speciation and genetic drift Flashcards
how does speciation occur
Populations become reproductively isolated (with or without physical separation)
Causes separate gene pools
Each gene pool is subjected different selection pressures leading to selection of different
features and hence different alleles;
Resulting in a different frequency of alleles;
New species arise when genetic differences mean that they are unable to interbreed to produce fertile offspring
what are the characteristics of allopatric speciation
Reproductive isolation due to geographical isolation
Different variations & selection pressures
what is seasonal isolation
different flowering or mating seasons
what is behavioural isolation
Courtship rituals
what is mechanical isolation
changes in genitalia prevent successful mating
what is hybrid infertility
odd number of chromosomes in offspring (cannot produce haploid gametes)
what can the offspring of two closely related species not do
The offspring of two closely related species are incapable of reproducing. This could be due to inheriting different numbers of chromosomes from different parents. These cannot form pairs during meiosis.
allopatric requirements
geographic isolation, mutations, different selection pressures, results in different gene pools, no interbreeding
sympatric requirements
happens in the same environment/habitat, due to morphological or behavioural isolation, resukts in different gene pools,no interbreeding
how does allopatric speciation occur
Geographical isolation/allopatric speciation
Reproductive separation/isolation
So, separate gene pools/no gene flow
Variation due to mutation
Different selection pressures
Different alleles passed on to offspring
Different allele frequency
Over time, cannot interbreed to produce fertile offspring
what happens in sympatric speciation
Mutation gives variation
Reproductive isolation;
Without geographical isolation;
Separate gene pool / no gene flow
Cannot breed/mate to produce fertile offspring
what is a gene pool
all the alleles in a population
what does genetic drift do to small populations
changes allele frequencies
what determines whether organisms survive and reproduce
Chance, rather than environmental factors determine whether organisms survive and reproduce
Thechances of an allele being lost or fixed in the population are much higher.
This is because each individual in a small population represents a larger proportion of the entire population (than in a large population).
