Volumes and recipes

About this video

One set of human DNA is about 3 billion letters long. A cell can't keep that as one loose thread, so how is it organised, and where are the instructions for something like the colour of your eyes? This video shows it step by step.

In the nucleus, DNA is split into separate pieces, and each is packed tightly into a chromosome, a thread-like bundle of DNA. A human body cell normally has 46 chromosomes, in 23 pairs. You got one chromosome of each pair from your mother and one from your father, so you carry two versions of almost every instruction. Twenty-two pairs look the same in men and women; in the 23rd, women usually have two X chromosomes and men an X and a Y.

A gene is a stretch of DNA that carries the instructions for one job, usually for making one protein. Humans have about 20,000 genes that make proteins. All of your DNA together is your genome. If the genome is a library, the chromosomes are its volumes, the genes are the recipes, and the bases A, T, C and G are the letters.

Most traits don't have a single gene. Several genes shape eye colour, and more than 700 gene variants affecting height have been found, each with a small effect. This video goes with the lesson Genes and Chromosomes in Biology Level 1 on Knaph.

Transcript

1. 0:00One set of human DNA is about 3 billion letters long. How does a cell keep it in order?
2. 0:08It is split into pieces, each packed tightly into a chromosome. A human body cell has 46 chromosomes, in 23 pairs. One of each pair came from your mother, one from your father.
3. 0:24Twenty-two pairs look the same in men and women. The 23rd pair differs. Women usually have two X chromosomes, men an X and a Y.
4. 0:36Along each chromosome sit genes. A gene is a stretch of DNA with the instructions for one job, usually for making one protein. Humans have about 20,000 of them.
5. 0:52Think of a library. The genome is the library, chromosomes are its volumes, genes are the recipes, and the bases are the letters.
6. 1:06Most traits don't have just one gene. Several genes shape eye colour. More than 700 gene variants affect height, each a little.
7. 1:20Two sets of recipes, one from each parent, in almost every cell.