# Human Genome Project

How the Human Genome Project read the three billion letters of human DNA, from cutting and sequencing fragments to assembling the 23 chromosomes\.

By PETE\!

Topic: Human Body & Medicine

[Open the interactive Jig](https://ask.jig.com/j/ULgftING7zla)

## Transcript

### 1. Reading the book of life

From 1990 to 2003, the Human Genome Project brought scientists in six countries together to read about three billion letters of human DNA\. This helix sculpture shows a short stretch of that text\.

### 2. Four letters, two pairs

DNA has two strands twisted into a right\-handed helix\. Its four bases always pair the same way: A with T, and G with C\. Notice the wide and the narrow groove\.

Here A is green, T red, G yellow and C blue\. These colours are a convention, not real colours\.

### 3. Cut, copy and read

No machine could read a whole chromosome at once\. Copies of the DNA were cut into fragments, and Sanger sequencing read each one letter by letter, a few hundred letters at a time\.

### 4. Assemble the overlaps

Because the fragments were cut in different places, their ends overlap\. Computers lined up the matching letters to rebuild one long continuous sequence\.

### 5. Twenty\-three pairs

The genome is packed into 23 pairs of chromosomes\. Chromosome 1 is the largest, about 247 million letters\. Tap a chromosome, or use the slider, to pick one\.

### 6. Finished, then finished again

The 2003 sequence covered about 92 percent of the genome\. Repetitive regions near centromeres and the short arms of five chromosomes stayed dark until the gapless T2T sequence of 2022\.

### 7. Two metres in every cell

Stretched out, the DNA in one human cell is about two metres long\. Any two people share about 99\.9 percent of it, and the project released its data openly for everyone to use\.