Underdominance is classically defined as the genetic condition where the fitness of heterozygote individuals is lower than the fitness of both of the parental homozygotes (Hartl and Clark 1989). There are two stable and one unstable equilibria in such a system with two alleles.
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What causes underdominance?
Underdominance exists in situations where the heterozygotic genotype is inferior in fitness to either the dominant or recessive homozygotic genotype. Compared to examples of overdominance in actual populations, underdominance is considered more unstable and may lead to the fixation of either allele.
Does underdominance maintain variation?
With underdominance, heterozygotes have lower fitness than both homozygotes. Underdominance does not preserve genetic variation, and one of the alleles will either be lost or spread to fixation, depending on its initial frequency.
What is the difference between underdominance and overdominance?
Underdominance is the case where heterozygotes are less fit than homozygotes: for two alleles A and B at a given locus, both AA and BB individuals are more fit than AB heterozygotes. This is the opposite of overdominance, a form of balancing selection, where heterozygotes have a higher fitness than both homozygotes.
What is negative frequency dependence?
Negative frequency-dependent selection occurs when the selective value of a variant (relative to other variants) is a function of its abundance in the population (relative to other variants) such that its relative fitness increases as the relative abundance, or frequency, of the variant decreases (Wright, 1939) (please …
What is Overdominance and example?
In overdominance, the heterozygote produced by two homozygote parents shows a phenotype that is more pronounced than that of the parents. Overdominance may also mean that the heterozygote has a higher fitness relative to the counterpart homozygotes. An example of this is a heterozygote for sickle cell anemia.
Does overdominance increase variation?
This situation, known as heterosis or overdominance, leads to the stable coexistence of both alleles in the population and hence contributes to the widespread genetic variation found in populations of most organisms.
Does overdominance maintain genetic variation?
One of the classic ways to maintain genetic variation with a population is “overdominance,” in short, a state where heterozygotes exhibit greater fitness than the homozygote genotypes.
What is balancing selection in biology?
Balancing selection occurs when multiple alleles are maintained in a population, which can result in their preservation over long evolutionary time periods. A characteristic signature of this long-term balancing selection is an excess number of intermediate frequency polymorphisms near the balanced variant.
Which factors affect natural selection?
Four conditions are needed for natural selection to occur: reproduction, heredity, variation in fitness or organisms, variation in individual characters among members of the population. If they are met, natural selection automatically results.
Can disruptive selection lead to speciation?
Disruptive selection can lead to speciation, with two or more different species forming and the middle-of-the-road individuals being wiped out. Because of this, it’s also called “diversifying selection,” and it drives evolution.
What is positive frequency dependent selection?
Positive frequency-dependent selection (FDS) is a selection regime where the fitness of a phenotype increases with its frequency, and it is thought to underlie important adaptive strategies resting on signaling and communication.
How does overdominance occur?
Overdominance. Overdominance occurs when fitness of the heterozygote is superior to that of either homozygote. The result is that both alleles are maintained in the population at an equilibrium frequency ( , read “q hat”, where q = 0) that maximizes fitness.
What causes overdominance?
1. Overdominance hypothesis: The overdominance hypothesis states that an organism that descends from parents of different genetic backgrounds will have greater resistance to a broader spectrum of potential dangers.
What is overdominance in evolution?
Overdominance is a rare condition in genetics where the phenotype of the heterozygote lies outside the phenotypical range of both homozygous parents.
What is frequency-dependent selection in biology?
Frequency-dependent selection is defined as a situation where fitness is dependent upon the frequency of a phenotype or genotype in a population. Our focus here is on negative frequency-dependent selection, whereby fitness of a phenotype or genotype increases as its frequency in a population decreases.
What is an example of frequency-dependent selection?
An example of positive frequency-dependent selection is the mimicry of the warning coloration of dangerous species of animals by other species that are harmless.
What is negative frequency-dependent selection example?
In behavioral ecology, negative frequency-dependent selection often maintains multiple behavioral strategies within a species. A classic example is the Hawk-Dove model of interactions among individuals in a population.
Who gave overdominance hypothesis?
Breeding of Vegetable, Spice and Tuber crops (2+1) The overdominance hypothesis was independently developed by Edward M. East (1908) and George Shull (1908).
How is sickle cell anemia and example of overdominance?
What are the 3 types of genotypes?
The different types of genotypes are- homozygous recessive (pp), homozygous dominant (PP), and heterozygous (Pp).
What is overdominance hypothesis of heterosis?
The overdominance hypothesis attributes the heterozygote advantage to the survival of many alleles that are recessive and harmful in homozygotes. It attributes the poor performance of inbred strains to a high percentage of these harmful recessives.
What are the three main mechanisms that can cause changes in allele frequency?
Natural selection, genetic drift, and gene flow are the mechanisms that cause changes in allele frequencies over time.
Which of the following is most likely to decrease genetic variation?
So, the correct answer is ‘Stabilising natural selection’.
Does disruptive selection increase genetic variation?
Diversifying or disruptive selection increases genetic variance when natural selection selects for two or more extreme phenotypes that each have specific advantages.