Every year on April 25, America marks National DNA Day to honor both the discovery of DNA’s double-helix structure (published April 25, 1953) and the completion of the Human Genome Project exactly 50 years later.
DNA Day is a good time to be a genealogist, because DNA tests usually go on sale. Here are the announced prices so far:
- AncestryDNA in the US: $69 (normally $99, ends 25 April); in Canada: $79 CAD (ends 30 April); in the UK: £59 (ends 28 April); in Australia: A$129 (not a sale price)
- Living DNA is on sale worldwide, with regional prices as follows: USA: $59 (normally $99); UK: £59 (normally £99); EUROPE: €69 (normally €109)
CANADA: $99 (normally $149); AUSTRALIA: $119 (normally $169); NEW ZEALAND: $119 (normally $169); REST OF WORLD: $99 (normally $149)
- MyHeritage in the US: $59 (ends 28 April)
- 23andMe is offering $30 off their Ancestry + Health test ($169 instead of $199) through 13 May
Fun Facts About DNA
- Every form of life on the planet uses DNA for its genetic code. Some viruses use a similar chemical called RNA, but viruses are not considered to be fully alive.
- Humans have more than 3 billion base pairs (units) of DNA. Estimates vary, but about 90% of it has no known function.
- DNA is made of two strands of chemical building blocks called nucleotides that are twisted together like two strings of beads. While each strand is tightly connected along its own length, the two strands are held to one another with weak, reversible chemical linkages called hydrogen bonds. This diagram shows the two backbones of the helix with the paired nucleotides forming rungs in the middle. The gap along each rung is a hydrogen bond.
- Each strand is “complementary” to the other, meaning that the nucleotide A on one strand will pair with the nucleotide T on the other. Similarly, the nucleotides C and G pair up. Those pairings are called base pairs.
- Base pairing allows DNA to be copied and repaired. If one strand is damaged, the cell can fix it using the pairing rules from the remaining strand. For example, if one strand reads ACCTG, the complement will read TGGAC.
- The order in which the nucleotides are strung together on a strand is a code that tells the cell how to behave. The weak hydrogen bonds can unzip, allowing access to the code inside to turn a gene on, and re-zip to turn it off.
- The “zippability” (not a real word) of DNA also allows molecular biologists to study it. For example, we can use heat to separate the two strands so that we can sequence the DNA itself. Separating the strands this way is called melting (really).
- The famous DNA structure published by Watson and Crick in 1953 is only one of three known conformations (shape variants) of DNA to occur in nature. All three are double helixes, but they differ in how tightly twisted the strands are (A-DNA is more compact than B-DNA) and which direction the helix twists (Z-DNA turns the opposite way from A-DNA and B-DNA). Watson and Crick described B-DNA. This is what A-DNA, B-DNA, and Z-DNA look like viewed from the side and straight down the shaft:
- Human DNA is packaged into enormous sections called chromosomes. The shortest human chromosome, the Y chromosome, is “only” about 57.2 million base pairs long, while the longest (chromosome 1) is nearly 249 million base pairs long. There is also a tiny circular bit of DNA called mitochondrial DNA that is normally 16,569 base pairs long.
- We inherit one set of chromosomes 1–22 from each parent, meaning that we have two copies of each. Those copies should not be confused with the double helix, because each copy is made up of a double helix.
- The final set of chromosomes is called the sex chromosomes, because they determine biological sex. Women have two copies of the X chromosome (one inherited from each parent) while men have one X chromosome (from their mothers) and one Y chromosome (from their fathers).
I could go on and on about DNA all day!