20.5 Evolution Flashcards
Gene pool
Sum total of all the genes in a population at any given time
Allele frequency
Relative frequency of a particular allele in a population
Hardy Weinberg principle
In a stable population with no disturbing factors, allele frequencies will remain constant from one generation to the next and there will be no evolution
Hardy Weinberg Formula
p2 + 2pq + q2 = 1
p2 = frequency of homozygous dominant
2pq = frequency of heterozygous
q2 = frequency of homozygous recessive
Factors affecting evolution
Mutations - causes different alleles
Sexual selection - increase in frequency of alleles that code for characteristics that improve mating success
Gene flow between populations
Genetic drift in small populations - change in allele frequency due to mutations
Natural selection - more individuals with advantageous characteristics
Factors affecting size of a population
Density dependent - depends on population size eg - competition and predation
Density independent - affects populations of all sizes in the same way eg - natural disasters and seasonal change
Genetic bottleneck
Large reduction in population size that lasts for at least one generation - gene pool and genetic diversity are greatly reduced
Positive aspect of genetic bottlenecking
Beneficial mutations have a much greater impact and lead to quicker development of a new species
Founder effect
Genetic drift causes a smaller population with smaller gene pools and low genetic variation
Stabilising selection
When the norm is selected for and the extremes are selected against
Reduced frequency of alleles at the extremes
Directional selection
Occurs when the most common phenotype is no longer the most advantageous
Allele frequency shifts towards the extremes
Disruptive selection
Extremes are selected for and norm is selected against
