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This drawing
arranges all exons, introns, repeats and other sequences in
left to right order. Note the regions of approximate vertical
homology. Now pass your mouse over the drawing and note how
the exons that code for protein only constitute a small portion
of the gene.
In 1990, through genetic
linkage studies, a gene(BRCA1) was localized on chromosome 17
at band q21 that predisposes to a significant proportion of
early-onset breast cancer. Later studies found BRCA1 increased
susceptibility for ovarian cancer as well as breast cancer.
A study of 214 families
linked to 17q21 the cumulative
risk for breast cancer associated with BRAC1 to be about
59% by age 50 and 87 % by age 70.
Another gene (BRCA2) has
been implicated in hereditary breast cancer. This gene has been
localized to a region on chromosome 13q12-q13.
Several families linked
to BRCA2 show breast cancer in women as well as men, whereas
no breast cancers in men have yet been observed in families
linked to BRCA1.
The p53 gene also has
been linked to breast cancer. This gene is a tumor suppresser
gene which normally acts as a transcription factor that regulates
the expression of other genes and has been mapped to chromosome
17p13.
A variety of different
types of mutations in this gene have been found.
The OMIM
morbidity map shows this and other cancer genes. Genes implicated
in the cancer process are called oncogenes.
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