GCSEScienceAQACombined Science: TrilogyBiologyRevision NotesCell BiologyCell DivisionChromosomes

Chromosomes (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Exam code: 8464

Lára Marie McIvor

Written by: Lára Marie McIvor

Reviewed by: Dr Natalie Lawrence

Updated on

AQA Combined Science: Trilogy: BiologyAQA Biology

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

Diagram showing the organisation of genetic material in a cell. The nucleus contains chromosomes. Each chromosome consists of a long strand of DNA wrapped around proteins, and DNA has a double-helix structure.

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

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Author
Reviewer
Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Content Creator

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.

Dr Natalie Lawrence

Reviewer: Dr Natalie Lawrence

Expertise: Content Writer

Natalie has a MCantab, Masters and PhD from the University of Cambridge and has tutored biosciences for 14 years. She has written two internationally-published nonfiction books, produced articles for academic journals and magazines, and spoken for TEDX and radio.