It has been observed that Fst increases with the distance be

It has been observed that F_st increases with the distance between populations in many species. Explain why Let us imagine that we observe that F_st increases more rapidly with distance for mitochondrial DNA than for autosomal DNA for some species. Explain how this can happen. How might you differentiate your answers to part b

Solution

A. Fixation index (F_st) is a measure of population differentiation due to genetic structure. It is frequently estimated from genetic polymorphism data, such as single nucleotide polymorphism or microsatellites. Genetic distance is a measure of genetic divergence between species or between populations within a species.

A commonly used measure of genetic distance is the fixation index which varies between 0 and 1. A value of 0 indicates that two populations are genetically identical (minimal or no genetic diversity between the two populations) whereas a value of 1 indicates that two populations are genetically different (maximum genetic diversity between the two populations). No mutation is assumed.

Large populations between which there is much migration, for example, tend to be little differentiated whereas small populations between which there is little migration tend to be greatly differentiated. F_st is a convenient measure of this differentiation, and as a result F_st is the most widely used descriptive statistics in population and evolutionary genetics.

F_st is directly related to the Variance in allele frequency among populations and conversely to the degree of resemblance among individuals within populations. If F_st is small, it means that allele frequencies within each population are very similar, if it is large, it means that allele frequencies are very different.