What are chromosomes and how many do humans have?
The Tiny Librarians
What are chromosomes and how many do humans have?
Deep inside almost every cell in your body, there's an instruction manual for building a YOU. It's written in a chemical alphabet, and the whole thing is packed into a space smaller than a speck of dust. Today we're going to meet the librarians that keep that manual neat and tidy: chromosomes.
First, the instructions themselves. They're written in a long molecule called DNA — a twisty ladder, like a spiral staircase, that holds all the directions for how you grow, what color your eyes are, and a million other things. If you uncoiled the DNA from one of your cells and stretched it out, it would be about two meters long. That's taller than most grown-ups.
