Extended banding chromosome studies Extended banding or high resolution chromosome studies means that the chromosomes are studied at a higher resolution than the standard chromosome analysis mentioned above. The chromosomes are prepared in such a way that they are a little longer, so that more bands can be seen. This allows you to see smaller pieces of the chromosome, so that you could identify smaller structural chromosome abnormalities not visible on a routine analysis. It is also used to identify structurally-abnormal chromosomes. This DNA is called a probe .
Probes can find matching segments of DNA when added to cells under certain conditions.
For example, if a baby is suspected of having trisomy 21 Down syndrome and an amniocentesis is done on the pregnancy, a FISH study can be performed on the cells found in the amniotic fluid. A FISH study does not replace a chromosome study, but is done in addition to a standard chromosome study, depending on the birth defect in question. Click here to view the Online Resources page of this Web. Copyright 2000 Lucile Packard Children's Hospital. All rights reserved.