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How much does outcrossing improve genetic diversity?

Discussion in 'Dog Discussion' started by Institute of Canine Biology, Jun 28, 2018.

  1. By Carol Beuchat PhD
    Even 100 years ago, breeders of domestic animals realized that continuous inbreeding resulted in deterioration in the quality of their stock. To remedy this, every few generations a relatively unrelated animal would be crossed in to the population to freshen up the gene pool and reduce the level of inbreeding. In fact, the coefficient of inbreeding was devised in the 1920s as a way to estimate the level of inbreeding so breeders would know when it was time to do an outcross.
    Many modern dog breeders follow a similar regime, breeding close for a few generations then out to a relatively unrelated dog. But is this as effective as we think it is?

    For one thing, our dogs are much more inbred than they were a century ago. Many breeds have average levels of inbreeding above 20%, and too many are even higher. With such high levels of inbreeding and low genetic diversity, the dogs in a breed can all be more similar genetically than half- or even full siblings - or even more. How much can you expect to gain from an "outcross" that really amounts to close inbreeding?
    One way we can get an idea of the potential benefits of an outcross is by using simple mathematical models of population genetics (Windig & Doekes 2018).
    Researchers simulated various outcrossing strategies for the Saarloos Wolfhond (a cross between a wolf and German Shepherd created in about 1935) and an unrelated "donor" breed. The Saarloos Wolfhond has been a relatively small breed since it was founded, with about 25 litters produced per year and high rates of inbreeding. In the last decade or so, genetic disorders have become a problem and signs of inbreeding depression (smaller litter) have appeared. Because of this, an outcross project was started in 2016.

    The study assessed the consequences of four types of crossbreeding schemes on population inbreeding.

    1) A single outcross with no backcross;
    2) A single outcross with backcross
    3) Repeated outcrosses with backcrossing;
    4) Continuous outcrossing.

    For each of these scenarios, they ran multiple simulations to produce information on the degree of variation that might be produced in a real, randomly breeding population.

    The F1 from a cross of the recipient (Saarloos) and the unrelated donor breeds had an inbreeding coefficient of 0%.


    [​IMG]
    They found that a single outcross followed by one or more generations of backcrossing reduced the beneficial effect of the outcross and sometimes even increased the rate of inbreeding. In the cross breeding, the first generation receives 50% of alleles from each of the donor and recipient parents. But in subsequent backcrosses, half of the donor genes are lost on average, so that after a few outcrossings the remaining donor contribution was consequential.

    This result is not unexpectded, but it should give pause to those that design a crossing program that consists of a single donor cross followed by serial backcrosses. Kennel clubs typically want about 3 backcrosses before admitting the descendants of a crossbreeding program to the studbook, but required backcrosses essentially flushes the donor genes from the recipient gene pool and there is no net benefit.

    There are multiple examples of crossbreeding programs that failed or produced little benefit because the introduced genetic variation was subsequently lost.
    The scenario of repeated outcrossing generally reduced the rate of inbreeding, but the inbreeding rates were highly variable, and in some simulations all of the donor genetic contribution was lost.

    Regular outcrossing was the most effective strategy for reducing the rate of inbreeding in the Saarloos Wolfhond, but still the outcomes of the simulations were highly variable.
    What this study clearly showed is that using outcrossing to reduce the rate of inbreeding requires careful management in order to ensure success, and the benefit achieved will be small unless crossing is done on a regular basis. One key to success was to follow outcrossing with strategies to increase the effective population size or inbreeding will quickly return to previous levels.

    This outcross simulation used a completely unrelated breed as a donor. For breeders that are crossing to what they hope are relatively unrelated dogs in their own breed, the benefit will be much less if the level of relatedness among individuals is high.
    The authors of the study also addressed an issue often raised by breeders in discussions of outcrossing, specifically
    "the unwanted introgression of (unknown) deleterious alleles from a donor breed is often used as an argument against outcrossing. Since probably all animals carry recessive deleterious alleles, this may indeed be the case. However, the opposite, introgression of beneficial alleles is possible as well. The chance that different alleles are present in the donor breed depends on how closely related the breed is." (Windig & Doekes 2018)
    This study highlights the difficulty in reversing the effects of inbreeding and loss of genetic diversity in closed populations of dogs. While simple in concept, genetic rescue is complex and challenging, and undertaking a program without an effective plan for maintaining the added diversity will likely achieve little. Fortunatly, the efficiency and chance of success can be improved using "genomic-assisted selection". For this, microsatellites (STRs) have largely been replaced by next-generation sequencing using high-density (> 100,000) SNP genotyping, which produces vastly more detailed information at a reasonable cost.

    The cutting-edige technology as well as the necessary expertise to design an effective outcrossing program is available now to dog breeders, offering the possibility of reducing the burden of genetic disorders in dogs in future generations.

    Ironically, the modern solution to the problem of genetic disorders in dogs goes back to the time-tested method used a century ago of the regular introduction of new genes into the gene pool. These days, the process is more difficult because the levels of inbreeding are very high, but we can improve the chances of success using population genetics and genomics.
    ................................................​
    You can enroll your breed in the new ICB Genomic Management Workshops, in which breeders and expert scientists will work together to assess the genetic status of the breed and design effective breeding strategies to reduce inbreeding, increase genetic diversity, and improve the health of dogs.

    We are accepting breeds now, so don't miss this opportunity to be one of the first we work with. You can read more about the program HERE.

    And don't miss out on our "Incentive" offer of a free course for each participant for the first three breeds enrolled!

    REFERENCES

    Windig JJ & HP Doekes. 2018. Limits to genetic rescue by outcross in pedigree dogs. Journal of Animal Breeding and Genetics 135:238-248.
    To learn more about the genetics of dogs, check out
    ICB's online courses

    ***************************************

    Visit our Facebook Groups

    ICB Institute of Canine Biology
    ...the latest canine news and research

    ICB Breeding for the Future
    ...the science of animal breeding

    Continue reading...
     
  2. Jacob

    Jacob Top Dog

    I just love this science shit. You got this Canine do a breeding and put me on the list for a pup. No human aggressive dogs. Just good well rounded athelete from deep game dogs.
     
  3. wicked13

    wicked13 CH Dog

    Your a dumb fuck u need a poodle
     
    c_note and Holocaust like this.
  4. Jacob

    Jacob Top Dog

    Yeah I know just put anything together and then raise it those little boxes for 10 hours. You got anything real to bring or you think being dumb is in
     
  5. wicked13

    wicked13 CH Dog

    Yeah dumb ass you were talking to a bot .
    Your slower then turtle shit
     
    Holocaust likes this.
  6. Jacob

    Jacob Top Dog

    Hey why don't you go play with all the other teenagers games like fortnight you get to swear and stay up late it's great for your age group
     
  7. wicked13

    wicked13 CH Dog

    Lol na I prefer to learn from your genius self
     
  8. Holocaust

    Holocaust Match dog

    Those "little boxes" are called "above ground pens". They're on every dog mans yard just like chains... they're used to keep in heat bitches where they cant get bred, puppies and the dam in a safe place, hurt or sick dogs a safe, clean place to recuperate, and for dogs in keep to get rest time...

    If you've never seen one or dont know what they're used for you shouldnt comment on them or definitely not take sideways shots at them. Only shows how little experience you have....
     
    c_note, DISCOIII and bks like this.
  9. Holocaust

    Holocaust Match dog

    And before you attack me and my "shitty dalmatian/american bulldog/razors edge bully mutt" again, we know you know better, have better, have done more, and your great great great grandpa and you both beat Earl Tudor twice. It's a true privilege to be able to read your amazing knowledge filled comments. I'm seriously surprised anyone ever kept a dog alive before you and your expertise came about..
     
  10. Jacob

    Jacob Top Dog

    Yeah they used those boxes for what you said. Thing is YOU don't use it for that. I think that's how you roll.
     
  11. Jacob

    Jacob Top Dog

    You might be thinking I'm someone else. I've never said anything close to that. In any case you seem to want want to control all conversations across the board with all the members. Unless you don't have good points on nutrition or breeding or kennel setups you could go to Facebook for all your drama style attitude
     
  12. Holocaust

    Holocaust Match dog

    Dude I give you the props you want then you tell me what I do???

    You're just a rude miserable pet owner who comes here to play some fictional internet character and run people and their dogs down.

    You're the childish loser who has yet to contribute anything productive in the way of nutrition, housing, husbandry or really any aspect of owning, breeding, or performing with a bulldog. Quit flipping that around.

    Now if you want to keep on with the childish, unfounded lies you're spreading about me and my animals on the internet you can grow a set and take me up on the offer I already put out.... Otherwise shut the fuck up, quit attacking your betters, and be the good little shit green know nothing everyone knows you are... who knows maybe you'd actually fucking learn something then.
     
  13. Holocaust

    Holocaust Match dog

    Offer kenneling advice...

    You mean the whole thread about my "tiny box" that got more comments and likes than your post about your puppy? The same thread I offered the plans, sources, and any advice needed?

    Offer nutrition help..

    You mean like the whole thread @bamaman made saying I privately contacted him to help him source high quality feed for a better price in his state?

    Again Jacob please stop lying about me and my dogs. It is the lowest thing a person in dogs can do is outright slander a man and his dogs.

    If its jealously over likes or knowledge or popularity I'm sorry you're hung up on it. I'm not. I'd be willing to help you learn if you wouldn't attack me and my dogs because I(or anyone else) wont agree with your theory on the 2 hours alone nonsense.

    If you cant stop attacking me and my dogs but dont plan on physically meeting up you need to run to fb with your drama and leave the forum to ppl who want to learn, teach, and interact without your attacks and drama.

    You're the problem not me. That's why you're in this thread arguing with wicked but you attacked him by dissing me, my above ground pen, and my dogs... I wasn't in the convo til then. And I didn't even say anything shitty after you attacked me AGAIN.

    You have a serious mental health issue I think. If you get your meds sorted, apologize for attacking me and my animals I'll be willing to try to help you learn. If you're not willing to do that and still want to slander me, my animals, and our characters please have the common courtesy and courage to do it to my face not on the internet like a child.
     
  14. Jacob

    Jacob Top Dog

    Your the best. Dumb game but it works. Hey tell me again about How you don't know how to talk to Authority. That shit keeps me alive.=)):))=)). You mention the Likes and in the same breath say it dosnt really matter to me. Your one of those women that get boob jobs and live of the likes.=D>. Don't change bud make your little setup work and show that determination and a quarter brain is all you need. There are lots of good dogs that lived in crates but mine never will and RAW is what I feed and don't think I haven't fed the cheap shit when I was young guy. Check out this old bad ass. 14 and still does that 20 min a day. That's a huge pool and he does about 30 laps.
     

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  15. Holocaust

    Holocaust Match dog

    Dude the best thing you could do is kill yourself... seriously. The world can see this and it doesnt look good..
     
  16. Holocaust

    Holocaust Match dog

    Did you just brag on the man eater you had put to sleep? Lol
     
  17. AGK

    AGK Super duper pooper scooper Administrator

    Jacob js gone. I do not have the patience for shit starters anymore or cleaning up nonsense threads. I've let it carry on long enough. He don't contribute anything of value to the board therefore he has been shown the door.

    Carry on......
     
    DISCOIII and Holocaust like this.

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