Populations & evolution

• what is the hardy weinberg equation

  $p^2 +$$2pq +$$q^2 =$$1$

  $p +$$q =$$1$
• what does p stand for in the HW equation

  frequency of the dominant allele
• what does q stand for in the HW equ

  frequency of the recessive allele
• what does $p^2$ stand for in the HW equ


  frequency of homozygous dominant genotype
• what does $q^2$ stand for in the HW equ


  frequency of the homozygous recessive genotype
• what does 2pq stand for in the HW equ

  frequency of the heterozygous genotype
• Variation:

  • individuals within a population of a species may show variation in phenotype.
  • This is due to genetic and environmental factors.
  • The main source of genetic variation is mutation, random fertilisation & predation.
  • Those with advantageous phenotypes will have more reproductive success, passing on those alleles to their offspring.
  • This changes the allele frequencies in the gene pool.
• what are the three types of selection

  stabilising

  directional

  disruptive
• disruptive selection

  Is when individuals have alleles coding for either extreme phenotype are more likely to survive and pass on their alleles.

  As a result allele frequency changes & more of the extremes are present, possibly leading to speciation.
• what does the graph for disruptive selection look like?

  peaks on either extreme and a dip in the middle

  
• what does the graph for stabilising selection look like?

  Narrowing bell curve

  
• what does a directional selection graph look like?

  Graph with one extreme phenotype favored.

  
• speciation

  is the process that results in the creation of a new species
• when does speciation occur?

  When the original population of the same species becomes reproductively isolated / separated.

  This creates two populations of the same species that cannot breed together.

  This results in the accumulation of differences in the gene pools so the two populations can no longer interbreed to produce fertile offspring.
• what is allopatric speciation

  populations become separated geographically leading to reproductive isolation.
• what are the two types of reproductive isolation

  sympatric & allopatric
• what is sympatric speciation

  when populations are reproductively isolated because of differences in behaviour.

  eg. different courtship behaviours
• what is genetic drift

  a change in allele frequency within a population between generations.
• what is the mark release recapture method?

  -capture species with an appropriate technique.

  • mark them in a harmless way
  • release back into their habitat.
  • wait a week and take a second sample of the same population.
  • count how many of the second sample are marked
• whats the equation for estimating population size?

  pop size = (number caught in 1st X number caught in 2nd) / number of marked in second sample.
• what does the hardy-weinburg principle predict?

  frequency of alleles of genes in a population

  will stay the same from one generation to the next

  and no random mutations occur
• what ssumptions are made when using the hardy-weinburg principle?

  no selective advantages

  large population was used

  random mating

  no mutation

  no immegration