All That Genetic Stuff: DNA

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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.

 dna

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.

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31 thoughts on “All That Genetic Stuff: DNA

  1. Now I feel very educated! Incidentally, Crick was born in my home town of Northampton, specifically a place called Weston Favell which was part of my beat when I was in the police. When he and Watson made their great discovery, they immediately went to The Eagle public house in Cambridge and became very drunk. The Eagle is one of my favourite watering holes and is immortalised in my books as The Albatross! There is also a super statue dedicated to Crick on Abington Street in Northampton, celebrating the discovery of DNA. I look forward to learning about RNA – I confess to knowing nothing at all about it!

    • Haven’t written that one yet, but it’s coming. When Watson came to give a talk at my college (all women) we were warned he was a womanizer and to be careful. Eagle to Albatross – nice switch! I’m still pissed about Rosalind Franklin. I studied her X ray diffraction patterns- she was technically brilliant and surmised the DNA structure before they did.

  2. I spent a long time researching genetics and inherited DNA haplogroups and mitochondrial and so on for my novel My Fathers and Other Liars where it features a lot. Boy did my brain melt. Wish I’d had you alongside! As for the disgraceful way Watson and Crick tried to sideline Franklin and her boss, well not their finish hour. But then Watson has a bit of a track record with his flirtations with eugenics so it’s just another example that geniuses can also be arseholes….!

  3. I grew up in a unit of 4 – 2xparents, 2xchildren – no other relatives around or known. I’ve spent more than 20 years researching my genealogy and now have a family tree of more than 1,800 people. Of these I have discovered cousins and corresponded with many. Thanks to DNA testing (FTDNA I h)ave just confirmed another 4xgt grandparents. It is nice to know one is not alone in the world!

  4. Thanks, Noelle. You made me realize something I’d never thought of regarding inheritance, that is, that only a male inherits a Y chromosome from his parents, and only, of course, from his father. And that naturally means that a male only inherits an X-chromosome from his mother, whereas a female gets an X chromosome from both parents. All of which would make traits that occur on X and Y chromosomes very interesting to consider from an evolutionary or inheritance standpoint.

  5. Thanks for this refresher. I used to work for a biotechnology company and this was very interesting to read. I’d forgotten so much of this from what I learned in school and I miss this subject so much. I’ll have to share this with my girls, it’ll be an easy way to explain this to them. I’m looking forward to your next post on RNA. 😉

  6. Wonderfully explained in a easily comprehended way, thanks Noelle. I was actually (wrongfully I believe!) dismissed from my last job as a school librarian. When asked “Where is the Principal?” I said “He’s not here. He stayed home to look after 23 of his chromosomes!”

  7. Well done and very clear. Thanks for drafting and posting a nice primer for many and a wonderful refresher for me. As I’ve said before, I LOVE posts like these!

    Do you plan to include something about genetic testing for health vulnerabilities? Too many people are unaware that, depending on “environmental” influences, genes are not always expressed, but if you have a family history, I believe it’s good to get out in front of things.

    I, too, wish they’d include scientists who died in Nobel awards – they could include a “posthumous” category that does not come with money attached, so no hassles with relatives, etc. if they would. Maybe even an “honorary” category, which would honor the contributions of many, I’m sure.
    xx,
    mgh
    (Madelyn Griffith-Haynie – ADDandSoMuchMORE dot com)
    ADD Coach Training Field founder; ADD Coaching co-founder
    “It takes a village to educate a world!”

  8. Thanks for the refresher course, Noelle! I learned all of this a couple centuries ago in nursing school but didn’t realize how much I’d forgotten. Science fascinates me … 🙂

  9. My two cousins both male died aged 13 from a genetic illness called Hunters Syndrome there is a bigger Latin name but I can’t remember it, their sister doesn’t have it but she did survive childhood leukaemia I always wondered if the conditions were genetically linked?

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