results from a large DNA rearrangement, this anomaly can usually be detected by 

 alterations in the physical map of the region or even by examination of the 

 chromosome. The location of these alterations pinpoints the site of the gene. 



To identify — without a map — the gene responsible for a specific disease, is analogous 

 to finding a needle in a haystack. Finding the gene is even more difficult, because no 

 matter how close one gets, the gene still looks like just another piece of hay. However, 

 maps make finding genes much easier. They tell where to look in the haystack. The 

 finer the map, the fewer the pieces of hay one has to test to see which is the gene of 

 interest. 



normal gene 

 30,000 bp 



single base 

 change 



deletion 



insertion 



translocation 



Fig. 17. Possible DNA 

 abnormalities that can 

 produce an inherited defect. 



137 



