population and evolution Flashcards
what is allelic frequancy
the number of times an allele occurs within a gene pool
what are the assumptions of the hardy weinburg principle
- no muttations
- the population is isolated and no flow of alleles into or out of the population
- no selection
- population is large
- mating in the population is random
allele frequancy equation
P+Q = 1
genotype frequancy equation
P^2 + 2PQ + Q^2 = 1
two causes of genetic varriation
crossing over / independanct segregation
random fertilisation
do environmental factors have influence on genetic varritaion
no little influence
factors influencing natural selection
- organisums produce more offspring than can be supported by the environment
- there is genetic varriation within the popultaion
- subsequently there is phenotypic varitaion
- predation , disease and competition results in differentail survival and reproduction of individuals
how does reproductive success affect allele frequancy
organisums produce more offspring than the environment can support
population remains relatively constant because intraspesific competition
random mutations of alleles within the gene pool means some are more likely to survive than others and reproduce
new alleles with the selective advantage will be passed on so these individuals will also reproduce and advantagous alleles frequancy in the population increases
what is directional selection
when a population moves from one phenotype to another
chance mutation in a gene produces a new allele
( antibiotics )
what is stabalising selection
a reduction of varriation about an optimum model value
what is disruptive slection
favours extreme phenotypes at the expense of intermediate phenotypes
what is speciation
the individuals of one species can freely interbreed as they share the same area
their habitats becomes geographically isolated
abiotic and biotic conditions become different and selectional pressures are differnent
as always there is genetic varriation caused by gene mutation
different advantagous phenotypes are selected to survive
organisums survive and re produce
in each isolated population the frequancy of alleles for advantagous phenotypes increase and are passed on
no interbreeding between populations and there is no gene flow between gene pools
differences in gene pools become so big that they cannot interbreed to produce fertile offspring
what is genetic drift
change of alleles over time
it occurs in small poulations because chance has a greater role to play in which alleles are passed on
what is a genetic bottleneck
a sharp reduction in population size , random alleles survive and frequancy changes
what is the founder effect
population is decended from a small number of colonising ancestors - low genetic varriation
what is geographical isolation
two populations become seperated due toa physical barrier
what is allopatric speciation
when two populations have becoe georgraphically sperated due to a physical barrier
different environmental conditions means natural selection influences the population differently cauing local adaptations
what is sympatric speciation
occurs in the same geographical area but different populations are reproductively isolated due to behavioral differences
