Y Chromosome DNA (Y-DNA) - Nuclear DNA information which is found in the Y Chromosome which only exists in males. The Y Chromosome is passed along from male to male via a sperm cell which contained the Y Chromosome of the father. The sperm cell having a Y Chromosome determines that the child will be male. Thus only males have the Y chromosome and only males can pass along the Y chromosome from father to sons.
Mitochondrial DNA (mtDNA) - Non-nuclear DNA which is a small DNA molecule contained in the Mitochondria (mtDNA) organelles which are located inside the cells of all of a mother’s children, both male and female. The Mitochondria organelles are not in the nucleus of the cell but are outside the nucleus. Thus mtDNA is not nuclear DNA and is found inside the Mitochondria organelles located inside the cell but outside the nucleus of the cell. We get our Mitochondria only via the egg cell of our mother. Thus only females can pass on MtDNA to their offspring.
Types of DNA of Most Interest to Genealogists?
A) Y Chromosome (Nuclear) or Y-DNA
All men and only men have a Y chromosome. This biological fact allows us to trace back in time a direct, largely unchanged genetic line of inheritance from father to son.
Every person, male or female has 22 matching pairs of chromosome -- one inherited from each parent -- but the 23rd pair is different. This unmatched pair, known as the X and Y gender chromosomes, determines whether we are male (XY) or female (XX). A mother always provides a single X chromosome in her egg. Inherit an X from your father and you will be a female, receive a copy of his Y and you will be male. And so the Y chromosome travels from father to son with each successive generation of males.
The second thing that makes the Y chromosome unique is that the information carried on Y-chromosomes is inherited largely intact over time. Unlike other chromosomes, the genetic material on the Y chromosome is not mixed with each new generation. The reason is that when cells divide in preparation to make sperm and egg, all 23-chromosome pairs line up to exchange random bits and pieces of DNA with their matching partner before separating. All the chromosomes do this exchange of genetic material save the mismatched XY pair. The Y is much shorter and very little of its genetic information is broken up in an exchange of DNA with the X chromosome. The information carried on the Y chromosome travels from father to son as a nearly exact copy of itself.
Occasionally, during the DNA copying process small changes or mutations occur, and it is these mutational differences that allow us to distinguish the Y chromosome of an individual from his ancestor's. Thus an actual genetic record of the male line going back through time exists -- as clear a marker of paternal heritage as a father's family name.
A tangible timekeeper of history, the Y chromosome allows us to trace human evolution, track migration patterns and relatedness in groups of people, and answer paternity questions going back generations. As we pull apart the Y chromosome, we begin to unravel some fascinating stories about our own origins.
B) Mitochondria or mtDNA
Mitochondria--The energy component in all cells in the human body, is passed from mothers to all their children through the union of the mothers egg and the male’s sperm. Mitochondria organelles are located outside of the cell’s nucleus and have their own DNA. The mtDNA molecule is much shorter than the nuclear DNA. It is only about 16,500 base pair in length and it is arranged in a small circle like a donut. Compare that to nuclear DNA which is about 3.2 billion base pair in length and is arranged in a long spiraled and coiled thread like structure. The typically basic mtDNA test yields a standardized result of 400 base pairs that are compared to the Cambridge Reference Sequence (CRS). The results of the test, which will include the Hyper Variable Section #1 of the control area of the mtDNA, will yield a few base pairs that differ from the standard Cambridge Reference Sequence (CRS). Since the standard was created around a western European woman, the more changes one has from the standard the farther back in time one’s mtDNA would have split from the base of the genetic tree. For example most Africans have 7 or 9 differences while most Europeans have a few or perhaps 5 of these polymorphism from the Cambridge Reference Sequence (CRS). One’s maternal ancient Haplogroup is determined from the basic mtDNA test. Advanced, refined, or so called mtDNA Plus tests also test a second region of the mtDNA called Hyper Variable Section #2. The additional data from the second Section when combined with the first section results allows greater differentiation between individual’s maternal line and reduces the time to your most recent common maternal ancestor when you have an exact match between two people for both HVS1 and HVS2.
The Anthropologists have broken down human mtDNA into about 30 distinct groups called Haplogoups, with many sub groups assigned to each group.
If you match someone on the mtDNA side you will know that you and they share a common female ancestor, but the time to the MRCA is typically several thousand years ago, and certainly not less then many hundreds of years group. FTDNA, the company I use for testing, also offers an refined/enhanced mtDNA Plus test that examines the HVS2 section of the Mitochondria to reduce the time predictions to the Most Recent Common Ancestor (MRCA) in the female direct line.
