3.4.4 Genetic diversity and adaption

• Genetic diversity 


  All the different alleles in a population
• How can genetic diversity arise?

  Cross over (meiosis 1)

  Independent segregation (meiosis 1 + 2)

  random gamete combination

  gene mutation

  Non-disjunction (meiosis 1 +2)
• Why are different species genetically different from each other?

  Different species have different genes

  Some species have the same genes but different alleles
• When investigating genetic diversity we can make comparisons between:

  • Characteristics
  • Base sequence of DNA
  • Base sequence on mRNA for the same gene
  • Amino acid sequences for the same protein
• Principles of natural selection:

  1. A population shows variation in phenotypes, due to different genotypes
  2. Variation can result from a random mutation leading to a new allele of a gene
  3. The new allele can benefit the individuals that have it - they are better adapted to their environment
  4. These individuals are more likely to survive and reproduce
  5. New allele is inherited by offspring in the next generation who also have better reproductive success
  6. Over many generations the allele frequency increases in the population
• Anatomical adaptations


  Camouflage

  Thick fur

  Sunken stomata

  Large beaks
• Behavioral adaptations

  Migration

  Playing dead

  Stealing food
• Physiological adaptations

  Hibernation

  Venom

  Lipid storage - for water conservation
• Directional selection

  Change in allele frequencies from the mean - 1 direction
• Stabilizing selection 


  Mean allele selected for and becoming more common, extreme phenotype selected against