AQA A Level Biology

Revision Notes

4.4.1 Genetic Diversity

Genetic Diversity

  • Organisms of the same species have very similar genomes, but two individuals (even twins) will have differences between their DNA base sequences
  • Considering the size of genomes, these differences are small between individuals of the same species
  • The small differences in DNA base sequences between individual organisms within a species population are called genetic variation
  • Genetic variation is transferred from one generation to the next and it results in genetic diversity within a species population
  • Genetic diversity is the number of different alleles of genes in a population
  • Mutation results in the generation of new alleles and contributes to genetic diversity or the size of the gene pool
    • The new allele may be advantageous, disadvantageous or have no apparent effect on phenotype (due to the fact that the genetic code is degenerate
    • New alleles are not always seen in the individual that they first occur in
    • They can remain hidden (not expressed) within a population for several generations before they contribute to phenotypic variation

Effects of genetic diversity

  • There needs to be some level of genetic diversity within a population for natural selection to occur
  • Differences in the alleles possessed by individuals within a population result in differences in phenotypes
  • Environmental factors affect the chance of survival of an organism; they, therefore, act as a selection pressure
  • Selection pressures increase the chance of individuals with a specific phenotype surviving and reproducing over others
  • The individuals with the favoured phenotypes are described as having a higher fitness
    • The fitness of an organism is defined as its ability to survive and pass on its alleles to offspring
    • Organisms with higher fitness posses adaptations that make them better suited to their environment
  • A population with a large gene pool or high genetic diversity has a strong ability to adapt to change
  • If a population has a small gene pool or very low genetic diversity then they are much less able to adapt to changes in the environment and so can become vulnerable to extinction
    • Cheetahs are an example of a species with a small gene pool
    • They experienced a very large decline in numbers approximately 10,000 years ago
    • This left small, fragmented populations of individuals remaining
    • There was no mixing between populations and large amounts of inbreeding occurred
    • This is problematic for conservation as low genetic variation means the species are less likely to be able to respond (survive) in the event of any environmental changes

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top