What is a chromosome?

A chromosome is a thread-like structure of tightly coiled DNA and proteins (histones) inside cell nuclei, carrying genetic information as genes.

• Humans: 46 chromosomes in 23 pairs.
• 22 pairs = autosomes; 1 pair = sex chromosomes (XX female, XY male).
• Each chromosome contains hundreds to thousands of genes.
• Abnormalities cause conditions like Down syndrome (extra chromosome 21).

Chromosomes are DNA-protein structures carrying genes inside cell nuclei, with humans having 46 chromosomes in 23 pairs.