Which is better breeding back to parent or breeding siblings?

[Joe Massey]

Hi guys!

Which is better breeding back to parent or breeding siblings?

[dr del]

I may well be wrong but I think, genetically, there would be more chance of diversity between a parent and offspring than between siblings.

[grcforce327]

I may well be wrong but I think, genetically, there would be more chance of diversity between a parent and offspring than between siblings.

Isn't common sense a wonderful thing.

[dr del]

Isn't common sense a wonderful thing.

Not really.

Between the parent and offspring should be a difference in 50% of the genes present.

But in siblings it could be in 0-100% of the genes.

Err .... I think.

[CrazyPiston]

I agree with dr.del the second time.

50% of an offsprings genes would be the same as the parent as thats where they came from. However each offspring gets a different combination of genes, even though they came from the same parents. Thats why they dont all look identical.

I also agree that the sibling genetic differance can vary from 0% - 100% , but with parent to offspring your guaranteed 50% the same.

Which breeding would be better, parent to offspring or siblings... I think its a crap shoot. You could think that siblings would offer more diversity, but maybe the siblings that you want to breed are 75% identical. So in that case breeding to a parent would offer more diversity. But about the time you decide that the siblings will only be 25% identical.
Kinda like playing the lotto?

Thank you for this thread as I was wondering about breeding siblings, and the way you asked your question made me think of it differently.
But now I have a question of Would breeding parent to offspring or siblings (just once, not continual line breeding) cause great harm or is there enough diversity of genes in the ball python world that it would be ok?

[OhhWatALoser]

The pairing that both snakes are not heterozygous for negative traits. Doesn't matter if they are siblings, parents, or 50 generations removed. How "identical" they are is irrelevant.

[nightrainfalls]

In order to answer the op's question, is it better to breed a parent to a child or a sibling to a sibling, it is important to understand the probability of inbreeding depression. In other words, how likely is it that inbreeding will weaken the next generation in a measurable way.


To make it easy we will envision an organism with just one gene pair. This one gene has 4 genotypes A,B, a and b. The mother is AB and the father is ab. Using a punnet square, the offspring will be in a ratio of. Aa, Ba, Ab, Bb. Now let us note that BB is a homozygous negative trait. Any organism with BB will suffer a dramatically shorter lifespan. If we breed two siblings together, we could get many different results, but we should notice that only a very few pairings could produce BB. In fact only Ba x Bb could result in a BB genotype. We could work out all of the combinations or you can just trust me when I tell you there are 16 possible combinations and 2 of them result in inbreeding depression. We can reduce the ratio to 1 in eight sibling combinations can cause deleterious effects.


If we breed offspring to parents in this case, the mother can produce BB in about 1 out of two pairings. The father can never produce BB. So in this case if the mother and father reproduced equally with siblings we would find that one quarter of the pairings would able to produce BB genotypes. In this case it would be better to pair siblings with siblings than parents and offspring, but it would be better to cross offspring with the father than siblings with siblings. Even in this very simple case, the answer is ambiguous at best.


Here is the kicker, the numbers work out differently for every possible combination of traits. If the parents are Ab x Ab then BB can never happen and all pairings are safe. Try figuring out the other possible crosses by yourself. Use punnett squares. It isn't hard, but it takes a while.


http://en.wikipedia.org/wiki/Punnett_square


Now remember, there is no such thing as an organism with just one gene that has four genotypes. In reality the fitness of organsims is incredibly complex and the actual inbreeding depression in previously non inbred lines ends up being pretty low.


So in some cases it is better to breed siblings, but in reality, unless this math is done for every gene in the entire organsim, it is really difficult to tell which is best, and any difference is likely to be so small it doesn't really matter in the real world. The problems occur with sustained inbreeding over long periods, when deleterious alleles start to become concentrated. This can be especially dangerous if a desired trait is linked to a deleterious trait. Line breeding for the positive trait can quickly produce very unsound animals.


The ultimate answer to the OP's question is, well it depends, and it is probably such a small difference that it isn't important. Limit line breeding whenever possible, and out breed as much as possible without loosing the selected trait. As long as you keep the inbreeding to a minimum, the possibility of running into a problem is not high, and culling can be used to offset those problems.


David