How does natural selection affect polygenic traits?

Answer 1

Polygenic traits occur because of genes and environment. There are usually two or more genes involved in these traits. It also takes into consideration where the organism lives, for example the fact that some hotter areas have a history of people with darker skin tones.

Answer 2

Traits and selctive breeding are related in that during selective breeding you have to choose from traits form you and your partner. the traits you have may be passes through selctive breeding.

Answer 3

Without going into a long and technical discussion of the population genetics of polygenic vs. simplex traits, one could simply say that they're affected in much the same way: the frequency of some traits is reduced, while the frequency of other traits is increased, regardless of whether they're polygenic in nature or simplex.

There is a noteworthy difference, however: simplex traits may be eradicated from the population gene pool entirely, if they have no essential secondary function. But in most complex traits it's much more likely that one or more of the genes involved has some secondary function, or that the complex is interlinked in such a way that removal of a part or the whole would leave a disabled organism. Height, for instance, can be considered a trait, but is really a variation in the way a developing organism, under influence of many genetic factors, grows. You cannot eliminate "short" from the population without affecting the genes that make growth possible at all.

Another complication is that polygenic traits usually come in a spectrum of variations. For instance, one could regard height as a single trait with many possible values, ranging from "short" to "long". In such cases, one could distinguish three ways that natural selection might act on the trait:

Directional selection occurs when phenotypes at one end of the spectrum lead to greater survival and/or reproduction. Stabilizing selection occurs when phenotypes in the middle range confer greater survival/reproduction, while phenotypes at both extremes lead to decreased fitness. Disruptive selection is the least common of the three types and occurs when phenotypes at both endsof the spectrum lead to greater survival and reproduction, while phenotypes in the mid range are a disadvantage.

A single additional observation may be of interest: it's possible that natural selection favours a polygenic trait in which one of the genetic components has a detrimental impact - the benefits of the complex entire may outweigh the detrimental impact of the single component gene.

Answer 4

It could give the offspring a trait that the scientist doing the selective breeding dont want the offspring to have.