Question

Explain why the same individual can be told they have different ancestry composition when the same data is analysed by different ‘studies’. What other factors do you think might affect the outcome of such tests (4 marks, 4-6 sentences max)? Note: this is not asking about the same data analysed with different stringency values.

What are some of the genetic techniques that are currently used to identify ancestry?

Answer 1

• It seems like brothers and sisters should have the same ancestry background. After all, they both got half their DNA from mother and half from father.
• But because of how DNA is passed on, it is possible for two siblings to have some big differences in their ancestry at the DNA level. Culturally they may each say they are “1/8th Cherokee” but at the DNA level, one may have no Cherokee DNA at all.
• DNA isn’t passed down from generation to generation in a single block. Not every child gets the same 50% of mom’s DNA and 50% of dad’s DNA. (Unless of course they are identical twins).
• Let us understand by an example, One way to think about this is to imagine DNA as a bunch of colored beads. Since we are interested in ancestry here, we will say that different colors mean different ancestries.Imagine that a man from Japan marries a woman from Europe. Her DNA happens to be 100% European and his 100% Asian. Let’s say that the European beads are red and the Asian beads are blue.
• When these two parents have a child, that child will get a random half of mother's beads and random half of Father's.This child is 50% European and 50% Asian.n this case you can see that each child actually shares the same ancestry even though they got some different DNA from each parent. They are each 50% European and 50% Asian.
• Let’s now imagine a couple of more complex situations. First we will add in some green beads from sub-Saharan Africa i.e. mother has small bit of African ancestry in her family tree which is common in U.S. else, everything is same Red is European, blue is Asian.
• Now, one child would not have green beads which means that he or she has 0% African DNA while another child would carry green bead which means that he or she would have African DNA even though it have same ancestry(parents).
• This process happens with each pair of chromosomes. And happens in new combinations with each egg (or sperm for dad). Infinite combinations are possible! Which is why two siblings can end up with different ancestries with the same parent.
• There are three major types of DNA tests to identify ancestors:

1. Autosomal and X-DNA: Autosomal testing allows you to find family across all lines in your family tree. Your autosomal chromosomes carry genetic information from both your parents that's passed down through the generations. Using autosomal testing, AncestryDNA® surveys over 700,000 locations in your DNA, all with a simple saliva sample.The X-chromosome SNP results are often included in Autosomal DNA tests. Both males and females receive an X-chromosome from their mother, but only females receive a second X-chromosome from their father. The X-chromosome has a special path of inheritance patterns and can be useful in significantly narrowing down possible ancestor lines compared to Autosomal DNA.
2. Y-DNA:The Y-Chromosome is one of the 23rd pair of human chromosomes. Only males have a Y-chromosome, because women have two X chromosomes in their 23rd pair. A man's patrilineal ancestry, or male-line ancestry, can be traced using the DNA on his Y chromosome (Y-DNA), because the Y-chromosome is transmitted father to son nearly unchanged. A man's test results are compared to another man's results to determine the time frame in which the two individuals shared a most recent common ancestor, or MRCA, in their direct patrilineal lines.   
3. mtDNA: Mitochondrial DNA is transmitted from mother to child, thus a direct maternal ancestor can be traced using mtDNA. The transmission occurs with relatively rare mutations compared to the genome DNA.