Topic 8: Inbreeding Flashcards
What is the inbreeding coefficient?
The probability that two alleles in an individual are identical by descent, or are autozygous.
How do you determine relatedness?
Usually measured from a pedigree by counting the number of common ancestors in a lineage.
You do (1/2) to the power of however many common ancestors there are, and then multiplied by 1+the inbreeding coefficient of the common ancestor.
If there are multiple different paths then you add the equation for each pathway
What is another way you can measure the inbreeding coefficient for an individual?
It is half the relatedness of the parents.
What is the relationship between heterozygosity and individual inbreeding?
The inbreeding coefficient describes how much less heterozygosity we will observe within an inbred individual than we would expect to see under random mating.
Fx is expected heterozygosity minus observed heterozygosity and then divided by the expected heterozygosit
What is the difference in calculating inbreeding at the population level compared to individual level?
Same formula, but instead of using observed heterozygosity of the individual, we use the observed heterozygosity at the population level.
What does an inbreeding coefficient that is at, below or above 0 mean?
f is less than 0 = outbreeding, breed with less related individuals, inbreeding avoidance
f is 0 = random mating, HWE, do not trend towards mating with relatives or non-relatives
f greater than 0 = inbreeding, self-fertilizing, may be purposeful
What does f mean for a population?
The rate of reduction in heterozygosity per generation due to inbreeding in a population, and it changes the expected genotype frequencies under HWE
Results in loss of heterozygosity and gain of homozygosity
What type of statistical test do we use to test whether a locus (for inbreeding) is not in HWE?
What are the parameters that you need for this test?
How do you know whether your results are significant?
The null hypothesis is that the population is not out of HWE, and the alternate hypothesis is that the population is out of HWE
Need observed count, expected count, and degrees of freedom
Df = #categories - 1 - #parameters estimated
also can be thought of like #genotypes - #of alleles
What is outbreeding? What is the fitness benefit of outbreeding called?
The opposite of inbreeding, occurs when mated individuals are less related than expected by chance
Leads to increased genetic diversity
The fitness benefit of outbreeding is called “hybrid vigour” or heterosis, which is the opposite of inbreeding depression
What is outbreeding depression?
Occurs when two groups have been separated for so long that they have evolved different groups of adapted genes, and crossing them reduces their fitness
What is the continuum from inbreeding to outbreeding?
Self-fertilization
Incestuous inbreeding
Positive assortative mating (seek relatives)
Random mating
Negative assortative mating (seek non-relatives)
Hybridization (different species)
What is the effect of inbreeding on the fecundity and lifespan of males?
They have lower numbers of children, and they have lower reproductive lifespan
Inbreeding depression in males
What are two ways that you can reverse the effects of inbreeding?
Genetic restoration and rescue
What is selfing? What are some advantages?
Extreme form of inbreeding, common in invertebrates and plants.
Advantages: do not have to find a mate, do not need pollen vector or large numbers of pollen, pass on 100% of genes to offspring, genetic purging of deleterious alleles (recessive
What are some features associated with selfing?
Small petals, no scent, no pollinator reward, reduction in pollen production, shorter distance between stigma and anther (male and female parts of the plant)
