7b (populations/evolution) Flashcards
what is a species?
group of similar organisms that can reproduce to give fertile offspring
what is a population?
group of organisms of the same species living in a particular area at a particular time- so they have the potential to interbreed
what is the gene pool
the complete range of alleles present in a population
what is allele frequency?
how often an allele occurs in a population
usually given as a %
what is the hardy-weinberg principle?
what is the condition?
mathematical equation to calculate frequency of alleles in a population
assumes that the pop of dominant and recessive alleles of any gene in a pop remains same from one gen to next
what must be the case for the pop of dominant and recessive alleles of any gene in a pop to remain the same from one gen to next
no mutations occur
pop is isolated (no flow of alleles into/out of pop)
no artificial selection (all alleles are equally likely to be passed to the next generation)
large pop
mating within pop is random
when can you use hardy-weinberg equations?
when a gene has 2 alleles
what are the hardy weinberg equations?
allele frequency: p+q=1
(p- frequency of dominant allele, q- frequency of recessive allele)
genotype frequency: p2 + 2pq+ q2= 1
(assuming p is dominant and q is recessive, p2- freq. of homozygous D, 2pq- freq. of heterozygous genotype, q2- freq. of homozygous r
can you use hardy weinberg for codominant alleles?
when you dont know which is dominant or which is recessive
yes
yes (make p represent 1 allele and q the other- doesnt matter which is which as long as consistent through answer)
if you find that frequency has changed, then hardy weinberg doesnt apply to this population. why?
because hardy weinberg predicts the allele freq wont change from one gen to next
immigration, emigration, mutation, natural selection, not random mating or small population must have happened
what is variation?
what is intraspecific variation?
what can variation be caused by?
differences that exist between individuals
variation within a species (means individuals in a pop can show wide range of phenotypes)
genetic and/or environmental factors
examples of the source of genetic variation
mutation, crossing over, independent segregation, random fertilisation of gametes
what is evolution?
the frequency of an allele in a population changing over time
what are the causes of evolution?
genetic drift and natural selection
what are selection pressures?
why are there diff levels of survival
and reproductive success in a population?
pressures that affect an organisms chances of surviving eg predation, disease, competition
members of same species have diff alleles so some better adapted to selection pressures
how does evolution occur?
individuals w phenotype that increase chances of survival are more likely to survive, reproduce, pass on useful allele so greater proportion of next gen inherit the beneficial alleles.
They too more likely to survive, reproduce, pass on useful allele.
Frequency of beneficial alleles in gene pool increase from gen to gen
what is stabilising selection?
individuals with alleles for characteristics towards middle of range are more likely to survive and reproduce. occurs when environment isnt changing. it reduces range of poss phenotypes
what is directional selection?
where individuals with alleles for single extreme phenotype are more likely to survive and reproduce. could be in response to environmental change
mean stays the same
what is disruptive selection?
individuals with alleles for extreme phenotypes are more likely to reproduce, characteristics towards the middle are lost. occurs when environment favours more than 1 phenotype
what is speciation? when does it occur?
the development of a new species from an existing species
occurs when populations become reproductively isolated (changes in allele frequency which changes phenotype so can no longer interbreed to produce fertile offspring)
what is allopatric speciation?
populations that are geographically isolated (physical barrier divides a population of species so there is no gene flow between the 2 populations) experience slightly different conditions eg climate. also experience diff selection pressures so diff changes in allele frequency occur
diff alleles more advantageous in diff pops so natural selection occurs. directional selection acts on alleles increasing their freq.
allele freq also changes as mutations occur independently in each pop
genetic drift may also affect allele freq
overtime, this leads to speciation. changes in allele freq lead to diffs in gene pools. eventually, theyll change so much that they become reproductively isolated
what is sympatric speciation?
when random mutations within a population prevents individuals that carry the mutation from breeding with other members of the pop that dont have the mutation
very rare as difficult for a section of a pop to become reproductively isolated without a geographical barrier
what are the mechanisms for reproductive isolation?
seasonal changes- individuals developing diff mating seasons- arent reproductively active at same time
mechanical changes- changes in shape, size, functional of genitalia
behavioural changes- group of individuals developing courtship rituals that arent attractive to rest of species
gametic- gametes cant fit/fuse together
how does evolution occur through genetic drift?
chance dictates what alleles are passed on instead of environmental factors
individuals within a pop show variation in genotypes
by chance one of the alleles is passed on to more than another so no of individuals with that allele increases
passed on again and again- leads to evolution
does genetic drift have a greater effect on smaller or larger populations? why?
smaller populations
in larger populations, chance factors tend to even out across whole population and have less of an effect
does hardy weinberg apply to populations affected by genetic drift?
no because genetic drift affects small populations but hardy weinberg only applies to large populations
