Conservation of Genetic Resources: Population Genetics

Population Genetics

• Population genetics is the study of genetic variability by describing changes in allele frequency for a particular trait over time and analyzing the causes of those changes.
• It is the application of Mendel's laws and other genetic principles to entire populations of organisms instead of just individuals.

Definitions

• Phenotype: describes all traits of an individual concerning its morphology, physiology, ecological relationships, and behavior.
• Genotype: is the description of the complete set of genes that an individual inherits from its parents.
• Gene: the basic physical and functional unit of heredity, passing information from one generation to the next.
• Allele: any of the alternative forms of a gene that can exist at a single locus.
• Allele frequency: the proportion of all alleles of that gene in the population that are specifically this type.
• Genotype frequency: the frequency of a given genotype in a population.

The Hardy-Weinberg Principle

• States that sexual reproduction does not reduce genetic variation generation after generation; on the contrary, the amount of variation remains constant if no disturbing forces are acting against it.
• Assumes:
  • Sexual reproduction
  • Non-overlapping generations
  • Random mating
  • Very large population size
  • Negligible migration
  • No natural selection
  • No mutations

Reproduction and Mating Systems

• Inbreeding coefficient (F): measures the reduction of heterozygosity
• H: actual frequency of heterozygotes in the population
• H0: expected number of heterozygotes under random mating

Forces Shaping Genetic Diversity

• Mutation: the ultimate source of variation, may be caused by spontaneous mutation or damage by radiation or chemical mutagens
• Migration: increases diversity, rate of change in gene frequency is proportional to the difference in frequency between the recipient population and the average of the donor populations
• Recombination: generates new combinations of existing diversity, does not create new diversity
• Selection: acts on the inherited ability of organisms to survive and reproduce, leading to an increase in superior genotypes

Genetic Drift

• Homozygosity: fixation and loss of alleles
• Subpopulation differentiation: leads to genetic drift
• Bottleneck: develops when the population size sharply drops, leading to loss of alleles
• Founder effect: occurs when a few individuals colonize and become established in a new environment, leading to genetic drift
• Population size: affects genetic diversity, heterozygosity declines with smaller population size
• Allele loss: occurs at a rate dependent on population size and allele frequencies