One approach to studying the origins of modern humans is to examine mitochondria

Question

One approach to studying the origins of modern humans is to examine mitochondrial DNA (mtDNA) from populations around the world. Because a fetus develops from an egg containing its mother’s mitochondria (which have their own, non-nuclear DNA), mtDNA is passed entirely through the maternal line. Mutations in mtDNA can now be used to estimate the timeline of genetic divergence. The resulting evidence suggests that all modern humans have mtDNA inherited from a common ancestor that lived in Africa about 160,000 years ago. Another approach to the molecular understanding of human evolution is to examine the Y chromosome, which is passed from father to son. This evidence suggests that all men today inherited a Y chromosome from a male that lived in Africa about 140,000 years ago.

In your own words, explain how mtDNA and/or the Y-chromosome might be used to discover genealogical relationships of one’s own ancestors.

Explanation / Answer

mtDNA and/or the Y-chromosome might be used to discover genealogical relationships of one’s own ancestors.  

A genealogical DNA test is a DNA-based test which looks at specific locations of a person's genome in order to determine ancestral ethnicity and genealogical relationships. Results give information about ethnic groups the test subject may be descended from and about other individuals that they may be related to.

Three principal types of genealogical DNA tests are available, with each looking at a different part of the genome and useful for different types of genealogical research: Autosomal, Mitochondrial, and Y. In general, genealogical DNA tests do not give information about medical conditions or diseases.

mtDNA and the ancestors:

Genomic DNA is found in the cell nucleus and is passed down equally from both parents. Genomic DNA codes for all of your traits such as eye color, hair color, and just about anything that is inherited. Your cells also have another type of DNA called mitochondrial DNA. Mitochondrial DNA (mtDNA) is independent of nuclear DNA. While nuclear DNA is located in the nucleus of the cell, mitochondrial DNA is located in the mitochondria. Mitochondria is the organelle present in all cells which converts sugars into energy. Mitochondria is unusual in that it is the only organelles which has its own circular loop of DNA. Human mitochondrial DNA is much smaller than human nuclear DNA. Human nuclear DNA has around 3 billion base pairs or nucleotides, while human mitochondrial DNA only has 16,600 base pairs. Mitochondrial DNA is inherited from the mother alone, rather than being inherited from the father and the mother. Additionally, recombination (or crossing over) does not occur in mitochondrial DNA (mtDNA). For both of these reasons, the sequence of mitochondrial DNA stays the same over generations, and thus is a useful tool for looking at maternal ancestry. Scientists have found that the mitochondrial genome mutates 5-10 times faster than nuclear DNA. One type of mutation, called a single nucleotide polymorphism (SNP), is a single base pair in a DNA sequence that has been swapped out for a different nucleotide. Below is an example of a SNP.

Human Migration Patterns Scientists can gather clues about ancient human migration patterns by studying the patterns of SNPs in a modern day population. When a group of people share similar SNPs, they are part of the same “haplogroup”. Scientists associate different haplogroups with different geographic locations on Earth such as “Africa”, “Asia”, “the Americas” and “Europe”. By categorizing an individual into a haplogroup, it is possible to trace migration routes by observing the branching points in an ancestral map containing all known haplogroups. Most scientists believe that all humans originated in Africa from a single female ancestor they named “mitochondrial Eve”. This “Eve” was not the first female human, nor was she the only human alive at that time, but for some reason all of Eve’s descendants survived to form the entire human species. The climate of Earth changed, causing humans to migrate out of Africa in search of food.

mtDNA and Y-chromosome might be used to discover genealogical relationships of one's own ancestors:

The information on this page is meant to provide a very simple explanation of your Y-DNA and mtDNA Ancestry used for genealogical purposes. Scientists estimate that the total amount of Y-DNA of a man is less than 1% and the total amount of mtDNA in either a man or a woman is less than 1%. It is important to understand that after taking a Y-DNA and an mtDNA test, the majority of everyone's DNA remains untested and it is called Autosomal DNA, with another 5% of a female's DNA or 2 1/2% of a male's DNA being x-chromosomal DNA. In a man this would mean roughly 95.5% of his DNA is Autosomal and in a woman that figure would be roughly 94%. Click here to find out more about a human's total DNA makeup.

The two basic tests used for genealogy purposes are Y-DNA tests (male) and mtDNA tests (female). Both tests, the Y-DNA and the mtDNA, sample a very small amount of your total DNA and as genetic genealogists know, the test most taken is for Y-DNA. It can show a relationship between two males; genetic cousin is a term that is commonly used. The mtDNA test is less practical for genealogical use because traditionally the female's birth or maiden name changes from generation to generation. With that said, mtDNA still may be used to prove scientifically that two people (male or female) share a common maternal ancestor, although it is more effective at proving two people do not share a common maternal ancestor.

Below is a simplistic chart showing two children, a brother and a sister. In addition to them, their parents, grandparents, great grandparents and gg grandparents are also shown for visualization of their DNA Ancestry. Note how the brother has a two color graphic to show how he carries both Y-DNA and mtDNA. The brother's sister has a one color graphic; this is to show that she only carries mtDNA.

For the purposes of our Phillips DNA study, a male DNA participant who tests both Y-DNA and mtDNA will have two EKA's (Earliest Known Ancestors). One will be a paternal ancestor (straight line father's Y-DNA) and the other a maternal ancestor (straight line mother's mtDNA).

Since women do not have Y-DNA, a female will only have one EKA that is associated with her DNA test, her maternal ancestor (straight line mother's mtDNA). See the chart below to help visualize the Y-DNA and mtDNA Ancestry of the two test participants, the previously mentioned brother and sister..

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.