Obviously, there was no point in history in which the clade that developed into ‘humanity’ consisted of only one female individual. Yet
every mitochondrial genome in any current human population can be traced back to a single woman: ‘Mitochondrial Eve’. She lived between 100,000 and 200,000 years ago in sub-Saharan Africa. How can we all be matrilineally descended from one woman? Explain, with diagrams as necessary.
To understand how we are all matrilineally descended from one woman, we need to examine how mitochondrial DNA (mtDNA) is passed down through generations.
Mitochondria are structures within our cells that have their own DNA, separate from the DNA found in the nucleus of our cells. During reproduction, the paternal DNA in sperm only contributes to the DNA found in the nucleus of the fertilized egg, while the maternal DNA in the egg contributes to both the nuclear DNA and the mtDNA.
Unlike nuclear DNA, which can undergo recombination and genetic exchange during reproduction, mtDNA is inherited intact from the mother, without any mixing or reshuffling of genetic material.
Here's the step-by-step explanation:
1. In the diagram, let's represent generations vertically, with the oldest generation at the top and subsequent generations below.
2. At each generation, the males and females are represented by squares and circles, respectively.
3. Let's start with 'Mitochondrial Eve.' She is represented by a circle at the top of the diagram. She lived around 100,000 to 200,000 years ago in sub-Saharan Africa. It's important to note that 'Mitochondrial Eve' is not the only woman alive at that time, but she is the most recent matrilineal ancestor of all living humans.
4. 'Mitochondrial Eve' had daughters, who inherited her mtDNA. These daughters are represented by circles below her.
5. Each of these daughters, in turn, had their own daughters, passing down their mtDNA to the next generation.
6. This process continues with each generation, with the maternal lineage passing on the mtDNA intact.
7. Over thousands of generations, the mtDNA passed down from 'Mitochondrial Eve' continued to be inherited by subsequent generations of females.
8. As human populations expanded and migrated, different lineages emerged, but all these lineages can ultimately be traced back to the original 'Mitochondrial Eve.'
Therefore, while individuals have nuclear DNA inherited from both parents, we can trace our direct maternal genetic lineage back to 'Mitochondrial Eve.' It's important to note that this does not mean she was the only woman alive at that time, but rather that other maternal lineages did not have unbroken female-to-female transmission of mtDNA up until the present day.
Please keep in mind that the diagram is a simplified representation, and in reality, the branching of lineages would be more complex as various migrations and genetic intermixing occurred.