Chromosomes (AQA GCSE Biology): Revision Note

Chromosomes: Basics

• In eukaryotic cells, the nucleus contains thread-like structures called chromosomes

• Chromosomes are made from highly coiled strands of DNA

  • Each chromosome is made from one DNA molecule

• Each chromosome carries a large number of genes

• A gene is a small section of DNA on a chromosome that codes for a specific protein. So a gene is found on a chromosome, in the nucleus

Use this image

• In the body cells, chromosomes are normally found in pairs

  • One chromosome from each pair is inherited from the mother, the other from the father

  • Humans have 46 chromosomes in the nucleus of all their body cells, found in 23 pairs

• Before a cell can divide, its DNA replicates, so each chromosome is copied. The two identical copies (chromatids) stay joined, giving the characteristic X shape often seen in images