Mutations Flashcards
What is genetic variance in fitness and why is it important for evolution?
Genetic variance in fitness refers to differences in the average fitness of alleles at a locus. It is the fundamental factor upon which evolution acts, as it provides the variation needed for selection to drive evolutionary change.
In a one-locus model with haploid selection, what is the outcome in terms of genetic variation?
In a one-locus haploid selection model, either the allele A or a becomes fixed in the population, leading to no genetic variation.
How does heterozygote advantage in a diploid model maintain genetic variation?
Heterozygote advantage leads to a polymorphic equilibrium, where both alleles A and a have equal fitness on average, maintaining genetic variation in the population.
What are the 4 primary types of mutations, and how do they differ?
Point mutations: Changes in a single nucleotide; most mutations fall into this category.
Transition mutations: Occur between similar nucleotide types (purine to purine or pyrimidine to pyrimidine).
Structural mutations: Larger changes, including deletions, duplications, inversions, and chromosome fusions or fissions.
Wide-scale genomic mutations: Entire genome duplications, leading to polyploidization.
What is the ultimate source of novel genetic variation?
Mutation is the ultimate source of novel genetic variation, providing new alleles for selection to act upon.
How does the mutation rate vary among organisms and genes?
Mutation rates vary widely. In eukaryotes, point mutations occur at a rate of approximately 10^-8 to 10^-10 per base pair per generation, and 10^-5 to 10^-7 per gene per generation. Rates can also differ among genes and even among alleles of the same gene.
Why are forward mutations typically more common than back mutations?
Forward mutations, which disrupt wildtype function, often occur at higher rates than back mutations, which restore wildtype function. This is because there are usually more ways to disrupt a gene than to repair it.
What is the relationship between mutation and selection in evolutionary processes?
While selection removes deleterious alleles that reduce fitness, mutation continually reintroduces them, leading to a mutation-selection balance in populations over time.
What is the mutation-selection balance, and why does it occur?
The mutation-selection balance occurs when the rate of new deleterious mutations introduced into a population equals the rate at which selection removes them. This balance allows deleterious alleles to persist in the population despite their negative effects.
What happens to mean fitness over time in a population with mutation and selection acting together?
Even in populations that start with no mutations, mean fitness declines over evolutionary time due to the continuous introduction of deleterious mutations. This reduction in fitness is referred to as the “mutation load.”
What is “mutation load,” and how does it impact a population’s fitness?
Mutation load refers to the reduction in a population’s mean fitness due to the accumulation of deleterious mutations. It depends primarily on the mutation rate and can result in a population where a certain fraction of individuals die due to the presence of harmful mutations.
How does the mutation load differ between haploids and diploids?
In diploids, the mutation load is generally greater (2u) because mutations can affect both heterozygotes and homozygotes. In haploids, it is lower, as only one copy of each gene is present.
Why do recessive mutations reach higher frequencies than dominant ones in diploids?
Recessive mutations are only expressed in homozygous individuals, allowing them to persist at higher frequencies in the population compared to dominant mutations, which are exposed to selection in heterozygotes.
How do mutation rates impact the prevalence of disease-causing alleles in a population?
Diseases caused by mutations are found at an equilibrium between mutation introducing new disease alleles and selection removing them. Higher mutation rates lead to a greater prevalence of these alleles.
What is the general mutation rate per base pair per generation in eukaryotes?
The mutation rate in eukaryotes is approximately 10^-8 to 10^-10 per base pair per generation.
