-A curious adult from Nevada
December 13, 2017
Your DNA has the instructions for making you. One complete set of instructions is called a genome.
These instructions are written in “letters” called base pairs. A human genome has around 3 billion base pairs.
The reason you sometimes see the 6 billion number has to do with how your DNA is stored in your body.
Your body is made up of trillions of cells. Each of these cells has two copies of your genome.
Sperm and Eggs Have One Genome
Are you still wondering why sperm and eggs only have one genome copy? Well, maybe it’s helpful to talk about the types of cells in the human body.
In general, there are two categories of cells. Most of the cells in our body are called somatic cells. Somatic cells have two genome copies.
Egg and sperm cells make a different category called germ cells. Germ cells start off with two genome copies. Eventually they divide into two cells with one genome copy each. This process is called meiosis.
Not All Cells Have Genomes!
So we know that the cells in our body have two genomes and germ cells have one genome. Every genome is housed in an area of the cell called the nucleus. But there’s more to it.
Not all of the cells in our body has copies of the genome. Red blood cells, and some cells in our skin, hair, and nails don’t have any genomes In their nuclei. These cells start off with genomes in order to develop properly, but then destroy their nuclei later on.