How variation developed and maintained in population?

Answer 1

Stabilizing selection for an intermediate optimum is generally considered to deplete genetic variation in quantitative traits. However, conflicting results from various types of models have been obtained. While classical analyses assuming a large number of independent additive loci with individually small effects indicated that no genetic variation is preserved under stabilizing selection, several analyses of two-locus models showed the contrary. We perform a complete analysis of a generalization of Wright's two-locus quadratic-optimum model and investigate numerically the ability of quadratic stabilizing selection to maintain genetic variation in additive quantitative traits controlled by up to five loci. A statistical approach is employed by choosing randomly 4000 parameter sets (allelic effects, recombination rates, and strength of selection) for a given number of loci. For each parameter set we iterate the recursion equations that describe the dynamics of gamete frequencies starting from 20 randomly chosen initial conditions until an equilibrium is reached, record the quantities of interest, and calculate their corresponding mean values. As the number of loci increases from two to five, the fraction of the genome expected to be polymorphic declines surprisingly rapidly, and the loci that are polymorphic increasingly are those with small effects on the trait. As a result, the genetic variance expected to be maintained under stabilizing selection decreases very rapidly with increased number of loci. The equilibrium structure expected under stabilizing selection on an additive trait differs markedly from that expected under selection with no constraints on genotypic fitness values. The expected genetic variance, the expected polymorphic fraction of the genome, as well as other quantities of interest, are only weakly dependent on the selection intensity and the level of recombination.

Answer 2

The majority of mutations are neutral with respect to the environment. This means that they are not subject to selection pressure as long as the environment stays the same. Thus neutral mutations do not tend to become either fixed in the gene pool, nor flushed from it.

Genetic variation is being generated all the time, from mutation, recombination by virtue of sexual reproduction, and by the action of viruses and transposons.

Genetic variation will also be preserved by virtue of variation within the environment. A species may inhabit a geographical range with a range of environmental conditions. Sub-species will tend to emerge, adapted to those particular environmental conditions. Partial blocks to gene flow will also help preserve distinct sub-species. A particularly clear case of this is that of ring species.

Answer 3

The process of meiosis allows for genetic variation. When the chromosomes in the parent cell separate, they tear of each other's DNA and end up with random bits of code. Also, when two gametes meet at fertilization and form a zygote they will each be carrying completely different sets of DNA so when the zygote grows it will carry DNA from each of it's two parents. Another cause for genetic variation is mutation, this is when a cell's DNA is damaged or accidentally has a different combination of acid bases. Mutation can occur by exposure to some types of radiation. When a cell is mutated it may still go through mitosis and produce more of the cells with different DNA until it is stopped by the body's immune system. The mutated cells are seen as an unknown organism and treated as a pathogen, they are eradicated. If this occurs early in the growth of the particular organism and the cell with the damaged DNA was in charge of the growth of a limb, e.g. an arm, that limb would be severely underdeveloped. The arm would be disfigured. These are only a few areas where genetic variation occurs in an organism.

This information applies only to sexual reproduction.

Answer 4

it helps the population by producing differnet kinds of people. Eg an African and chines like me is called Chafrica

Answer 5

Mutation, independent orientation of chromosomes in meiotic prophase, crossing over of genetic material in prophase of meiosis and random fertilization of and female gametes.

Answer 6

Mutation, recombination, gene flow, genetic drift and natural selection.

Answer 7

Through natural selection.