L4 - genetic diversity

• $proportion\ of\ polymorphic\ gene\ loci\ =$$\ \frac{number\ of\ polymorphic\ gene\ loci}{total\ number\ of\ loci}$
• Genetic biodiversity: the proportion of gene variants within a species
• Locus (plural loci): the specific site on a chromosome where a gene is found
• Polymorphism: two or more alleles that occupy the same locus in a population (when a gene has two or more alleles)

  -this leads to phenotype variation, eg blood groups, dog breeds, flower colour, and increases genetic diversity
• Monomorphism: when a gene has only one type of allele. Most genes are ‘monomorphic’ this ensures that the basic structure of a species is similar (eg. the hox gene - body plan)
• Individuals of the same species have the same genes, but they may have different versions of the genes (alleles)
• Importance of genetic biodiversity:

  -large population have a greater genetic diversity (larger gene pool)

  -small populations have lower genetic diversity (shallow gene pool)

  -greater genetic diversity (large gene pool) increases the chance of some organisms having the traits/genes to survive

  -genes in small population (smaller gene pools) become more uniform and any disabilities in the genes are more likely to be expressed as phenotypes
• Genetic drift: the change in frequency of an existing gene variant in the population due to random chance

  -may cause gene variants to disappear completely and thereby reduce genetic variation

  -could also cause initially rare alleles to become much more frequent and even fixed
• Genetic drift:

  -can happen in all populations

  -has a drastic effect in small populations

  -driven by chance, not selection

  -two main types are founder effect and genetic bottlenecks
• GENETIC DRIFT: bottlenecks:

  -occurs when a population experiences a drastic reduction in size, leading to a loss of genetic diversity as certain alleles are lost or become more common due to chance

  -a random occurrence destroys part of the population (storm, poaching, disease)

  -the new, smaller population has a reduction in the gene pool due to a random event
• GENETIC DRIFT: founder effect:

  -occurs when a small group of individuals from a larger population establishes a new, isolated population, leading to a reduction in genetic diversity and potentially distinct allele frequencies compared to the original population
• Linking decreasing population numbers, inbreeding, and extinction events:

  1)when a population number drops (habitat destruction, new predator, pollution)

  2)the likelihood of inbreeding is increased

  3)this means disabilities or undesirable traits are passed on more frequently

  4)this leads to possible extinction events
• Extinction events are usually preceded by a drop in genetic biodiversity
• Drop in genetic biodiversity -> extinction
• The greater the proportion of polymorphic gene loci, the greater the genetic biodiversity within a species