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Dipping a Toe Into the Gene Pool

A Very, Very Basic DNA Discussion

little girl in a kiddie pool with a blow up lifesaver

Egads! Now she wants to talk about Biology!?!?

Who else took Biology in school? Were there fruit flies involved? Yuck. And formaldehyde too, as I recall. This was where I learned about the magical DNA double helix. Before you spend a bunch of money on DNA testing, let's take a brief and not too technical look at what the heck this is all about.

DNA molecule helix

The basic physical and functional unit of heredity is the gene. Genes are made up of DNA molecules. Everything living thing on the planet has DNA (deoxyribonucleic acid) that determines whether you are a dog, a potato, a human, or a fruit fly. Fruit flies are great subjects to learn about DNA because they only have 4 pairs of chromosomes. Three that do traits (appearance, eye color, etc.) and one pair that determines sex. All humans have 23 pairs of chromosomes (46 in total) leading to the brand name 23andMe©, right? Twenty two pairs determine traits, one pair determines sex.

Think about your genetic makeup like a book. Your DNA molecules are organized into paragraphs that are your genes. Those paragraphs of genes make chapters called chromosomes, and then the whole story of your life is called your genome (an organism's complete set of DNA info, whether potato, human, or fly). The human genome has around 25,000 to 30,000 different genes that are distributed over the 23 pairs of chromosomes.

sheep painting itself to change color

Gregor Mendel (1822-1884)is the person who figured out in 1455 why some members of your family have that turned-up nose - inheritance of traits! He was looking for ways to build a better sheep, and worked with peas - smaller, cheaper, less smelly. See this article for more info about Mendel:

DNA is made from 4 molecules called "polynucleotides." Each nucleotide is composed of one of four nitrogen-containing compounds that you will see on illustrations by the letters indicated: (cytosine [C], guanine [G], adenine [A] or thymine [T]), as well as a sugar called deoxyribose, and a phosphate group. The really AMAZING thing is that the DNA from any two people is 99.9% identical!!! Only .1% of all those DNA molecules make us different in appearance.

Okay, so why do we care about DNA? We're trying to do our family trees!

When babies are born, they get DNA from both parents, right? And those parents each got DNA from both of their parents, and so on back for generations. We get 50% from Father and 50% from Mother, who each got 50% from each of their parents. Basically, you can see from the chart below, we get some DNA from 128 people back through 7 generations!

DNA inheritance chart

But the DNA isn't passed in exactly the same way to each new baby, unless you are talking about identical twins. When the DNA helix reproduces itself (as cells do) the ladder splits up the middle. The two halves go courting and, literally (you should excuse the expression), hookup with new halve partners. Those 4 nucleobases (C, G, A and T we saw above)pair up in new DNA molecules. DNA halves from dads pair up with DNA halves from moms when babies are being formed.

DNA molecule

When we do genetic genealogy, we are looking for shared DNA pieces between people to identify who we may be related to. The cold cases we are hearing about being solved are being closed by looking for shared DNA. You can tell by how much DNA samples match up if the tested person is a direct relation (parent, child) or a family member (sibling, cousin, uncle).

Know before you buy the differences in the tests! The autosomal DNA test looks at the 22 pairs of chromosomes (all the trait determiners) found in the cell nucleus. The mitochondrial DNA test examines the cells found outside of the nucleus inside the cell walls (inherited from Mom), and the Y-DNA test examines the sex determining chromosome in the nucleus (inherited from Dad). So, buy a Y-DNA test to give it to a male relative only.

Phew! I hope you are still with me! Hopefully, I have cleared out some of the muddy waters surrounding that DNA test you are going to take. Both the MyHeritage© and Ancestry© sites have great explanations of how all your DNA matches work. You don't have to have this biology memorized!

kids splashing in pool with flotation devices

Come on in to the Gene Pool! The water is fine! Of course, I would be delighted to help you along if you need it. Free peeks at your tree and quotes for any additional work you may want.

If you should wish to dive deeper on your own into genetic genealogy, I would highly recommend the book Genetic Genealogy in Practice by Blaine T. Bettinger and Debbie Parker Wayne in the National Genealogical Society Special Topics Series, available at or booksellers. Great explanations and exercises to help you figure it out.

Thank you for reading, sharing and liking this blog and the Facebook page, @WhoIComeFromGenealogy. I have had some great conversations with some of you about your families already!

Hoping you are keeping cool in these hot summer months!

Yours truly,

Leslie Ryan

Not compensated by any of these links!


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