PRACTICAL 1b

Karyotyping



This is a "dry practical" which can be done in your own time and which illustrates the technique of karyotyping i.e. the visual analysis of chromosomes prepared from a cell just before mitosis when the genetic material of a cell has duplicated and condensed into easily visible structures which can then be segregated into the two daughter cells at cell division. Chemical staining of these mitotic chromosomes produces patterns of bands on each chromosome. The patterns are different and unique for each pair of chromosomes (remember - after DNA replication there are two copies of each chromosome in the cell before cell division). Thus, the different chromosome pairs (there are 23 pairs in all in a diploid human cell) can be distinguished from each other. In this way, gross chromosomal abnormalities (e.g. a missing or extra chromosome or translocation of a piece of one chromosome on to another) can be readily identified in embryonic cells taken by amniocentesis.

The exercises you will carry out were taken with permission fromThe Biology Project, an interactive online resource for learning biology, developed at The University of Arizona. The essential pages concerning karyotyping have been copied locally so that they will load quickly. However, if you wish to follow the links to other parts of the Biology Project for your own interest, then you will be linked directly to the University of Arizona, which could be a little slower.

After you have completed these exercises, you should then link to the Spectral karyotyping pages to see how recent developments in methodology can now allow much smaller chromosomal abnormalities, and hence many more hereditary and acquired disorders (e.g. cancers), to be visualised and diagnosed than was previously possible.

Link to:

 .Karyotyping exercise...... .Spectral karyotyping...... .Practicals Home Page