Chromosomes (AQA GCSE Biology: Combined Science)

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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-igcse-and-gcse-biology-revision-notes

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

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Lára

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.