Breast cancer is the most common cancer that affects women in the United States. There are at least two majors genes (BRCA1 and BRCA2) that when they mutate can cause breast cancer. These genes can be passed from parent to child, increasing the risk of developing cancer in those child that have parent carrying these genes. BRCA1 and BRCA2 genes are located on chromosome 17 and chromosome 13 respectively. There is a 90% chance of developing breast cancer for a woman that has these mutated genes. In contrast, men carrying BRCA1 have no risk to develop breast cancer, but those carrying BRCA2 genes have high risk. It is important to note that mutations in these genes can be passed on to children by either parent. A man with a mutation is just as likely to pass this gene to his children as a woman with a mutation. Hereditary cancer occurs at young age, for instance a woman in her 20's with breast cancer is more likely to have hereditary type of cancer that a woman in her 50's. (http:www.familycancer.org/FamHist.stm)
BRCA1 and BRCA2 are tumor suppressor genes, these genes also called "Anti- Oncogenes" which normally are involved in regulating cell growth, the proteins inhibit the proliferation of cell, which is crucial for the normal cell development and differentiation. (Britanica on line).
Since the discovery of the BRCA1 and BRCA2 in 1994 and 1995 about 80% of the women who inherit mutated forms of these genes will develop breast cancer in their lifetime, usually at relatively early age and woman with BRCA1 mutations have a high risk of developing ovarian cancer as well.
Kudson in 1971 proposed a two-mutation theory of cancer causation. His theory stated that all cancer are of two kind, hereditary and sporadic In the case of hereditary cancer, at the time of fertilization, the zygote (the fertilized egg) receives a imperfect copy of a gene (mutation). Subsequently, each cell that develops from the fertilized egg will receive this mutated gene. He states that for a cancer to manifest, two mutations must occurs. In hereditary cancers, the person inherit one mutant gene. The second mutation occurs as result of a mitotic error during the many cell division that occurs in the person's lifetime. In sporadic cases both mutation occur in the person's lifetime. In sporadic cases both mutation occurs after fertilization an are acquired much later in life. From this Kudson conclude that hereditary cancers manifest at younger age and there is a higher incidence of multiple tumors, where sporadic cancers occur late in the life and usually only a single tumor occurs. The principal causes of cancer appears to be environmental agents. A good example of this is skin cancer. The condition has increased among fair skinned people who expose themselves to too much sunshine, while being very uncommon among dark skinned races (knudson 1971, cited in Ormiston, 1995). Therefore, most genetic alteration are acquired through our life time from environmental...