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
-individuals with average phenotype favoured and extremes selected against
-average phenotype pass on favourable alleles
-no evolution occurs
-no environmental change
describe directional selection
-one extreme phenotype favoured, all others selected against
-frequency of phenotype for characteristics selected for increases
-evolution occurs
-environmental change
describe disruptive selection
-individuals with extreme phenotype favoured, phenotypes close to mean selected against
-causes speciation and causes evolution
-change in environment
define speciation
-a population is split and different selection pressures act on each population
-causes changes in the phenotypes, 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 when 2 populations in the same area becomes reproductively isolated
define genetic drift
-changes in allele frequency in small populations due to chance
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
