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Genealogy is all the rage these days, and DNA testing has made tracing family lines even more expansive than it used to be. How exactly is this accomplished though? How is genetic testing able to trace family lines back centuries? That has to do entirely with how our genomes are passed down to us.

Back to the Basics

Before discussing how families can be traced through genetic testing, first one must understand the basics of how genetics work. As you may remember from your high school biology courses, part of your genome is inherited from your mother and part from your father. The reality is a little more complicated than that.

To start, it all goes back to meiosis. Meiosis is the process by which gametes and zygotes are formed. These are the initial cells which will be fertilized to grow into new living beings.

Meiosis occurs in eight stages with Prophase I being the important stage for our discussion. During Prophase I, the chromosomes condense and are able to exchange genetic material. Meiosis then continues until Telophase II and cytokinesis. The end result of meiosis is is four daughter cells each with unique genetic material and half the number of chromosomes. When fertilization occurs, two of these daughter cells fuse to from the zygote which eventually becomes a fetus.

Assumptions versus Reality

So siblings should then share roughly 100% of their genetics with each other right? No.

Remember that exchange of genetic material in Prophase I of meiosis, that exchange happens differently each time that meiosis occurs. Due to that fact, full-blooded siblings share anywhere from 38-61% of their DNA with each other and 50% with the parent. That percentage decreases the further your family tree spreads.

Then how can genetics and DNA be used to trace your lineage through the centuries? The answer comes in the form of mitochondrial DNA.

What is mitochondrial DNA?

Mitochondrial DNA is DNA found in the mitochondria of cell. When the gametes are being formed through meiosis, the organelles (including the mitochondria) are also replicated. Unlike the chromosomes, however, the mitochondria is copied without that genetic exchange. This means that the mitochondria is inherited without change from the parent cell to the daughter cells minus potential mutations.

This mitochondrial DNA is then inherited directly from the mother to the child without change assuming no mutations arise during replication. Since this DNA is inherited directly from the mother to the child, your genetic lineage can then be traced through the centuries.

So while the DNA you inherit from your father is important for providing genetic variably and making you you, the DNA you inherited from your mother through her mitochondria allows you to trace your ancestry from your mother to her mother and so forth.

~~ Emily H. – MS Biochemistry (BS Cellular and Molecular Biology and Biochemistry) Return to home