Genetic Diversity

• Genetic diversity


  The genetic variation that exists within a species
• Individuals of the same species will have the same genes at the same loci but not necessarily the same alleles for each gene
• Gene pool


  Comprised of all the alleles of all the genes within a species
• Genetic differences or diversity between populations of the same species

  Increases the size of the gene pool
• Genetic diversity within a single population can also be observed
• Importance of genetic diversity

  • Creates a larger gene pool which can help the population adapt, and survive changes in the environment
  • Changes could be biotic factors such as new predators, pathogens and competition with other species or they could be abiotic factors like temperature, humidity and rainfall
• Measurements of genetic diversity

  • Proportion of polymorphic gene loci
  • Number of loci that have two or more alleles
  • Proportion of the population that is heterozygous for any specific gene locus
  • Allele richness - the number of different alleles that exist for specific genes
• All three measurements involve determining whether there are multiple alleles at a locus
• Phenotypes can sometimes be used to identify the presence of multiple alleles


  When each different allele is expressed in the phenotype of an individual they produce observable differences
• When different alleles do not always produce an observable change in the phenotype of individuals


  The DNA sequences or the protein products of the alleles must be examined and compared
• Some of the differences discovered might not be of major importance
• Genetic polymorphism


  When there are two or more alleles present at a single loci
• Monomorphic locus


  A locus that does not have multiple alleles
• Polymorphic locus


  A locus that has multiple alleles
• The most common allele must have a frequency less than 95% or 99% for a locus to be considered polymorphic
• Assessing genetic diversity of a species population

  1. Identify a number of gene loci to investigate

  2. Identify how many of these gene loci are polymorphic

  3. Divide the number of polymorphic gene loci by the total number of loci being investigated
• The proportion of polymorphic genetic loci (P) does not illustrate the allele richness of a breed or species
• Limitations of P


  • A study on different blood proteins in dogs found that all genetic loci were polymorphic, P= 1, but the number of alleles for each gene locus varied from 2 to 11
• Other methods to assess genetic diversity

  • Comparing the amino acid sequences of proteins (allozymes)
  • Comparing DNA sequences
• Nearly all of the genetic diversity assessment is now done at the level of base sequences, focusing on specific sequences in nuclear DNA and mitochondrial DNA (mtDNA)