mtDNA Genetics

What is mtDNA?

Mitochondrial DNA (mtDNA) is found in the mitochondria of human cells. Each cell can contain several mitochondria, and each mitochondrion contains dozens of copies of mtDNA. So in every cell there can be thousands of copies of mtDNA. This is different from nuclear DNA, since we only inherit two copies of the autosomal and sex chromosomes per cell.

All of us inherit our mtDNA from only our mothers. This mtDNA essentially remains unchanged through the maternal line, providing an incredibly useful way to trace maternal ancestry.

What is mtDNA sequencing?

The circular mitochondrial genome has three regions – two small hypervariable (HVR) regions and a large coding region. It is possible to sequence just the HVR1 region, both hypervariable regions (HVR1 and HVR2), or the complete mitochondrial genome (HVR1, HVR2 and the coding region).

The hypervariable regions comprise approximately 1100 bases of the mtDNA genome. Most of the variation in the mtDNA occurs in these regions. If two people have a perfect match at their HVR1 and HVR2 regions, further analysis of the much larger coding region can provide a higher stringency comparison and further resolution. The coding region covers the remainder of the mitochondrial genome and the complete mitochondrial genome is 16,569 base pairs.

What’s Included?

The entire DNA sequences for regions tested are provided to you in your mtDNA test report. Your mtDNA sequencing results are compared to a reference sequence called the “rCRS” (revised Cambridge Reference Sequence), and all of the positions within your mtDNA, which differ from rCRS are listed in your report.

Your unique mtDNA sequence result is known as your mtDNA profile.

Since mtDNA is passed down from mother to child along the direct maternal lineage, people who have descended from the same maternal lineage are expected to have exactly the same or very similar mtDNA profiles.

If two people have different mtDNA profiles, it conclusively confirms that they did not descend from the same maternal lineage.

Y-DNA Genetics

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.