Lecture 26 Flashcards
What is key to keep in mind about evolution in regards to evolution, population and individuals?
Populations evolve, individuals don’t.
What is the relationship between a population and a gene pool?
The population is a localised group of individuals of the same species. The gene pool is the total aggregate of the genes and alleles within that population at one time.
What is the Hardy-Weinberg theorem? What does it rely on?
The Hardy Weinberg theorem states that allele frequencies remain constant over time unless acted upon by evolutionary forces and that recessive alleles are not lost from populations. It requires that the population size is large, mating is random, no migration, no mutations and no natural selection.
What can we use the Hardy weinberg theorem to calculate? How?
The approximate amount of individuals with a given genotype if allele frequencies are known or vice versa. To do this we multiply all possible alleles together and make them equal one e.g for two alleles p and q, pxp =p^2, qxq = q^2, pxq = pq, qxp = pq. Hence the equation for the genotypic frequency would be p^2 + 2pq + q^2 = 1.
Note that at max you multiply two alleles together, not three at a time as individuals cannot have three alleles (unless they have three chromosomes). This can also be applied to sex chromosomes, but the relative amounts in an individual must be kept in mind
What effects cause allele frequencies to change?
non random mating (assortative mating (mating with someone similar) or inbreeding), random genetic drift, bottleneck effect, founder effect, natural selection, gene flow or migration, mutation.
What is random genetic drift?
A random change in allele frequencies due to sampling errors over generations (particularly a problem for small populations).
What is the bottleneck effect?
A large population is shrunk down to being a very small population, leaving the surviving population with altered allele frequencies.
What is the founder effect?
When a small population grows to being very large but due to the small starting alleles is relatively undiverse.
What selection types are there?
Stabilising selection: favours the average individual, reducing variation but not changing the mean.
Directional selection: selects towards an extreme value, changing the mean value towards that extreme.
Disruptive selection: favours the two extremes, leading to two new peaks in the population traits.
What is sexual selection?
Natural selection based on what individuals are bred with most rather than a survival trait.
What is frequency dependent selection?
Selection which varies based on other individuals in the population, causes natural selection to maintain an equal proportion of two types of individuals.
What is a cline?
The gradual change in allele proportions based on geographic location.
How do mutations and migrations introduce new alleles into a gene pool?
Mutations, which are slow to act and usually disadvantageous will produce new alleles which could be selected for or against into a population.
Migration of an individual from another population which successfully mates, contributing gametes to the gene pool, causes: new alleles in the gene pool, changing existing allele proportions, changes population size and makes two populations more similar.
