How can we determine what effect mutation has on the phenotype of a population?

surely that can only be seen over millions of years?

Natural selection does not know what is best for the genome; there is no standard for what is “best.” Natural selection may affect mutations which have a phenotypic impact – and this does include physiological and developmental genes (because they affect phenotype) – but there is a threshold strength below which a mutation does so little to the phenotype that natural selection cannot even see it.

What does this mean? It means that if you are born with no appendages natural selection will very easily trim you from the population. But if you are born and you are .003 inches taller than your brother, natural selection does not see any difference. In fact, simply due to genetic recombination, he might inherit a gene or two from your parents that gives him a tiny advantage over you, and even if your height was even more superior (or inferior) to his, it would not have a net impact strong enough to make natural selection see either of you differently.

Many, many mutations have a very small phenotypic effect. But many of them occur, and many of them are missed by natural selection. And in the long run this means that a whole lot of genome randomization occurs.

Have you ever erased just one letter from a word in a poem (or replaced it with a random one)? Then just another couple letters? Then a couple more? It’s not that big of a deal, because if you are used to reading the poem you can still see the words for a long time despite the few missing letters.

But eventually the “environment” (in this case the person reading the poem) will change, and suddenly all those missing letters will make it impossible to understand. And thus is the story of genetic entropy.

Try this website:

www.bookrags.com/Genotype-phenotype_distinction