Topic 7B

• species: a group of organisms that can breed to produce fertile offspring
• Population: all the same species of a particular place at a particular time
• Gene Pool: The total number of alleles in a population of a species.
• Hardy Weinburg principle: the frequency of a particular allele is predicted that wont change from one generation to the next
• allele frequency: hardy Weinburg principle equation:

  P+Q=1
• genotype frequency H.W.P equation:$p^2 +$$2pq+$$q^2=$$1$

  • homo, hetero, homo
• intraspecific variation: variation within a species, due to differences in alleles
• genetic variation can occur due to:

  • crossing over & independent segregation in Meiosis
  • mutations
  • random fertilisation of gametes during sexual reproduction
• selection pressures: the forces that act on an organism to make it more or less likely to survive and reproduce
• three types of natural selection:

  • Stabilising selection
  • Directional selection
  • Disruptive selection
• Stabilising selection:

  • individuals with characteristics toward middle of range more likely to survive and reproduce- reduces range of phenotypes
• Directional selection:

  • individuals with alleles for a single extreme phenotype are more likely to survive & reproduce
• Disruptive selection:

  • individuals with the allele for extreme phenotypes are more likely to survive and reproduce
• speciation: development of new species from an existing species- whens species become reproductively isolated
• allopatric speciation:

  • Populations that are geogrsphically separated
  • different selection pressures
• Sympatric separation:

  • when random mutations occur within a population that prevent individuals that carry mutation to breed with other member of population without mutation
• reproductive isolation:

  • seasonal changes- different mating seasons
  • mechanical changes- change in shape, size or function of genitalia
  • Behavioural changes - individuals may develop different courtship rituals