• Organisms that belong to the?same?species?share the?same characteristics?and are able to produce?fertile offspring
• Reproductive isolation occurs when changes in the?alleles?and?phenotypes?of some individuals in a population?prevent?them from successfully?breeding?with other individuals in the population that don't have these changed alleles or phenotypes
• Examples of allele or phenotype changes that can lead to reproductive isolation include:
  • Seasonal?changes?- some individuals in a population may develop different?mating?or?flowering?seasons (becoming sexually active at different times of the year) to the rest of the population (i.e their?reproductive timings?no longer match up)
  • Mechanical changes?- some individuals in a population may develop changes in their?genitalia?that prevent them from?mating?successfully with individuals of the opposite sex (i.e. their?reproductive body parts?no longer match up)
  • Behavioural changes?- some individuals in a population may develop changes in their?courtship behaviours, meaning they can no longer?attract?individuals of the opposite sex for?mating?(i.e. their methods of attracting a mate are no longer effective)
• These changes could be brought about due to?geographical barriers?isolating populations or?random mutations?producing new, different alleles in a population

Speciation

• Speciation can occur when populations of a species become?separated?from each other by?geographical?barriers
  • The barrier could be?natural?like a body of water, or a mountain range
  • It can also be?man-made, like a motorway
• This creates two populations of the same species who are?reproductively isolated?from each other, and as a result,?no genetic exchange?can occur between them
• If there are sufficient?selection pressures?acting to change the?gene pools?(and allele frequencies) within both populations then eventually these populations will?diverge?and form?separate species
  • The changes in the alleles/genes of each population will affect the?phenotypes?present in both populations
  • Random mutations?within each population will also change allele frequencies in each
  • Over time, the two populations may begin to?differ?physiologically, behaviourally and anatomically (structurally)

Speciation occurring due to geographical isolation of two populations of the same species