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Population genetics is the study of genetic variation within and among populations and the evolutionary factors that explain this variation. Its foundation is the Hardy - Weinberg principle, which states that in any population allele and genotype frequencies remain constant as long as the population size is large, random mating, no mutation, no natural selection and no gene flow. When these assumptions are violated, allele frequencies and genotype frequencies may change from one generation to the next.

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1) To learn about human migration and history
2) To identify and localize disease genes
3) To identify difference in linkage disequilibrium for fine mapping
4) To avoid false positive data due to population stratification (age, lifestyle, nutrition, genetics)
5) Mapping of disease
6) Signature of natural selection

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Genetic variation refers to diversity in gene frequencies. Genetic variation is the difference in DNA among individuals or the differences between populations. There are multiple sources of genetic variation, including mutation and genetic recombination. Mutation is the ultimate source of genetic variation which is amplified by combination during sexual reproduction.

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Genetic variation in a group of organisms enables some organisms to survive better than others in the environment in which they live in. Organisms of even a small population can differ strikingly in terms of how well suited they are for life in a certain environment.
For example, moths of the same species with different color wings. Moths with wings similar to the color of tree bark are better able to camouflage themselves than moths of a different color. As a result, the tree-colored moths are more likely to survive, reproduce, and pass on their genes. This process is known as natural selection, and is one of the main forces that drives evolution.

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Types of Selections Which Alters the Genetic Variance of A Population

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Types of Selections Which Alters the Genetic Variance of A Population

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1. Stabilizing selection
Causes a decrease in a population‘s genetic variance. Occurs when natural selection favors an average phenotype and selects against extreme variations.

2. Directional selection
A population’s genetic variance shifts toward a new phenotype when exposed to environmental changes. Selects for phenotypes at one end of the spectrum of existing variation.

3. Diversifying selection
Causes an increase in genetic variance when natural selection selects for two or more extreme phenotypes that each have specific advantages. Average or intermediate phenotypes are less fit than either extreme phenotype and are unlikely to feature prominently in a population.

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Natural selection is the process in which populations of living organisms adapt and change. The variations of individuals in a population shows that some individuals have traits better suited to the environment than others. Individuals with adaptive traits are more likely to survive and reproduce allowing these traits to be passed on to their offspring.  Thus, these advantageous traits become more common in the population over time. Through natural selection, favorable traits are transmitted through generations. Natural selection can also lead to speciation, where one species gives rise to a new and distinctly different species. It is one of the processes that drives evolution and helps to explain the diversity of life on Earth.

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Also known as "Darwin's Finches", 14 different species of finches discovered by Charles Darwin at the Galapagos Islands became the foundation of evolution. It was found that the birds of the different species had different beaks. This is due to adaptation to the type of food that were eaten in order to fill different niches of the Galapagos Islands. Isolation on the islands over long periods of time caused speciation

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Polymorphism involves one of two or more variants of a particular DNA sequence. The most common type involves variation at a single base pair. Polymorphisms can also be much larger in size and involve long stretches of DNA.

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1) Classical
2) Isozyme
3) Restriction Fragment Length Polymorphism (RFLP)
4) Amplified Fragment Length Polymorphism (AFLP)
5) Random Amplified Polymorphic DNA (RAPD)
6) Microsatellites
7) Single-Nucleotide Polymorphism (SNP)