Genomics For Dummies

DNA is a molecule made up of two linked strands that wind around each other, to resemble a twisted ladder in a helix-like shape. That’s why DNA is described as a “double helix”.

Each DNA strand is made up of a backbone and a string of letters, called ‘nucleotide bases’. There are four possible bases: A, C, T, and G. The other ‘complementary’ strand will have matching bases (as a rule: A will always pair with T, and G will always pair with C). So even if you only have access to one DNA strand, it is easy to determine the order of the bases on the other strand as it will just be whatever matches the first strand.

A gene is a defined segment of DNA bases that is used to make specific proteins in the body. The DNA bases that ‘encode’ genes are called ‘coding’ DNA.

Human genes vary in size from a few hundred bases to over a million bases, and each DNA molecule in humans will encode 20,000 genes. Some of these genes will correspond to characteristics such as eye color, and diseases such as cystic fibrosis. Differences in DNA segments/ genes between different people are called ‘genetic variants’.

The entire sequence of genes and bases (including those bases that do not correspond specifically to a gene, i.e.: ‘non-coding DNA’ or ‘introns’) are called the ‘genome‘.

Finally, DNA/ the human genome is stored in human cells as chromosomes.

A chromosome is a tightly wound coil of DNA, and the word ‘chromosome’ just refers to this structure. Tightly packing the DNA in this manner allows it to fit inside the nucleus of every tiny cell in the human body. Each cell in the body contains 23 chromosome pairs (so 46 chromosomes in total).

I hope that all made some sense. Next week, we’ll explore perhaps the most important question in this series – what do genes actually do?! See you then 😊