Populations and evolution Flashcards
What is a population
a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
What is the gene pool
the total number of genes of every individual in an interbreeding population
what is allele frequency
how often an allele occurs in a population
assumptions of hardy Weinberg principle
Mating is random
no natural selection occurs
no mutation
no genetic drift
population size is infinite
Hardy weinberg equation
p2 + 2pq + q2 =1
p is frequency of dominant allele
q is frequency of recessive allele
Sources of genetic variation
mutation - produces new alleles
random fertilisation, independent segregation + crossing over - this gives recombinant alleles
Causes of environmental variation
disease, predation + competition
what is evolution
the change in allele frequencies over time
What is directional selection
selection favours one extreme phenotype
individuals with extreme phenotype are more likely to survive and reproduce
allele frequency for extreme phenotype will increase over time
What is stabilising selection
selection favours the average phenotype/allele
individuals with average allele are more likely to survive and reproduce
allele frequency of average phenotype will increase over time and extreme allele frequency will decrease
What is disruptive selection
selection favours both extreme phenotypes but at different times due to environmental factors
individuals with average phenotype are less likely to survive and reproduce to pass on allele, so allele frequency decreases over time
whereas both extreme allele frequencies will increase over time as individuals will be more likely to survive to reproduce
define speciation
the evolution of new species from existing ones
How do new species arise by speciation
genetic differences due to selection lead to an inability of members of the population to interbreed to produce fertile offspring
What is allopatric speciation
a population becomes geographically separated
separated populations therefore reproductively isolated due to physical barrier
separate populations will have different selection pressures so they accumulate different beneficial mutations over time to help them survive
the different populations will have differential reproductive success, so allele frequencies will change differently
the different populations will become so genetically different from each other that they cannot reproduce to give fertile offspring, so are classes as different species
Describe sympatric speciation
populations become reproductively isolated due to differences in behaviour
random mutation could influence reproductive behaviour such as different fertility times or different courtship behaviour
individuals are unable to reproduce together so allele frequencies will change differently, and the DNA will become so different that individuals will not be able to produce fertile offspring
they are classed as different species
