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What is a chromosome?

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Quick answer

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.

Key things to understand

  1. Each chromosome is one very long DNA molecule wound around proteins called histones.
  2. Humans have 23 pairs (46 total); one pair (X and Y) is linked to biological sex.
  3. Genes — the instructions for building proteins — are segments along the chromosomes.
  4. Before a cell divides, each chromosome is copied so both new cells get a full set.
  5. Errors in chromosome number or structure can cause genetic conditions.

People also ask

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.