Topic 7: Relatedness Flashcards
TRUE OR FALSE: You do not need a pedigree to calculate relatedness
TRUE
What is one way of thinking about relatedness?
The fraction of shared alleles that are identical by descent between a pair of individuals.
What is the coefficient of relatedness (rxy)?
The average probability that a pair of alleles drawn from two individuals are identical by descent. In theory, offspring and parents are 0.5, full sibs are 0.5, half sibs are 0.25, offspring to grandparents are 0.25, and first cousins are 0.125
How do you get relatedness from pedigrees?
Trace all pathway of descent between the two individuals, then multiply each segment together. If the two individuals share more than one parent, then add the values of both of the pathways together.
What is Hamilton’s rule and the context of relatedness?
Hamilton’s rule is that altruism will occur when the fitness cost to the actor (c), is LESS than the product of the fitness benefit (b) to the recipient and the recipients relatedness to the actor.
Fitness is not only reproductive success but also genetic success, and individual fitness can be increased by performing altruistic behaviours that benefit related individuals who carry related genes to the next generation.
b can also be benefit to the individual
Why do we see adoption happen in the wild?
Adoption is always between kin, while orphans without kin are never adopted.
Cost of adoption increases with the foster mother’s litter size and the benefit for the offspring decreases with litter size.
Therefore rb is a function of relatedness and litter size when it comes to adoption
What are the two ways we can estimate rxy when pedigree information is not available?
- From multilocus DNA fingerprints (minisatellites) based on shared bands
- From single locus data (microsatellite), based on allele and genotype frequencies
What is the difference between Sij and S bar?
S bar is the average pairwise band sharing between two individuals, and it accounts for the background level of band sharing found in the population. The denominator here is the number of pairwise comparisons made between the samples.
What is E(sxy)?
The expected level of band-sharing between two individuals that are related. You can rearrange this for the relatedness
What is the difference between using fingerprints and single locus data?
Fingerprints uses bandsharing and single locus data uses allele and genotype frequencies
When using microsatellite data what values do you assign each locus depending on whether they share two alleles, one allele and no alleles?
1= both alleles shared
0.5= 1 allele shared
0= no alleles shared
You add up all these values for each locus and then divide by the number of loci looked at.
What is Queller and Goodnight relatedness?
Relatedness value that takes into account allele frequencies, therefore sharing more rare alleles is given more value than sharing common ones.
How do you combine loci information for mutli-locus samples using Queller and Goodnight relatedness?
YOU ADD THE RATIOS FROM EACH EQUATION. Make sure to keep the ratio to use if you are investigating more than one loci, because you must add the numerators and denominators to combine them.
How do you get the average relatedness over the two loci?
You take the results from adding the ratios for rxy and ryx for both different loci, then you add them and divide by 2
What does it mean if relatedness estimators take on negative values?
This means that the two individuals share fewer bands than the average and therefore are not closely related. BUT if you go back enough generations, then the relatedness will always be greater than one.
