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•  A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length

Karyotypes are the number and types of chromosomes in a eukaryotic cell – they are determined via a process that involves:

  • Harvesting cells (usually from a foetus or white blood cells of adults)
  • Chemically inducing cell division, then arresting mitosis while the chromosomes are condensed
  • The stage during which mitosis is halted will determine whether chromosomes appear with sister chromatids or not

The chromosomes are stained and photographed to generate a visual profile that is known as a karyogram

  • The chromosomes of an organism are arranged into homologous pairs according to size (with sex chromosomes shown last)




  Organised by Size

  Autosomes vs Heterosomes

  Chromosome Types

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•  Use of karyograms to deduce sex and diagnose Down syndrome in humans

Karyotyping will typically occur prenatally and is used to:

  • Determine the gender of the unborn child (via identification of the sex chromosomes)
  • Test for chromosomal abnormalities (e.g. aneuploidies or translocations)

Down syndrome is a condition whereby the individual has three copies of chromosome 21 (i.e. trisomy 21)

  • It is caused by a non-disjunction event in one of the parental gametes
  • The extra genetic material causes mental and physical delays in the way the child develops

Analysing Karyograms  (click on the diagram to show / hide answer)


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