It seems like you can’t read a newspaper or online news about anything related to medicine (not to mention some novels) without running into terms such as DNA, RNA and protein, all sorts. I thought maybe I could provide a primer, in bite-sized bits, which you could use to follow along. The information I will begin with DNA.
DNA is deoxyribonucleic acid, the material that makes up our genes, and it is composed of nucleotides. Each nucleotide contains a phosphate group (phosphorus and oxygen), a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). They pair up with each other to make a single strand of nucleotides into double stranded DNA: cytosine with guanine, adenine with thymine.
Our DNA contains the genetic instructions for the development and function of all living things. Even some viruses contain DNA. So the main of the DNA in any living thing is the long-term storage of information about what makes that life form what it is, and it is passed down from generation to generation.
A chromosome is the double stranded DNA is encoded with genes. In most cells, humans have 22 pairs of these autosomal chromosomes plus the two sex chromosomes (XX in females and XY in males) for a total of 46.
A gene is a unit of heredity transferred from a parent to offspring, which determines some characteristic of the offspring. Technically, a gene is a distinct sequence of nucleotides forming part of a chromosome.
Two personal notes here: the molecular structure of DNA was identified by James Watson and Francis Crick in 1953; their model-building efforts would not have succeeded without the X ray diffraction studs of Rosalind Franklin. I met James Watson in 1962 when he visited Mount Holyoke College in 1962, the year he and Crick won the Nobel Prize in Medicine. Rosalind Franklin was not included because she had died a few years earlier and the Nobel is never awarded posthumously. I think this is a shame. You can read about Franklin and her life in two books: Rosalind Franklin and DNA and Rosalind Franklin, the Dar Lady of DNA.
There are four types of DNA examined in determining genealogy, which is a currently popular endeavor. I have had my DNA genealogy done twice, one by Ancestry DNA and once by 23 and Me. Both yielded the same results although 23 and Me was a little more specific.
The four types of DNA that are examined are: Y chromosome DNA, mitochondrial DNA, autosomal DNA and X chromosome DNA.
- Y chromosome DNA is passed from father to son, so the women are excluded here. However, there is also mitochondria DNA (the mitochondria is a cell organelle that has its own DNA).
- Mitochondrial DNA is passed from mothers to both genders of her children, but only passed on by females. Males carry their mother’s mitochondrial DNA (mtDNA) but they don’t pass it on.
- Autosomal DNA is the DNA on all the other chromosomes (excluding the Y chromosome in males and mitochondrial DNA). This is a combination of genetic material we get from both our fathers and our mothers.
- X chromosome DNA. The X chromosome is a part of the 23 sets used for autosomal testing, but the inheritance is different for males and females. Males only inherit an X chromosome from their mother (and a Y from their father which makes them male), but women inherit an X from both of their parents. The X chromosome has some special characteristics that can be analyzed separately from the other autosomes.
As for my results, I learned that in addition to being of eastern and western European stock (my grandparents were French and Polish) as well as English stock (other grandparents), I am 13% Irish. I never knew that!
There are also companies that will test your maternal lineage and your personal evolutionary history, if you want to delve into your ancient maternal lineage and discover your origins from thousands of years ago. I might try this!
My next ‘genetics’ post will be on RNA.