Question

According to their calculation of theta, the long term mtDNA Ne= 5000. Now assume that a single African mtDNA lineage migrates from Africa to European Neanderthals. How many years will it take before this single mtDNA lineage would fix in the Neanderthalhals population? Assume 30 years per generation.

Answer 1

For the mtDNA,
Effective population size = nucleotide diversity population parameter (theta) /3 * mutation rate (mu)
Human mitrochondrial DNA mutation rate is calculated approximately as 2.7 * 10^-5 per nucleotide base per generation.
5000 = Theta / (3 * 2.7*10^-5)
theta = 5000 * 3 * 2.7*10^-5
theta= 0.405 is the nucleotide diversity population parameter in a generation.
nucleotide diversity population parameter indicates the degree of nucleotide polymorphism.

If the mutation rate is negligible and the changes in the nucleotides are fixed in the population, then
population size will be 0.405/(3*0.001) = 135
The mtDNA is fixed in the European Neanderthals with population size of 135.

Now, to know in how many generations the mutation rate becomes negligible by fixing the lineage in the neanderthals,
the no. of generations would be 5000/135=37 generations.
The number of years for 37 generations would be 37*30yrs per generation = 1110 years.
Therefore, it takes 1110 years before the mtDNA gets fixed in the Neanderthal population.