Genetic variations in the human genome can take many forms, including single nucleotide changes or substitutions; tandem repeats; insertions and deletions (indels); additions or deletions that change the copies number of a larger segment of DNA sequence; that is, copy number variations (CNVs); other chromosomal
Genetic variation is increased by meiosisRecombination or crossing over occurs during prophase I. Homologous chromosomes – 1 inherited from each parent – pair along their lengths, gene by gene. Independent assortment is the process where the chromosomes move randomly to separate poles during meiosis.
Mutations, the changes in the sequences of genes in DNA, are one source of genetic variation. Another source is gene flow, or the movement of genes between different groups of organisms. Finally, genetic variation can be a result of sexual reproduction, which leads to the creation of new combinations of genes.
Genetic drift can result in the loss of rare alleles, and can decrease the size of the gene pool. Genetic drift can also cause a new population to be genetically distinct from its original population, which has led to the hypothesis that genetic drift plays a role in the evolution of new species.
The bottleneck effect is an extreme example of genetic drift that happens when the size of a population is severely reduced. Events like natural disasters (earthquakes, floods, fires) can decimate a population, killing most individuals and leaving behind a small, random assortment of survivors.
variation. / (ˌv??r?ˈe???n) / noun. the act, process, condition, or result of changing or varying; diversity. an instance of varying or the amount, rate, or degree of such change.
Why is variation important within a population? With variation, individuals will be different from one another and those differences allow some to survive better than others. With variation, selection has something to work on.
Mutations are the original source of genetic variation. A mutation is a permanent alteration to a DNA sequence.
Common human variations
| Type of Variation | Example |
|---|
| Skin Color | Human skin color Albinism |
| Eye Color | Eye color Martin scale |
| Hair Color | Human hair color Hair coloring |
| Hair Quantity | Hair loss Hirsutism |
Examples of types of variation include direct, inverse, joint, and combined variation.
Variation in a characteristic that is a result of genetic information from the parents is called inherited variation . This is because they get half of their DNA and inherited features from each parent. Each egg cell and each sperm cell contains half of the genetic information needed for an individual.
The genetic variation on which natural selection acts may occur randomly, but natural selection itself is not random at all. The survival and reproductive success of an individual is directly related to the ways its inherited traits function in the context of its local environment.
Without genetic variation, a population cannot evolve in response to changing environmental variables and, as a result, may face an increased risk of extinction. For example, if a population is exposed to a new disease, selection will act on genes for resistance to the disease if they exist in the population.
Whether eyes are blue or brown, eye color is determined by genetic traits handed down to children from their parents. A parent's genetic makeup determines the amount of pigment, or melanin, in the iris of the his or her child's eye. With high levels of brown melanin, the eyes look brown.
Sexual reproduction can increase genetic variation but reduce species diversity. Melian, "is that if sex increases genetic variation and speeds up evolution, then ecosystems will have a higher number of species that reproduce sexually.
We have seen that meiosis creates variation three ways: crossing over, mutations caused during crossing over, and independent assortment.
