This tutorial is Part 2 of a 10 part series.
Part 1, What is mtDNA?
Part 2, Facts about mtDNA <<== You are here
Part 3, Structure of mtDNA
Part 4, Ancestral Markers in mtDNA
Part 5, Detecting Markers in mtDNA
Part 6, Tracing Ancestry with mtDNA
Part 7, The Cambridge Reference Sequence
Part 8, mtDNA Test Types
Part 9, mtDNA Haplogroup Determination
Part 10, mtDNA Subclades
A good understanding of the basics of mtDNA will help you to better understand mtDNA ancestry discussions in this tutorial.
What does mtDNA look like?
1. Its round! Unlike the other DNA types in our body which are linear, mtDNA happens to be a round circle, called a “plasmid”.
2. It’s small! While nuclear DNA (DNA found in the nucleus of the cell) is a staggering 49,530,000 to 247,200,000 bases in length, mtDNA is only approximately 16,569 to 16,571 base pairs in length (don’t worry if you don’t know what a “base pair” is. We will be talking about base pairs in more detail later in this lesson).
Why is mtDNA so different from all of the other DNA in our body?
The strange appearance of mtDNA in comparison to the other DNA types in our body has something to do with its origins. Mitochondria has many of the same features as single cell organisms called “prokaryotes”. Bacterial cells are prokaryotes. The mtDNA that is found inside the mitochondria is a circular plasmid, just like the DNA in bacteria, which is also circular. The “endosymbiotic hypothesis” suggests that the reason for the extremely close resemblance of mtDNA to bacterial DNA is that 1.7 to 2 billion years ago, mitochondria were originally bacteria that were “engulfed” by a cell and became permanently incorporated in the cytoplasm of the cell. This is called a “symbiotic” relationship because the cell and the bacteria provided a survival advantage to each other (mitochondria produces energy “ATP” for the cell, and the cell provides protection). This explains why the mtDNA is circular and found in the cytoplasm instead of the nucleus of the cell.
What does mtDNA do? What is its function?
The mtDNA contains the genetic code for 37 very important genes (13 of the genes are responsible for producing proteins, 22 of the genes hold the genetic code to produce transfer RNA (aka tRNA), and 2 genes hold the genetic code to produce ribosomal RNA (rRNA), all are necessary for our survival). Thus, the mtDNA is very important, and when something goes wrong with the mtDNA, it can lead to mtDNA diseases such as exercise intolerance, Kearns-Syre syndrome and even death.
The 1) size, 2) structure and 3) importance of mtDNA for survival, all play a role in where ancestral markers are located in the mtDNA and will allow you to understand the testing methods used to detect ancestral markers in the mtDNA.