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Allele Frequencies

The Hardy-Weinberg equilibrium principle is summarized as both allele and genotype frequencies within a population remain continuous between generation to generation unless specific disturbing influences are introduced. Genetic equilibrium is an ideal state that provides a baseline to measure genetic variation against. The Hardy-Weinberg equation sums up all of the genotypic frequencies within a population. The equation can be used to calculate the frequency of alleles in a gene pool, if the frequencies of all genotypes are given. The equation is p2 + 2pq + q2 = 1. Where the frequency of the dominant X allele = p. The frequency of the homozygous dominant XX genotype is (p)(p), or p2. The expression 2pq is the frequency of the heterozygous genotype Xx. The expression q2 represents the frequency of the homozygous recessive xx genotype. The total frequency =1. The Hardy-Weinberg equilibrium equation only works if the population meets these five assumptions.

1. Random mating, - All allele and genotype frequencies in a population have equal opportunity to propitiate.

2. There is no mutations, - No changes in the DNA sequence creating new allele, which would lead to genetic deviation from the parent population. Mutations can be caused by copying errors in the genetic material during cell division, and is almost always harmful to the organism. Mutations create variation within the gene pool and are the source of all heritable variations. Less favorable mutations can be reduced in frequency through natural selection, while more favorable mutations may accumulate and result in adaptive evolutionary changes.

3. There is a large population size, - this minimizes random sampling errors. With a large population size the effect of change is minor to the total population. The more individuals in the habitat, the lower the ratio of change in the population become.

4. There is no gene flow, - no outside influences diluting the genetic purity. Migration brings two or more populations together allowing their genetic variations to enter the other's gene pool. The allele frequencies will become more homogeneous through the combination of the two individual populations. Models for migration inherently include nonrandom mating invalidating the principles of Hardy-Weinberg.

Disasters that greatly reduces an existing population” numbers may force the remaining inhabitants to experience genetic drift, the change in the relative frequency of alleles that occurs in a population due to random sampling and chance, certain alleles may no longer be present, and others may be overrepresented in the new populations'

gene pool. After genetic drift, the gene frequency of the reduced population will no longer be representative of the original population.

5. There is no natural selection, - no picking the best of the best, this filters out the less desirable genetic traits in the overall population. Natural selection can lead to allele-frequency changes in a population Natural selection is the process by which the heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over subsequent generations. The natural genetic variation within a population means that some individuals will survive and reproduce more successfully than others in their current environment.

Hardy Weinberg equilibrium is unobtainable outside the lab conditions. In nature there are always one or more selective pressures affecting a species. Genetic equilibrium provides a baseline to measure genetic change against. From the Hardy-Weinberg equilibrium equation, we can predict useful but difficult-to-measure facts about a population.

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