evolution in populations Flashcards
give genetic factors that contribute to phenotypic variation in a species
-mutations
-random fertilisation of gametes
-independent segregation
why does natural selection occur
-disease
-predation
-competition
how does natural selection affect the gene pool over time in a population
-organisms with advantageous alleles more likely to survive and pass on their favourable alleles to offspring
-frequency of unfavourable alleles decreases
describe stabilising selection
-environmental conditions stay the same
-individuals closest to the mean are favoured so extremes are selected against and are less likely to pass on their alleles
-no evolution occurs
describe directional selection
-change in environment shifts to select for one extreme and against the other extreme
-frequency of phenotype for characteristics selected against decreases
-evolution occurs
describe disruptive selection
-change in environment shifts to favour both extremes, so mean phenotype is selected against.
-causes speciation and causes evolution
define speciation
-a population is split and different selection pressures act on each population
-causes changes in the phenotypic characteristics, and may cause for them to change to the point where they can no longer interbreed to produce fertile offspring, aka two species made
what is allopatric speciation
-speciation that occurs due to geographical separation of a population
-different environments means that different alleles are favoured
what is sympatric speciation
-speciation that occurs due to a non-physical barrier, i.e mutation
define genetic drift
-a change in the populations allele frequency that occurs due to chance rather than selection pressures
why does genetic drift affect small populations rather than large ones
-gene pool is smaller
-less alleles available and any changes to the frequency become pronounced very quickly
