inbreeding, outbreeding and implications for conservation biology Flashcards
fitness-related characters
survival, growth rate and fertility
inbreeding coefficient
the probability that two alleles in an individual were both descended from a single allele in an ancestor (ie they are ‘identical by descent’)
mutation-selection balance
the balance between mutations that introduce deleterious alleles into the population and the removal of such alleles by natural selection. The result is that such mutations are present at low frequencies but, despite selection, are never entirely absent.
what’s the effect of inbreeding on fitness-related characters?
Those fitness-related characters are lowered - major abnormalities are more common in inbred families than in outcrosses eg mutant phenotypes that affect early development or genetic diseases (humans).
How is inbreeding depression detected?
Lower fertility, survival and growth rates for individuals with high inbreeding coefficients.
define heterosis or hybrid vigour
increased performance in F1 (first filial generation) eg studied in crops wrt economically important traits like drought tolerance, disease resistance and yield
What’s the genetic basis of inbreeding depression?
caused by increased homozygosity of individuals: 2 ways:
increased homozygosity for partially recessive detrimental mutations;
increased homozygosity for alleles at loci with heterozygote advantage (‘overdominance’). Deleterious alleles will generally be present in populations at low frequencies (mutation-selection balance), whereas overdominant alleles at a locus are maintained at intermediate frequencies by balancing selection.
explain balancing selection
selection - such as heterzygote advantage and frequency-dependent selection - that maintains genetic variants in a population
explain purging
reducing the frequencies of deleterious mutations in inbred populations, thereby lowering the mutational load (the presence of deleterious mutations in populations).
explain balancer stock
A strain of fly that contains a chromosome with genetic markers and with an inversion to prevent recombination with other arrangements. Such chromosomes are used to breed stocks with ‘extracted’ wild-type chromosomes fro estimates of homozygous and heterozygous effects.
Describe two methods of detecting inbreeding depression and genetic load using genetic markers
Use of inbreeding coefficients estimated from frequencies of homozygotes and heterozygotes for genetic markers or SNPs;
Examination of genetic rations at marker loci: deficiency of one homozygote in families or a significant heterozygotes excess in a family (or in inbred lines relative to the heterozygote frequency predicted for neutral alleles by the inbreeding coefficient) suggests inbreeding depression due to identity-by-descent for a gene linked to the marker.
cause of inbreeding depression due to increased homozygosity and hybrid vigour (heterosis)
arise from generally lower fitness of one or both homozygotes compared with the heterozygotes.
Genetic explanations involve the dominance levels of the alleles
how do we study the genetic causes of inbreeding depression?
integrate genetic and population results from genetically tractable organisms (rather than humans)
One eg is to test whether mutations can account for the observed extent of inbreeding depression
Are deleterious mutations present in natural populations?
Yes! eg in Drosophila melanogaster - rare recessive lethals - heterozygotes for lethal chromosomes isolated from different wild individuals are almost always viable - indicates they are recessive.
