This tutorial is Part 5 of a 9 part series.
Part 1, What is Y-DNA?
Part 2, Types of Ancestral Markers in Y-DNA
Part 3, STR Markers in Y-DNA
Part 4, STR Markers in Y-DNA - Y-DNA STR Marker Testing
Part 5, STR Markers in Y-DNA - What is Genetic Distance? <<== You are here
Part 6, STR Markers in Y-DNA - What is the Time to Most Recent Common Ancestor (TMRCA)?
Part 7, STR Markers in Y-DNA - Why test more STR markers?
Part 8, SNP Markers in Y-DNA - Y-DNA Haplogroup and Subclade Determination
Part 9, SNP Markers in Y-DNA - Summary of Y-DNA Test Types
After you test your Y-DNA STR markers, you can compare your markers against the markers of any other male individual to see whether you share a common male ancestor. If a match is found, you can determine the TMRCA (time to most recent common ancestor), a measurement of approximately how long ago you and the matching individual shared the common ancestor.
A key measurement value when comparing the Y-DNA STR markers between two different individuals is Genetic Distance.
Genetic distance is a measurement of the total difference in allele values of different genetic markers between two individuals. The smaller the value of the genetic distance for a given set of STR markers, the closer two individuals are related, and the more recently they shared a common ancestor (TMRCA). The method used to determine genetic distance for four different Y-DNA STR marker types is explained below.
A. Calculation of genetic distance for single-copy Y-DNA STR markers
For single-copy STR markers, the calculation is straightforward. The genetic distance for each single copy marker between two individuals is the absolute value of the difference between the value of the markers:
The total genetic distance between two individuals is the sum of the genetic distances of all markers compared.
B. Calculation of genetic distance for multi-copy markers Markers DYS385, DYS459, DYS464 and YCAII are multi-copy Y-STR markers.
For most multi-copy markers, genetic distance can be calculated by adding the differences in allele values for each of the two copies.
C. Calculation of genetic distance for multi-copy marker DYS464 - using Infinite allele model
Assuming mutations at different copies of the same marker took place in a single generation, the Infinite allele method counts the total difference between all copies of the same marker as 1, despite the fact that more than one mutation exists.
The genetic distance for DYS464 is calculated using this method. Regardless of the number of mismatches in DYS464, the genetic distance is always reported as a maximum of 1. Please remember that “genetic distance” is not the same as “mismatching markers”.
D. Calculation of genetic distance for DYS389i/ii
DYS389i is embedded in DYS389ii; therefore, the DYS389i values are included in DYS389ii values. Genetic distance can be determined by adding up two differences: differences in DYS389i values and differences in the second part of DYS389ii values, which are obtained by subtracting the DYS389ii values by DYS389i values.
The DNA database will automatically calculate the Genetic Distance and TMRCA values between you and your matches. You can also perform your own matches by plugging in the marker values at www.dnacalculator.org.