[lemonhyang]

If the phenotypes are under genetic control, are they inherited through a single gene, a few genes, or many genes? how do you know?


please help.

[skimchee]

It depends on the certain trait for the phenotype. Each trait is portrayed through the genetic coding of two alleles, which could be homozygous (both dominant/recessive) or heterozygous (one dominant and one recessive)

I don't know if that helps, I explained it pretty basically.

[joogrlpekaun]

There could actually be more than two alleles for a given trait in a population, but one individual will only have two. Also, what skimchee described is only for simple Mendelian inheritance with complete dominance, which doesn't hold for all traits. Two alleles for a given Mendelian trait are not necessarily always either completely dominant or recessive in relation to each other. Don't forget about the possibility of co-dominance or incomplete dominance!

If a trait appears in a small number of discrete forms (e.g., an individual is obviously either red or blue, or obviously red or white or pink) then you know that the trait must not be controlled by a bunch of genes. That's what's going on in simple Mendelian inheritance: Mendelian traits are controlled by one gene, like a gene that makes you one color or another, one approximate height or another, produce one type of seed or another, etc. depending on the combination of alleles an individual inherits.

If, on the other hand, you examine the phenotype for a trait in a population and find that the values are all over the place along a continuum, then you know that trait in that species must be controlled by many genes that interact complexly, because you can't really point out "OK, these people are obviously tall type and these ones are obviously short type."

So for a given trait:
-If you can make obvious divisions within the population along phenotypic lines for that trait (red or white, striped or not, tall or short, wrinkled or not, whatever or whatever else), then the trait is controlled by one--or at most a very few--gene(s). If there are only two or three discrete phenotypes in the population for a trait, it's controlled by a single gene.
-If you can't make obvious divisions and the distribution for the trait among the population is continuous (the height could be anywhere from 4' to 8' with individuals all over the place in between, you measure a range of weights with individuals falling along some continuum, etc.), then that trait is controlled by many genes.

I hope that was clear and not confusing!