18.1population genetics Flashcards
gene pool
all of the alleles of all the genes of all the individuals in a population at a given time
allelic frequency
the number of times an allele occurs within the gene pool
hardy weinberg principle
the proportion of dominant and recessive alleles of any gene in a population remains constant over generations
hardy weinberg conditions
- no mutations
- population is isolated
- no selection occurs
- population is large
- mating in the population is random
Hardy weinberg phenotype equations
p+q=1
Genetic variation
- mutations
- meiosis
- random fertilisation of gametes
selection pressure
environmental factors that limit population
Natural selection factors
- organisms produce more offspring than can be supported by available food, light and space
- genetic variety within populations of all species
- variety of phenotypes that selection operated against
Stabilising selection
- occurs in unchanging environment
- selection against extreme phenotypes
- standard deviation is reduced
- preserves average phenotype
Directional selection
-occurs in changing phenotype
-favours one extreme phenotype so mean shifts towards
-selection against mean phenotype
Disruptive selection
-occurs in changing environment
-favours both mean phenotypes
-selection against mean phenotype
Species
Able to breed to produce healthy, fertile offspring
Speciation
evolution of new species from existing ones
allopatric speciation
different species form from different populatins in different areas
sympatric speciation
different species form from the same population in the same area
sympatric speciation explanation
- occurs in the same habitat
- mutation causes variation in behaviour/ ecology/temporal
- reproductive isolation
- different favourable alleles are passed on
- change in allele frequency
- populations can’t interbreed to produce fertile offspring
allopatric speciation explanantion
- geographical isolation occurs
- different environmental conditions cause different selection pressures
- random mutations cause variation
- favourable alleles passed on to offspring
- change in allele frequency
behavioural
different courtship displays
temporal
different breeding seasons
different feeding times
mechanical
mismatch in reproductive parts
gamete incompatibility
allele frequency
P^2 + 2pq + q^2 = 1
genetic drift
change in frequency of existing gene variant in population due to random chance
intra
within same species
inter
across different species
