Natural selection #9 Flashcards
What is natural selection?
Natural selection is a mechanism of evolution by which certain traits become more or less common in a population over time, depending on how they affect the reproductive success of individuals. It is based on the idea that individuals with traits that are better adapted to their environment are more likely to survive and reproduce, passing those traits on to their offspring.
What is the genetic theory of natural selection?
The genetic theory of natural selection proposes that a consistent difference in fitness among different classes of biological entities, such as individuals or genes, leads to evolutionary change. Fitness is defined as the number of offspring an individual produces that survive to reproduce themselves, and selection can affect fitness at different stages of the life cycle.
What are the conditions necessary for evolution by natural selection to occur?
Evolution by natural selection occurs when there is a correlation between phenotype and fitness, meaning that individuals with certain traits have higher fitness than others. Additionally, there must be variation in phenotype that is heritable, meaning that offspring resemble their parents in terms of their traits.
What is the difference between evolution and no evolution in the context of natural selection?
In the absence of natural selection, the mean value of offspring will be the same as the mean value of all parents. However, in the presence of natural selection, only the largest individuals survive and reproduce, so the mean trait in offspring will be greater than the mean of all parents before selection.
What is fitness and how is it related to selection?
Fitness is the number of offspring an individual produces that survive to reproduce themselves. It is the currency of selection, meaning that individuals with higher fitness are more likely to pass their traits on to the next generation. Selection can act on fitness at different stages of the life cycle.
What is relative fitness and how is it calculated?
Relative fitness is the fitness of a particular allele, genotype, or phenotype relative to the most fit genotype in the population, which is assigned a relative fitness of 1. It is calculated by dividing the fitness of the genotype of interest by the fitness of the most fit genotype.
How does the strength of selection impact the rate of evolution?
The rate of evolution is proportional to the strength of selection and the amount of genetic variation. Stronger selection leads to faster evolution. The rate of adaptation depends on the relative fitness advantage of the favored allele, which is measured by the selection coefficient.
What is positive selection and what is an example of it?
Positive selection occurs when an allele with higher fitness increases in frequency. An example of positive selection is the evolution of lactase persistence in humans, which is caused by a mutation that allows adults to digest lactose in milk. In populations where cattle were domesticated, natural selection favored individuals with the mutation, leading to its high frequency today.
What is negative selection and how does it impact genetic variation?
Negative selection, also known as purifying selection, reduces genetic variation by removing deleterious alleles from a population. It occurs when individuals with certain traits have lower fitness than others. The selection coefficient is negative and the change in allele frequency is also negative.
What is mutation-selection balance and how does it impact genetic variation?
Mutation-selection balance occurs when the rate of mutation introducing deleterious alleles into a population is balanced by the rate of selection removing those alleles. In the case of nearly or completely recessive mutations
