Breeding specific traits

[IngoVals]

Hello

 

This is my first post here and I'm looking to get some perspective on my thoughts. I only undestand basics in this field so when I started thinking more about I knew I had to get expert help.

 

My case revolves around the breeding of species, especially when breeding special traits in animals.For example you might breed a dog species to be really big. The tactic is to find a male and a female that are big so their offspring will be big as well. I started wondering why the offspring could however get bigger then it's parents.

 

Let's assume the trait is based on 1 gene and let's give it a value, with bigger values meaning bigger animals ( I know it's not simple like this and that's probably the answer but humor me).

 

If the size is base on the average of the gene values on animal had 7-5 the other 6-6 (so both effective size 6). The offspring could get 7-6 and later mate with sibling and that one has 7-7. But there it's reached the maximum in that family. However if one parent had been 10-2 the maximum would have been much bigger.

 

I know of course that we can't assume value and such. But let's say a superior mate (or equal) has reached the state of having a gene pair where both gene perform the same. At that time it's offspring can't surpass it.

 

So this must work very differently then I think. Is it so that there is a best gene for a given trait ( a one gene trait that is ) in that species and if you could get it to have both in the pair you've reached maximum?

 

Please don't laugh at me for simplifying it so much and help me understand how a trait can get exagerated in a inbred species. Is it just the fact that there are so many genes controlling each trait that there is always room for optimization or some explanation that is far off from what I'm talking about.

[skyhook]

This is what I think...

 

When you breed an animal and you are selecting for size. First you have a pair , and the pair produce many offsprings. Of these offsprings, I'm assuming there is natural variations in size , and there are a few that is slightly bigger than the rest and may exceed its parents. So you take the biggest and cross them. again, there is variations in size, and we choose the biggest and most vigorous and so on. There has to be many offsprings to choose from, to make it easier. It may work if there are offsprings that are bigger than the parents. I don't know if we can look at it as a "locus" thing. like maybe a Dalmatian dog pair is going to produce dogs of about the same size, with slight variations in size. It is unlikely to produce one the size of the chihuahua, although there is a small chance. This Dalmatian dog, I've seen a really big one.

 

but for some animals, inbreding can't go on for many generations. They need to be crossed to a related line occasionally.

It is said that hybrid vigor may caused some animals' offsprings to be bigger.

 

Maybe we take a look at another possibility. I assume there is a single gene that cause gigantic offspring indirectly. This gene is recessive and very few of the offsprings inherit it. If you by some luck, pick two animals that have this recessive gene, this is definitely going to get more giants in the next generation. So it is luck. If you paired one animal with recessive gene and one normal animal, the giants are probably going to be rare again. but in reality, the giant gene I assumed, could be a combination of factors, or it could be one.

 

by the way, I'm not a dog breeder, I kept betta splendens some yrs back.

[dttom]

Here you are performing an artificial selection to push the population size to the bigger size. I would not say being bigger would be due to a single gene, especially if you are dealing with mammals like dogs. But even without this assumption I could still claim that, the selection force, imposed by you, to favor bigger individuals, provided with enough generations, would act on genetic level that, any allele, or even allele combination, that results in a bigger phenotype would have their frequency increased in the gene pool. To address you question on how a pair of medium parents could give rise to a bigger progeny, variation is constantly emerging and disappearing in the population, and sometimes they may be hidden, so that their phenotype could only be expressed under certain conditions, plus there is always mutation acting.