Coalescence Time Calculator

In population genetics, coalescence time is the estimated point in the past when a set of sampled gene copies last shared a common ancestor — a key measure for understanding genetic diversity and evolutionary history. Enter your Effective Population Size (Ne), Sample Size, Mutation Rate, Generation Time, and Ploidy into the Coalescence Time Calculator to find the Expected Coalescence Time in generations and years. Secondary outputs include the Population Mutation Parameter (θ) and Watterson's Estimator of genetic diversity.

Number of breeding individuals in the population

Number of alleles sampled from the population

Per-site mutation rate per generation

years

Average time between generations

Results

Expected Coalescence Time

--

Coalescence Time in Years

--

Population Mutation Parameter (θ)

--

Watterson's Estimator

--

More Biology Tools

Frequently Asked Questions

What is coalescence time in population genetics?

Coalescence time is the expected number of generations back to the most recent common ancestor (MRCA) of a sample of alleles. It represents how long ago all sampled alleles shared a common ancestral copy.

How does effective population size affect coalescence time?

Larger effective population sizes lead to longer coalescence times. In larger populations, it takes more generations for lineages to coalesce because there are more potential ancestors at each generation going backward in time.

What is the relationship between mutation rate and coalescence?

Mutation rate affects the population mutation parameter θ = 4Neμ (for diploids). Higher mutation rates increase genetic diversity and can be used to estimate coalescence times from observed sequence variation.

Why is sample size important in coalescence calculations?

Sample size determines how many lineages we're tracing back in time. Larger samples generally have more recent common ancestors because more lineages increase the probability of recent coalescence events.

What is Watterson's estimator?

Watterson's estimator is a method to estimate the population mutation parameter θ from the number of segregating sites in a DNA sequence sample. It's based on the expected number of mutations in the genealogy.

How does ploidy affect coalescence calculations?

Ploidy affects the effective number of gene copies in a population. Diploid organisms have twice as many gene copies as haploids, which influences the coalescence rate and population genetic parameters.

Can this calculator be used for all species?

This calculator provides general coalescence estimates but assumes random mating and neutral evolution. Results should be interpreted carefully for species with complex mating systems, population structure, or strong selection.