Selective breeding

[Katchit]

Hello; i am new to the forum.

I would like to ask you about selective breeding and the chances of producing a Taurus (bull) that displayed favourable traits and phenotypes of 2 selectively-picked cattle; thus to produce a better offspring as a result.

Taurus have 30 chromosome pairs; so what are the potential outcomes of the breeding?

How do favourable phenotypes become dominant? is that just a result of the phenotype being heterozygous dominant?

Am i correct in thinking that it is important to keep as many different phenotype combinations in genes as possible; as this allows for diversity within a species?!? if the potential phenotypic combinations were reduced; would this mean that the species would begin to look more and more alike with continued breeding?

Thank you for your time and help; much appreciated.

[4N6addict]

Hello!

Phenotypes do not tell us which genotype the cattle possesses, so you would have a bit of trial and error involved in the breeding unless you have a pedigree.

There is no way to make a particular trait dominant, it either is or it isn't. The good news is, if you have a recessive trait that you want passed on, you are guaranteed that trait by breeding two specimens who already exhibit it.

If you are dealing with a dominant trait, you still want that trait to be "pure". Meaning, in most circumstances you would want the animal to have both alleles for the trait. This is for a couple reasons:
1) It ensures the animal will pass that trait on to offspring.
2) Some traits which are dominant have a "range" within which they can be expressed. So if an animal has one allele for the dominant trait and one for the recessive (heterozygosity), there may still be a bit of "co-dominance" for the trait and it may not be expressed as fully as if you have two alleles for the dominant trait (homozygosity).

So either way (dominant or recessive) the goal is to ensure the animal has both alleles for a given trait. The only way to do this, short of sequencing their DNA, is to continue breeding animals expressing that trait until you no longer see any other traits being expressed.

As far as keeping different combinations in genes, it really depends on what your purpose is. With extensive inbreeding, you can start to see higher mutation rates (which can result in birth defects, etc.). But if your goal is to create the ideal bull, I don't know how much that really matters. Additionally, I think cattle as a species are more resistant to these defects than humans are (or they just aren't as evident, it can be hard to tell if your cow is not very intelligent). With inbreeding, you do reduce the genotypic diversity, which in turn reduces phenotypic diversity, so yes, the cattle will begin to express similar traits.

Hope some of that helped!