Diploid Selection Flashcards
What is a diploid organism?
A diploid organism has two copies of each gene, making up the majority of multicellular plants and animals.
How does reproduction differ in diploids and haploids in terms of genetic consistency?
In haploid organisms, parents “breed true,” meaning A-bearing haploid parents give rise to A-bearing offspring, whether reproducing sexually or asexually. In diploids, only asexual reproduction breeds true, while sexual reproduction introduces genetic variability (AA, Aa, aa).
What is meant by “fitness” in the context of diploid selection?
Fitness refers to the reproductive success of a genotype, denoted as WAA, WAa, or Waa for the genotypes AA, Aa, and aa, respectively. The fitness of a population is calculated by dividing the fitness of each genotype by the sum of the population.
How does fitness change over time in asexual populations?
In asexual populations, mean fitness (W) increases over time or stays the same, as selection favors more fit genotypes.
What effect does sexual reproduction have on genetic combinations formed by natural selection?
Sexual reproduction, through segregation during meiosis, breaks apart and reassorts diploid genotypes, potentially undoing genetic associations built by selection.
What are Hardy-Weinberg proportions, and under what conditions are they reached?
Hardy-Weinberg proportions are the expected genotype frequencies (p², 2pq, q²) in a population under random mating. They are reached immediately after the random union of gametes if there is no selection, migration, mutation, or genetic drift.
How does directional selection affect allele frequencies in diploid populations?
In directional selection, if WAA > WAa > Waa, allele A will rise in frequency to fixation (p = 1). If WAA < WAa < Waa, allele A will decline in frequency to loss (p = 0).
What is heterozygote advantage, and how does it affect allele frequencies?
Heterozygote advantage occurs when WAa > WAA and Waa, leading to a stable polymorphism where both alleles are maintained in the population.
What are the key assumptions of Hardy-Weinberg equilibrium?
The assumptions are random mating, no differences in fitness among genotypes, large population size, and no mutation or migration.
What is the effect of heterozygote disadvantage on allele frequencies?
In heterozygote disadvantage (WAA > WAa < Waa), either allele A or allele a will be lost depending on the initial conditions.
What is the selection coefficient, and how is it related to fitness?
The selection coefficient (s) measures the relative fitness of a genotype. For example, if Waa = 1, WAa = 1 + hs, and WAA = 1 + s, where h is the dominance coefficient and s reflects the strength of selection.
How does the dominance coefficient (h) affect allele frequency changes?
If allele A is more dominant (higher h), it rises in frequency more quickly at first but slows down as it becomes more common.
Why does selection act more slowly in diploids than in haploids?
Selection is slower in diploids because deleterious mutations can be masked in heterozygotes, whereas in haploids, every mutation is fully expressed.
What does an equilibrium point represent in population genetics?
An equilibrium is a point at which a population’s allele frequencies no longer change over time, indicating stability.
How does mutation affect allele frequency in diploid populations?
Mutations introduce new alleles, which, along with selection, genetic drift, and migration, can shift allele frequencies over time.
