Non-random Mating and Dispersal

Inbreeding and Outbreeding

• Inbreeding: refers to (preferential) mating between biological relatives. As relatives (i.e., ancestors of the first individuals are shared with those of the second individual), they carry genes which are "identical by descent"; extreme inbreeding: mating between sibs, half-sibs, parent-offspring
• Outbreeding: (preferential) mating between non-relatives
• Positive assortative mating: mating among individuals who share particular genes or phenotypes
• Negative assortative mating: mating among individuals who do not share particular genes or phenotypes
• Inbreeding Coefficients:
  • Individual inbreeding coefficient (i.e., Pedigree inbreeding): F represents the probability that the offspring is homozygous due to identity by descent (ibd) at a randomly chosen autosomal locus, ranges in value from 0 (no locus ibd) to 1 (all loci ibd). Significant factors for pedigfree inbreeding are
    • Factors which determine the probability that various kinds of individuals will come into contact, e.g., population demography (sex ratio, birth or death rates), individual and population dispersal patterns, spatial distributions
    • Behavioral preferences for or against certain classes of individuals as potential mates. Behavioral preferences influence the acceptance or rejection of different types of individuals as mating partners
  • Population inbreeding coefficient: f measured by deviations from Hardy-Weinberg Equilibrium (a²+2aA+A²), examine for an over-representation of homozygotes. f ranges from -1 (inbreeding avoidance) to 0 (random mating) to 1 (inbreeding)
• Inbreeding depression: overrepresentation of homozygotes; e.g. matings between cousin are rare (0.05% in U.S.) but account for 20% of albinos; deficiency in immune systems; recessive, deleterious alleles occur more likely in homozygous condition; humans have on average 8 recessive, deleterious alleles. 1% increase in inbreeding produces 11% increase in the incidence of genetic deseases; Even small amounts of pedigree inbreeding in a random mating population greatly increase the incidence of some types of genetic disease. This is of particular concern in groups with small effective population sizes - Amish, Ashkenzi Jews
• Outbreeding depression: Extreme case, hybridization across genetically differentiated populations
• Outbreeding vs. Inbreeding Tradeoffs: hybrid vigor
• Advantages and disadvantages of dispersal/outbreeding: local conditions are suitable for reproduction, acquired resistance to disease, functional association of gene complexes shaped by local adaptations,
• Population genetics and the Rate of Evolution: Ground squirrels have matrilineal kin clusters and estrous is synchronized. Thus the same male is likely to mate with several closely-related females - genetic diversity of populations is primarily contained between kin clusters, high local levels of inbreeding assure the dispropotionately high expression of different genotypes - rapid rate of evolution in mammals

Dispersal

• <Dispersal>: Travel of Individuals, Ecological process affecting distribution, and genetic process affecting geographic differentiation and variation
• Philopatry: limited dispersal where average propagule (i.e. offspring) moves less than 10 homeranges away from natal site
• Vagrancy: wide dispersal where average propagule moves more than 30 homeranges away from natal site
• Successful dispersal: dispersal is successfull if propagule obtains opportunity to breed and raise young (i.e. genes migrate)

Reading Assignment

• Wikibooks: Animal Behavior - Chapter 4 (especially Population Genetics and Behavior)

Food for Thought

The contraceptive pill has been selected as one of the ten most significant discoveries of the last millennium due to its influence on human society. Is this justified?

Links of Interest

• Tay-Sachs Disease