Science
What is A chromosome?
A chromosome is a tightly packaged structure of DNA and protein that carries an organism's genetic information. Humans have 46 chromosomes in most cells — 23 from each parent — organized so that very long DNA strands fit inside the nucleus.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains a chromosome.
Key things to understand
- 1Each chromosome is one very long DNA molecule wound around proteins called histones.
- 2Humans have 23 pairs (46 total); one pair (X and Y) is linked to biological sex.
- 3Genes — the instructions for building proteins — are segments along the chromosomes.
- 4Before a cell divides, each chromosome is copied so both new cells get a full set.
- 5Errors in chromosome number or structure can cause genetic conditions.
Frequently asked questions
- What's the difference between a gene, DNA, and a chromosome?
- DNA is the molecule; a gene is a segment of DNA with instructions for a trait; a chromosome is a long DNA molecule packaged with protein. One chromosome contains many genes.
- Why do humans have 46 chromosomes?
- We inherit 23 from each parent. The number is simply how human genetic information is organized — other species have different counts.
- What are X and Y chromosomes?
- The sex chromosomes: typically two X's are associated with female development and an X and a Y with male development, though biology has exceptions.