of genetic load. Each of us and every chicken has a number of recessive lethal and detrimental alleles. For humans the genetic load is around 2.5 (it is higher for chickens). This just means that each of us has around 5 recessive lethal equivalents in our genomes (5 recessive lethal genes). We say equivalents because you actually have many more detrimental genes than this, but they are not fully lethal when made homozygous, they just lower your viability (make you weaker or more susceptible to disease). This is why close relatives should not mate. The detrimentals start showing up in the progeny.

We tolerate this for animals because we can cull the ones that don't make the grade, and you get many perfectly health birds from matings like this. The danger that we face is that the likelihood that we will eventually lose the line due to inbreeding depression is increased. Birds will look healthy, but fewer eggs will be laid and fewer eggs will hatch. With intense selection you can beat inbreeding depression, but few backyard breeders can afford to do this.

A little inbreeding is OK, but I wouldn't want to base my whole flock on two sibs. Half of each of their genetic loads is shared between them. Mating them together gives a 1/4 chance of making any shared recessive detrimental homozygous and expressing it in the progeny. If you keep breeding from the descendents it is more likely that recessive detrimental (not fully lethal) will become fixed due to random chance and the viability of your line will decrease. You have to bring in new blood (the dominant allele) from another line in order to increase the fitness of your line.

I used to inbreed my backyard birds. You can't avoid it if you are breeding for specific traits and you only have one backyard. Probably everyone that has bred chickens for a decent period of time has come across a line that was too inbred and could not be reproduced efficiently. I have research lines right now that have less than a 30% hatch rate. It is very difficult to maintain these lines, and if I were a backyard breeder I'd be looking for another line with the traits I needed to bring in new blood.

Unfortunately for me I can't do this for the research lines because if I brought in new genetics I'd lose the value of the highly inbred line (they are nearly genetically identical) Right now it is like crossing identical twins for one line (+99.9% inbred). We use these lines because when we do outcross these birds we can do the same cross next year and get the same result (the genetics stay the same). So the repeatablilty of our experiments is better than if we used non inbred lines whose genetics could change every year.

We don't really understand hybrid vigor. We can guess that when two lines do not share the same detrimental recessive loci (aaBB, AAbb) that crossing these two lines will create dominant heterozygotes (AaBb) that are not affected by the recessive trait and so do much better, but we don't have much of an idea of what genes these are or what they do. The more you outcross the less likely that you will create the recessive homozygotes, but you are also less likely to create the combinations of genes needed to perfect the traits that you are interested in. Most selective breeding is a trade off between inbreeding and maintaining some genetic diversity so that you can minimize inbreeding depression.​

 

[Wynette]

This is interesting (and very helpful) info.!

Who is the author? I'm curious as to if s/he is any type of poultry professional, or just someone who has noticed and studied this issue. Regardless, thanks for posting, seriousbill!

 

[Jenski]

Gail Damerow has a whole section on breeding / genetics in Storey's Guide to Raising Chickens. Some of the material echoes what our experienced breeders in this thread have said. The book is definitely worth a read if you're considering breeding.

 

[Wynette]

Thanks, Jenski. I have her Chicken Health Handbook and look to it often. I'll pick this book up as well.

 

[seriousbill]

Quote:
Yes, he is a genetics specialist. His name is Okimoto. He used to work for the U of Arkansas, but now he's in the private sector, I believe. This material is from a public post, so I doubt he'd mind my naming him for proper credit.

I sure wish he could be persuaded to post here on BYC!

 

[Wynette]

Thanks, serious. You know, I've often thought it would be neat if we had available on BYC experts in certain areas that we could get feedback from, but if that was the case, I'm sure those folks would be doing nothing more than answering questions all day!

 

[North Briton]

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