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​In this last module, you will see that the Hardy-Weinberg Law have a few conditions or assumptions that need to be satisfied for a population to be at equilibrium. Watch the videos to learn more about the five conditions. Notes are also available for you to refer to. Hopefully at the end of this module, you will be able to talk about the conditions in your own understanding.

Watch the following video to learn about the five major assumptions that lead to a Hardy-Weinberg equilibrium.

Can you recall how many assumptions required in order for a population to be at equilibrium?

Do you think a population would always be at equilibrium?

Evolution involves changes in the gene pool. A population in Hardy-Weinberg equilibrium shows no change. The law states that populations can keep a reservoir of variety so that the gene pool can shift if future conditions demand it. If recessive alleles continued to decrease, the population would quickly become homozygous. Genes with no current selective value will be preserved under Hardy-Weinberg circumstances.

To understand what forces drive evolutionary change, we must look at situations where the Hardy-Weinberg law does not apply. There are five of them:

1. mutation
2. gene flow
3. genetic drift
4. nonrandom mating
5. natural selection

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This video below explains the mechanisms of evolution.

The following section breaks down the mechanisms of evolution in detail.

Interbreeding is frequently limited to members of local communities. Hardy-Weinberg may be violated if the population is tiny. Chance alone may eliminate certain members in proportion to their population size. In such instances, an allele's frequency may begin to shift toward higher or lower levels. Finally, the allele may constitute 100 percent of the gene pool or, more likely, it will vanish from it. Although drift causes evolutionary change, there is no guarantee that the new population will be more fit than the old. Drift evolution is aimless and ineffective.

One of the tenets of the Hardy-Weinberg equilibrium is that population mating must be random. When people (typically females) choose their mates carefully, the gene frequencies may change. Darwin referred to this as sexual selection. Nonrandom mating appears to be rather common. It can be caused by breeding territories, courtship displays, or "pecking commands." In each scenario, certain individuals are denied the opportunity to make a proportionate contribution to the following generation.

Humans rarely mate at random, choosing phenotypes similar to their own (e.g., size, age, ethnicity). This is known as assortative mating. Marriage between relatives is a type of assortative mating. The closer the relationship, the more alleles are shared and the more inbreeding occurs. Inbreeding has the potential to affect the gene pool. This is due to the fact that it predisposes to homozygozity. Potentially detrimental recessive alleles, which are invisible in the parents, are exposed to natural selection forces in the children.

If individuals with specific genes outperform those without them in terms of producing mature kids, the frequency of those genes will rise. This is merely expressing Darwin's natural selection in terms of gene pool changes. (Darwin had no idea about genes.) Natural selection is caused by differences in mortality and/or fecundity.

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Certain genotypes fare worse than others in terms of surviving to the conclusion of their reproductive phase. The evolutionary impact of mortality selection can be seen at any time, from the development of a new zygote until the termination (if one exists) of the organism's fertile phase. Mortality selection is merely another method of expressing Darwin's fitness criteria: survival.

Certain phenotypes (therefore genotypes) may contribute disproportionately to the following generation's gene pool by producing a disproportionate number of young. This type of fecundity selection is another method of describing another fitness criterion proposed by Darwin: family size. In each of these natural selection instances, certain phenotypes are more competent than others to pass on their genes to the following generation. As a result, they are more fit according to Darwin's standards. As a result, the gene frequencies in that group gradually alter.

Watch this vidoe by Nicole Holladay on the three types of natural selection.

If the rate of mutation of B -> b (or vice versa) varies, the frequency of gene B and its allele b will not remain in Hardy-Weinberg equilibrium. This form of mutation is likely to play just a tiny influence in evolution; the rates are simply too low. However, gene (and entire genome) duplication, a type of mutation, has most likely played a significant influence in evolution. In any event, mutations are absolutely necessary for evolution because they are the only mechanism for new alleles to be formed. These supply the raw material on which natural selection can act after being shuffled in various combinations with the rest of the gene pool.

Many species are composed of limited populations, the members of which tend to breed inside the group. Each local population can establish a different gene pool from other local populations. Members of one population may, on occasion, breed with immigrants from a nearby population of the same species. This can introduce new genes or change the frequency of existing genes in the residents.
Gene flow can occur not just between subpopulations of the same species, but also between different (but still related) species in many plants and animals. This is known as hybridization. If the hybrids later reproduce with one of the parental kinds, new genes are introduced into that parent population's gene pool. This is known as introgression. It's just gene flow.