Cytogenetics is a branch of Genetics that is based on the study of chromosomes. Probably the best known example of a genetic condition associated with a chromosomal abnormality is Down's syndrome, where the presence of an extra chromosome 21 (trisomy 21) is associated with a range of abnormal features such as: hypotonia, protruding tongue, single palmer crease, heart defects and intellectual and developmental delay.

The chromosomes of a male with Down's syndrome

The study of Cytogenetics has a number of applications in modern medicine. One of these is prenatal diagnosis, where samples by techniques such as amniocentesis and chorionic villus sampling are cultured and analysed to detect a variety of chromosomal abnormalities such as trisomy 21.

In the post-natal section blood samples are cultured and analysed to detect chromosomal abnormalities. Cytogenetics is an essential tool, for example, in the investigation children with delayed development or of an abnormal appearance. Cytogenetics is also essential in the case of couples with reproductive difficulties such as infertility or recurrent miscarriages. These can be caused by chromosomal abnormalities which may not affect the appearance or health of the person carrying them but may result in miscarriage or the birth of an abnormal child. One type of chromosome abnormality, which may have this effect, is a reciprocal translocation where two chromosomes break and swap segments.

Karyotype of a female with a translocation between the chromosomes 4 and 15.

Cytogenetics is now recognised, by haematologists as an essential aspect of the study of leukaemia, where malignant cells often develop chromosomal abnormalities, a number of which are specific for particular types of leukaemia. Cytogenetics can therefore be useful in the diagnosis, the assessment of prognosis, and the monitoring of treatment in leukaemia.

More Info:
For more information regarding cytogenetics the Association of Clinical Cytogeneticist's web site (https://www.cytogenetics.org.uk/) has a useful links page. Please see also the links page of the Clinical Genetics section of this website.

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Revised 13.04.04 (Alan Clark)
Authorised 23.06.04 (Peter Howard)