population genetics Flashcards
define population genetics
the study of how allele frequencies within populations of a species change over time leading to evolution
define population
a group of organisms of the same species living in the same place at the same time
define allele frequency
the proportion of an allele within the gene pool compared to the total number of alleles for that gene
define gene pool
the total set of all the alleles for all of the genes in a population
what does the hardy weinberg principle state?
frequency of alleles in a population remains constant from generation to generation
under what 5 conditions does the hardy weinberg principle work?
- no natural selection
- no sexual selection
- no mutations
- no gene flow
- large population
define ‘species’
a group of organisms with similar physical characteristics that can interbreed to produce fertile offspring
define ‘speciation’
the evolution of a new species
define ‘isolating mechanism’
ways in which organisms become isolated from each other with no gene flow, in order to form new species
define ‘isolation’
separation of members of a species so there is no gene flow
define ‘geographical isolation’
- an isolating mechanism
- a physical barrier between members of a species, causing them to become reproductively isolated
give an example of geographical isolation
members of a population colonising a new island
define ‘allopatric speciation’
- type of speciation
- different lands
what does geographical isolation lead to?
allopatric speciation
why can an isolated species no longer produce fertile offspring?
- as phenotypes have been changing, DNA has been changing
- new alleles/genes/chromosomes
- cannot produce viable gametes through meiosis
define ‘total reproductive isolation’
reproducing isolated species together, but they will not produce fertile offspring
summarise the steps in allopatric speciation
- geographical isolation results in no gene flow between population
- random mutations occur in both populations
- different selection pressures and evolutionary forces act on each population
- accumulation of mutations and allele frequency leads to the populations becoming pheno/genotypically different
- population members are now so different they can no longer interbeed to produce fertile offspring - they are totally reproductively isolated
- allopatric speciation has occurred
define ‘sympatric speciation’
type of speciation
- same land
describe sympatric speciation
- members of a species stop breeding with each other despite still living together
summarise the steps in sympatric speciation
- random mutation leads to reproductive isolation of some of that population
- changes behaviour/ecology etc of some members - this results in no/reduced gene flow between populations
- more random mutations occur in both populations
- different selection pressures and evolutionary forces act on each population
- accumulation of mutations and change in allele frequency over many generations lead to large changes in phenotype
- members of population are so different they can no longer interbreed to produce fertile offspring (total reproductive isolation)
define ‘pre zygotic isolation’
mechanisms that prevent a zygote being created
define ‘post zygotic isolation’
mechanisms that prevent the zygote developing to full term
state the 4 pre zygotic isolation mechanisms
- temporal
- ecological
- behavioural
- mechanical
state the 3 post zygotic isolation mechanisms
- hybrid inviability
- hybrid infertility
- hybrid breakdown
define ‘temporal’ isolating mechanism
2 species mate at different times of year
define ‘ecological’ isolating mechanism
2 species occupy different habitats
define ‘behavioural’ isolating mechanism
2 species have different courtship behaviours
- eg bird song
define ‘mechanical’ isolating mechanism
physical differences prevent copulation/pollination
- eg dog breeds size
define ‘hybrid inviability’
hybrids produced but fail to develop to reproductive maturity
define ‘hybrid infertility’
hybrids fail to produce functional gametes
define ‘hybrid breakdown’
F1 hybrids are fertile but F2 generation fails to develop properly
