MAPPING GENES

One process scientists use to locate genes is called cytogenetic mapping. After breaking open nuclei, scientists fix the chromosomes on a slide, and then stain the chromosomes to see the bands. A complete set of banded chromosomes is also called a karyotype. The banding pattern is unique for each chromosome and allow to pair the chromosomes together and identify abnormalities.

Once the banding has occurred, scientists can take an isolated piece of DNA that is radioactively or fluorescently tagged and allow it to stick to its complement on the other chromosome. This is called probing, or in-situ hybridization, and allows scientists to identify the location of a specific gene on the chromosome.

Besides cytogenetic mapping there is linkage mapping based on the analysis of the co-segregation of genetic markers in pedigree populations.

If scientists do find a gene, but are unsure what it does, they can alter this gene and observe the results in the cell or the organism. They may also compare other genes and look for sequence similarities. If the sequences are similar, then most likely the genes are similiar in their functions. Examining tissue in which the gene is expressed can also give clues about what a gene does.