Understanding:
• 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)
Karyograms
Feature:
Unorganised
Organised by Size
Autosomes vs Heterosomes
Chromosome Types
Application:
• 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)
