The secrets of the X chromosome.
These women are identical twins.
They have the same nose, the same hair color, the same eye color.
But this one is color blind for green light, and this one isn't.
How is that possible?
The answer lies in their genes.
For humans, the genetic information that determines our physical traits is stored in 23 pairs of chromosomes in the nucleus of every cell.
These chromosomes are made up of proteins and long, coiled strands of DNA.
Segments of DNA, called genes, tell the cell to build specific proteins, which control its identity and function.
For every chromosome pair, one comes from each biological parent.
