DNA Definitions

DNA And Our Irish Roots


Subcellular structures in the cell nucleus discovered in 1842 by Karl Wilhelm von Nägeli and named chromosomes in the late 1800s. However, their role in cell division and inheritance only became clear in the early 1900s. Humans carry 23 pairs of chromosomes, 22 pairs known as autosomes and the 23rd pair as the sex chromosomes, XX for a girl and XY for a boy. The chromosomes determine everything about the individual from eye colour to a predisposition for many illnesses. Only one of each pair of chromosomes is passed onto the child. The critical heritable constituent of the chromosomes is DNA or DeoxyriboNucleic Acid. Because the Y-chromosome is inextricably linked with male inheritance it can be very useful for tracing the family surname. However it can open up forgotten family secrets, see Y-chromosome and Father's Ancestral Line for more information.

DNA - DeoxyriboNucleic Acid

Although DNA was known about in the 1800s it wasn't until 1944 that it was determined to be the genetic material passed on in chromosomes from one generation to the next for almost all living things; microbes, plants and animals (some viruses use RNA).

Structure of DNA

The structure of DNA with it's double helix and four bases, Adenine, Cytosine, Guanine and Thymine was announced in 1953 by Francis Crick and James Watson. It's like a giant spiral staircase with the steps consisting of the base pairs A-T and C-G. It is the sequence of these base pairs that makes up the genes that define the structure and development of every human. If you're interested in finding out more about the discovery and structure of DNA and the other scientists involved we would recommend James Watson's book "The Double Helix".

The Human Genome Project - HGP

After years of planning this project began in 1990. Its aim was to sequence the base pairs of all human DNA and was completed by 2003.

DNA Testing

For the purpose of tracing heritage it is only necessary to target SNPs (single-nucleotide polymorphism). These are differences in the DNA sequences that lead to genetic variation, so the more SNPs two people have in common the closer they are related. There are over 10 million SNPs in human DNA but DNA testing for heritage only tests for a subset of these, enough to determine ancestry and give a guide to ethnicity.

Full DNA sequencing

The HGP cost billions but the cost of a full DNA sequence for an individual is coming down all the time and it may not be too long before commercial companies can offer full sequencing for less than $1000. However, this won't be necessary for researching your Irish Roots!

Mitochondrial DNA

See Mitochondrial DNA and Mother's Ancestral Line.

DNA And Your Irish Roots

Learn more here: Irish DNA