Chromosomes (AQA GCSE Biology)

Chromosomes: Basics

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

• Chromosomes are made from highly coiled strands of relatively long DNA. Each chromosome is made from one DNA molecule

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

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

• Different species of organisms have different numbers of chromosomes in their nuclei

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

  • Horses have 64 chromosomes in 32 pairs

  • Red blood cells are an exception – they lose their nuclei and therefore have no chromosomes

• Before a cell can divide, its genetic material needs to be doubled. This results in the characteristic ‘X’ shaped chromosomes we see in micrographs of cells preparing to divide

Chromosomes are usually uncoiled, when a cell prepares to divide they fold up into ‘worm-like’ structures that we recognise