After a discussion of gene technology methods in the preceding chapters, we now turn to a few topics of more immediate medical interest. We will be dealing with different kinds of human diseases that have a genetic component and see how some aspects of these diseases may be examined using bioinformatics tools such as Perl.

Inherited disease and changes in DNA

In Chapter 1 we saw how genetic information flows from DNA to proteins. The sequence of bases in DNA determines the sequence of amino acids in protein and that sequence in turn determines the biological function of the protein. The relationship between genetic information in the form of DNA sequences and biological function in proteins has been demonstrated by numerous experiments carried out in molecular biology laboratories. At the same time it is intriguing to note that this relationship is also elegantly demonstrated in nature. Thus, we know of numerous examples of naturally occurring changes in DNA that have marked effects on the function of the corresponding protein. Such changes often give rise to disease. In discussing this further we need to clarify what types of alterations are observed in DNA. We may distinguish two major categories. First, there are highly local changes, such as point mutations (single nucleotide changes) and addition or deletion of a smaller number of nucleotides. Second, there are large-scale rearrangements of DNA sequences that result from DNA recombination events.