4.4 genetic diversity and adaptation

• what is genetic diversity

  number of different alleles of genes in a population
• what are alleles and how do they arise?

  variations of a particular gene (same locus) → different DNA base sequence

  arise by mutation
• what is a population

  a group of interbreeding individuals of the same species
• the importance of genetic diversity

  enables natural selection to occur

  in certain environments, a new allele of a gene might benefit its possessor

  by resulting in a change in the polypeptide (protein) coded for that gene positively changes its properties

  giving possessor a selective advantage (increased chances of survival and reproductive success)
• what is evolution

  change in allele frequency (how common an allele is) over many generations in a population

  occurring through the process of natural selection

  adaptation and selection are major factors in evolution and contribute to the diversity of living organisms
• explain the principles of natural selection in the evolution of populations

  mutation -> random gene mutations can result in [named] new alleles of a gene

  advantage -> in certain [named] environments, the new allele might benefit its possessor [explain why] → organism has a selective advantage

  reproductive success -> possessors are more likely to survive and have increased reproductive success

  inheritance -> advantageous allele is inherited by members of the next generation (offspring)

  allele frequency -> over many generations, [named] allele increases in frequency in the population
• naturtal selection

  natural selection results in species that are better adapted to their environment
• anatomical adaptations

  structural / physical features that increase chance of survival
• physiological adaptations

  processes / chemical reactions that increase chance of survival
• behavioural adaptations

  ways in which an organism acts that increase chance of survival
• directional selection

  example -> antibiotic resistance in bacteria

  organisms with an extreme variation of a trait have a selective advantage

  eg bacteria with high level of resistance to a particular antibiotic

  change in environment -> yes, usually

  eg antibiotic introduced

  effect of potation over many generations ->

  increased frequency of organisms with / alleles for extreme trait

  normal distribution curve shifts towards extreme trait
• stabilising selection

  example -> human birth weight

  eg organisms with an average / modal variation of a trait have a selective advantage

  eg babies with an average weight

  change in environment -> no, usually stable

  effect on population over many generations ->

  increased frequency of organisms with / alleles for average trait

  normal distribution curve similar, less variation around the mean