How to Analyse DNA in Genetic Genealogy

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How to Analyse DNA in Genetic Genealogy

DNA has many uses in genealogy, and there are two main ways that DNA is tested in order to create a profile of your genetic make-up. In genealogy, 3 main DNA types are tested and analysed, those DNA types are:

    Autosomal – Distant past, used in ancestrymtDNA – Tests the direct maternal lineY-DNA – Tests male direct paternal line

Two types of test can then be completed on the DNA; STR’s (Short Tandem Repeats), also known as Microsatellites and SNPs (Single-Nucleotide Polymorphism).

STRs are repeating sequences of 2-6 base pairs of DNA. For example, the sequences below:

A T T C C T A _______

_____TCCT________

_TCCT____________

…would have 3 repeats, and by examining several STR loci (locations on a chromosome) and counting the number of repeats, it is possible to create a unique genetic profile of an individual.

STRs are usually considered as “junk DNA”, due to the fact they do not code for protein, and interrupts the DNA’s sequence of genes. The number of times a DNA sequence is repeated for a given STR defines the unique differences between individuals, and because of this, it makes STR’s very useful in forensic studies, and criminal investigation. As an example the FBI tests the genetic profile of individuals using just 13 microsatellites, providing them with a 99.999% level of accuracy.

Y-DNA STRs are commonly used to decipher male lineage, as male descendants will have exactly the same or very similar Y-DNA STR pattern. As a result, it is Y-DNA STRs that are used to determine a male paternal line, and find out whether two individuals are parent and child. Microsatellites can be regarded as a recent past genetic time machine. A huge database of the genetic profiles of individuals is somehow needed in order to take full advantage of the STRs power.

In comparison to STR mutations, SNP mutations are much lower frequency. This makes SNPs much more useful when analysing DNA for the purpose of tracking deep ancestry, and tracking a person’s DNA back thousands of years. As a result it is these SNPs that are used in the DNAme genetic test, as they allow our scientists to compare your Y-DNA, mtDNA and Autosomal DNA with mutations from thousands of years in the past.

SNPs are a DNA sequence variation occurring when a single nucleotide – the DNA is composed of 4 nucleotides only, see the What is DNA? article for more information in the genome differs between members of a species, or paired chromosome in a human. An example of a typical SNP mutation would be:

Ancestral: A C C T

Derived: A G C T

SNPs can also be used as biological markers, and are used to help scientists locate genes that are associated with diseases, and then the potential risk that individual has of contracting that disease. SNPs can also be used to predict a person’s response to drugs, and susceptibility to toxins. As an example, the human tongue’s ability to detect bitterness in food is coded into your DNA, and can be detected using a SNP.

SNPs are typically analysed using once of 2 techniques, either DNA Chips, or by Mass Array Spectrometry:

    Mass Spectrometry is the technique of analysing DNA fragments generated by chain-termination sequencing reactions and then comparing them by mass rather than by size. The mass of each nucleotide is different from the others and this difference is detectable by mass spectrometry. The mass of a mutated sequence of DNA will be different compared to the ancestral one and it is this extremely small change in mass that we are aiming to detect using a Mass Array.
    A DNA chip is a tiny thumbnail-sized tool which is made with thousands of nucleotide patterns attached to the chip in a grid pattern. The attached sequences then act as probes, and tell a researcher whether a DNA sample contains particular DNA sequences and mutations. The results from the DNA chip are then analysed using a powerful computer.