Human genetic variation is the genetic differences both within and among populations. There may be multiple variants of any given gene in the human population (genes), leading to polymorphism. Many genes are not polymorphic, meaning that only a single allele is present in the population: the gene is then said to be fixed.
No two humans are genetically identical. Even monozygotic twins, who develop from one zygote, have infrequent genetic differences due to mutations occurring during development and gene copy number variation. Differences between individuals, even closely related individuals, are the key to techniques such as genetic fingerprinting. Alleles occur at different frequencies in different human populations, with populations that are more geographically and ancestrally remote tending to differ more.
Causes of differences between individuals include the exchange of genes during meiosis and various mutational events. There are at least two reasons why genetic variation exists between populations. Natural selection may confer an adaptive advantage to individuals in a specific environment if an allele provides a competitive advantage. Alleles under selection are likely to occur only in those geographic regions where they confer an advantage. The second main cause of genetic variation is due to the high degree of neutrality of most mutations. Most mutations do not appear to have any selective effect one way or the other on the organism. The main cause is genetic drift, this is the effect of random changes in the gene pool. In humans, founder effect and past small population size (increasing the likelihood of genetic drift) may have had an important influence in neutral differences between populations. The theory that humans recently migrated out of Africa supports this.
The study of human genetic variation has both evolutionary significance and medical applications. The study can help scientists understand ancient human population migrations as well as how different human groups are biologically related to one another. From a medical perspective the study of human genetic variation may be important because some disease causing alleles occur at a greater frequency in people from specific geographic regions. New findings prove that there are, on average, 60 new mutations in each human from their parents. Many genes that may have originally aided people now plague them in modern times, although they're not a mutation by the traditional definition. It is suspected that genes that once allowed people to be more efficient in processing food are now the same ones that lead those people to be susceptible to obesity and diabetes.
Read more about Human Genetic Variation: Genetic Variation, Measures of Variation, History and Geographic Distribution, Categorization of The World Population, Health, Genome Projects
Famous quotes containing the words human and/or genetic:
“If there is technological advance without social advance, there is, almost automatically, an increase in human misery, in impoverishment.”
—Michael Harrington (19281989)
“We cannot think of a legitimate argument why ... whites and blacks need be affected by the knowledge that an aggregate difference in measured intelligence is genetic instead of environmental.... Given a chance, each clan ... will encounter the world with confidence in its own worth and, most importantly, will be unconcerned about comparing its accomplishments line-by-line with those of any other clan. This is wise ethnocentricism.”
—Richard Herrnstein (19301994)