Clarificaiton--Crossing parent to offspring vs. crossing 2 siblings

[JohnLongIsland]

I've read in a number of sources that inbreeding 2 siblings can be employed to try and stabilize some desirable trait, but that used extensively, offspring can start exhibiting unwanted characteristics (immune system health, physical health, etc). Three sources said that breeding a parent to an offspring was safer in the long run.

I'm curious if someone could comment on this. I realize the very safest way is to not cross closely related animals in the first place, but I also realize that inbreeding is very common when developing new breeds or stabilizing a trait within a breed.

I'm just trying to learn more about breeding, and in particular, how people go about breeding when they are trying to bring something back from the brink of extinction. Those cases where there are just a few birds left.

Thank you for any insights.

 

[MysteryChicken]

I'm just trying to learn more about breeding, and in particular, how people go about breeding when they are trying to bring something back from the brink of extinction. Those cases where there are just a few birds left.

In the case of Malays, a breed almost extinct in the US, & genetic diversity dwindling, they need to be bred to unrelated bloodlines, or crossed with another breed to increase genetic diversity.
After being crossed, it's important to back cross to the purebreds to restore traits. But unrelated stock, there's no need for the back crossing, just rebreeding the offspring from unrelated X Original to original will add genetics diversity too.

 

[DarJones]

Your basic question seems to be what effect inbreeding has and how to mitigate.

Inbreeding is deliberately mating closely related individuals with the intent to stabilize specific traits. It is currently the only effective method for developing stable lines meaning lines that breed pure for specific traits. The problem with inbreeding is it also concentrates undesirable genes. Once the undesirable genes are in a population, the only way to get rid of them is to bring in uncontaminated genetics. As an example, I can tell you of several highly desirable traits concentrated in Silver Laced Wyandottes, but I can also tell you that there are problems with the 4 variants of the slow feathering gene. Silver laced Wyandottes require at least one of the slow feathering genes to develop good lacing. The problem comes in when the most extreme slow feathering variant is present because young chicks up to 2 months old have very few feathers on certain parts of their body.

Mitigating the effects of inbreeding - specifically with chickens - requires growing very large numbers of chicks so the potential for selecting unaffected offspring is higher. This is a strategy often used with pure lines where crossing back to a parent produces highly desirable chicks but also gives several with defects. There is a reason pure bred chickens are often described as "raise 100 and keep 10 chicks". The combination of selecting for specific traits at the same time as selecting against deleterious genes requires large numbers.

There are several breeding methods that can be employed to minimize inbreeding effects. Look up cross breeding, line breeding, outcrossing, etc. https://en.wikipedia.org/wiki/Inbreeding

One very interesting possibility that is not yet viable for animals is development of doubled haploids. This is feasible with some plants where for example a pollen cell that is haploid is induced to double making it diploid then induced to form a plant and reproduce. A plant of this type is 100% homozygous with the exception of a few minor transcription errors. What if a doubled haploid chicken could be produced? It would inherently have to be free of defective genes and would 100% reproduce true to type.

 

[JacinLarkwell]

I think the very basics are that full siblings are 100% related to each other, but that parents are only 50% related to each of their offspring (unless they also share a parent, but I see that as more complex than very basics)

 

[JohnLongIsland]

In the case of Malays, a breed almost extinct in the US, & genetic diversity dwindling, they need to be bred to unrelated bloodlines, or crossed with another breed to increase genetic diversity.
After being crossed, it's important to back cross to the purebreds to restore traits. But unrelated stock, there's no need for the back crossing, just rebreeding the offspring from unrelated X Original to original will add genetics diversity too.

I think this is what I meant to ask. Let's just say in an absolute worst case. It's the Apocalypse, and you have exactly 1 rooster and 1 hen. You make the first cross (the only cross you can make). In the next step, would it be more wise to cross the siblings, or to cross the parent to the offsping? Some sources I read made a point that the parent/offspring cross was less prone to genetic problems. But it isn't clear to me why it should make a difference.

 

[MysteryChicken]

I think this is what I meant to ask. Let's just say in an absolute worst case. It's the Apocalypse, and you have exactly 1 rooster and 1 hen. You make the first cross (the only cross you can make). In the next step, would it be more wise to cross the siblings, or to cross the parent to the offsping? Some sources I read made a point that the parent/offspring cross was less prone to genetic problems. But it isn't clear to me why it should make a difference.

You can go both ways, first by breeding the offspring together, or then taking the first offspring, & breeding back to the parents. Go back, & forth with it to simply.

 

[sdm111]

I think this is what I meant to ask. Let's just say in an absolute worst case. It's the Apocalypse, and you have exactly 1 rooster and 1 hen. You make the first cross (the only cross you can make). In the next step, would it be more wise to cross the siblings, or to cross the parent to the offsping? Some sources I read made a point that the parent/offspring cross was less prone to genetic problems. But it isn't clear to me why it should make a difference.

If you have the choice then line breed. That is mom-son, father-daughter. In breeding is sister brother. What will usually happen is the offspring will start getting smaller and a tell tale sign of tightly bred fowl is small size and tilting of the tail. An option is to infuse new different blood that closely resembles your breed then outcross (breed the infused offspring back to the pure parent stock to get sizeable vigor back. In the gamefowl world its done often. Also in this world two of the same breed but of different families is still considered a cross. Anything brought in that specific family weather same breed or not is considered crossing.
I wouldn't really worry about in and out crossing of different breed unless absolutely necessary and focus on line breeding
Like mystery said

 

[sdm111]

Infusing of different breed you will from time to time get one that looks like the infused breed called a throwback. Obviously you don't want to use that for breeding but they are usually cherished in the gamefowl world as good luck. Just this year breeding my kelso gamefowl I had 1 look just like a redquill at hatch. That's a throwback, somewhere down the line one of my broodfowls got an infusion of redquill. I believe itsa good move to bring back the vigor and to make the offspring faster which is a redquill trait.

 

[Amer]

Here’s the thing about inbreeding. It is simply multiplying the traits you already have. Inbreeding is fine in the instance that you have birds that don’t carry any defects, but inbreeding will bring to light any nasty recessive traits your birds have. It also can enhance any good traits your birds have. So people often can inbreed very good and healthy birds, but in rarer breeds that aren’t great quality, you can bottleneck the breed and cause it to weaken.
A population can have low diversity and be strong, but only if the breeder first has taken a diverse population and weeded out harmful traits.

 

[sdm111]

Here’s the thing about inbreeding. It is simply multiplying the traits you already have. Inbreeding is fine in the instance that you have birds that don’t carry any defects, but inbreeding will bring to light any nasty recessive traits your birds have. It also can enhance any good traits your birds have. So people often can inbreed very good and healthy birds, but in rarer breeds that aren’t great quality, you can bottleneck the breed and cause it to weaken.
A population can have low diversity and be strong, but only if the breeder first has taken a diverse population and weeded out harmful traits.

X10. Any, ANY offspring with any defects must be culled. Like said you will just make it worse and worse