What is Y-DNA?
Y-DNA refers to the DNA on the male sex chromosome – the Y chromosome. We each have 23 pairs of chromosomes: 22 pairs of autosomal chromosomes and two sex chromosomes – the X and Y chromosomes.
Females inherit an X chromosomes from each parent (but no Y chromosome), while males inherit an X chromosome from their mother and a Y chromosome from their father. Very little recombination (mixing) occurs between the X and Y chromosomes in males, hence the Y-DNA essentially remains unchanged through the paternal line, providing an incredibly useful way to trace paternal ancestry.
What is a Y-STR test?
A Y-STR test analyzes markers in the Y chromosome known as STRs or ‘short tandem repeats’.
STR markers are short segments of DNA (2-13 nucleotides in length), which are repeated multiple times. STR analyses measure the exact number of repeat units. The number of repeats differs between individuals because STRs change frequently. Closely related individuals will have similar Y-STR profiles compared to those that do not belong to the same paternal line.
Methods and analysis of Y-STR testing:
The Y-STR test determines the number of repeats at each marker tested – either 20, 44 or 101 markers, depending on the requested analysis.
When two individuals take a Y-STR marker test, their STR numbers can be compared to see if there is a match. The confidence with which the Y-STR test can predict a relationship between two individuals increases as more STR markers are tested.
A calculation called “TMRCA” (time to most recent common ancestor) can be performed to estimate how many generations ago the two males likely shared a common paternal ancestor. Comparing more Y-STR markers will provide a higher stringency comparison and a more precise TMRCA calculation.