genetic diversity and selection

• allele

  one of a number of alternative forms of a gene. For example, the gene for the shape of pea seeds

  has two alleles: one for ‘round’ and one for ‘wrinkled’.
• antibiotic resistance

  the development in microorganisms of mechanisms that prevent antibiotics from killing them.
• directional selection

  when selection pressures on a population cause more individuals at one extreme of the phenotype to survive and reproduce.
• founder effect

  the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.
• gene mutation

  a change to one or more nucleotide bases in DNA resulting in a change in genotype which may be inherited.
• genetic bottleneck

  a sharp reduction in the size of a population due to environmental events or human activities often resulting in a reduction in genetic diversity.
• genetic diversity

  the number of different alleles present in a population.
• mutation

  a sudden change in the amount or the arrangement of the genetic material in the cell.
• pasmid

  a small circular piece of DNA found in bacterial cells.
• population

  a group of individuals of the same species that occupy the same habitat at the same time.
• selection

  process that results in the best-adapted individuals in a population surviving to breed and so pass their favourable alleles to the next generation.
• selection pressure

  the environmental force altering the frequency of alleles in a population.
• selective breeding

  breeding of organisms by human selection of parents/gametes in order to perpetuate certain characteristics and/or to eliminate others.
• stabilising selection

  when selection pressures on a population cause more individuals near the average phenotype to survive and reproduce.