Each cell (except for sperm and egg cells) have two copies of each chromosome in its nucleus. This provides cells with a backup in case one gene copy becomes mutated. This is especially important for "tumor suppressor genes" such as BRCA1 and BRCA2 that normally play a critical role in preventing cells from becoming cancerous. (Joyce Seldon)

Adventures in Genetic Testing

Each cell (except for sperm and egg cells) have two copies of each chromosome in its nucleus. This provides cells with a backup in case one gene copy becomes mutated. This is especially important for "tumor suppressor genes" such as BRCA1 and BRCA2 that normally play a critical role in preventing cells from becoming cancerous.

Credit: Joyce Seldon