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Gene testing involves examining a person's DNA - taken from cells in a sample of
blood or, occasionally, from other body fluids or tissues - for some anomaly
that flags a disease or disorder. The DNA change can be relatively large: a
missing or added piece of a chromosome - even an entire chromosome - that is
visible under a microscope. Or it can be extremely small, as little as one
extra, missing, or altered chemical base. Genes can be overexpressed (too many
copies), inactivated, or lost altogether. Sometimes, pieces of chromosomes
become switched, or transposed, so that a gene ends up in a location where it is
permanently and inappropriately turned on or off.
In addition to studying chromosomes or genes, genetic testing in a broader sense
includes biochemical tests for the presence or absence of key proteins that
signal aberrant genes. |
