Question

The shape of an underlying coalescent tree directly determines:

a) the distribution of fitness effects

b) the site frequency spectrum

c) the effective population size

d) the mutation rate

Please explain how you got your answer:)

Answer 1

ANS) The shape of an underlying coalescent tree directly determines

c) the effective population size.

It is a tree that shows how quality variations examined from a populace may have started from a typical progenitor. In the least difficult case, coalescent hypothesis expect no recombination, no normal determination, and no quality stream or populace structure, implying that every variation is similarly liable to have been passed starting with one age then onto the next. The model looks in reverse in time, blending alleles into a solitary hereditary duplicate as indicated by an arbitrary procedure in mixture occasions. Under this model, the normal time between progressive mixture occasions increments exponentially back in time.

Consider a solitary quality locus tested from two haploid people in a populace. The family line of this example is followed in reverse so as to the point where these two genealogies mix in their latest normal predecessor . Coalescent hypothesis looks to gauge the desire of this day and age and its fluctuation. The likelihood that two genealogies combine in the quickly going before age is the likelihood that they share a parental DNA succession. In a populace with a steady viable populace measure with 2Ne duplicates of every locus, there are 2Ne "potential guardians" in the past age. Under an irregular mating model, the likelihood that two alleles start from the same parental duplicate is consequently 1/(2Ne) and, correspondingly, the likelihood that they don't mix is 1 ? 1/(2Ne).

At each progressive going before age, the likelihood of combination is geometrically disseminated—that is, it is the likelihood of noncoalescence at the t ? 1 going before ages increased by the likelihood of blend at the age of intrigue:

P_c(t) = (1-1/2N_e) ^ t-1 (1/2N_e)

For adequately huge estimations of Ne, this dissemination is very much approximated by the persistently characterized exponential appropriation

P_c(t) = 1/2N_e ^ t-1/2N_e

This is numerically helpful, as the standard exponential dispersion has both the normal esteem and the standard deviation equivalent to 2Ne. Along these lines, in spite of the fact that the normal time to blend is 2Ne, genuine mixture times have an extensive variety of variety. Note that coalescent time is the quantity of going before ages where the mixture occurred and not schedule time, however an estimation of the last can be made increasing 2Ne with the normal time between ages. The above figurings apply similarly to a diploid populace of successful size Ne at the end of the day, for a non-recombining portion of DNA, every chromosome can be dealt with as proportional to an autonomous haploid individual; without inbreeding, sister chromosomes in a solitary individual are no more firmly related than two chromosomes arbitrarily examined from the populace. Some viably haploid DNA components, for example, mitochondrial DNA, nonetheless, are just conveyed by one sex, and in this manner have one quarter the compelling size of the comparable diploid populace (Ne/2)