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A gene is the basic physical and functional unit of heredity. Genes are made up of DNA. Some genes act as instructions to make molecules called proteins. However, many genes do not code for proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases. The Human Genome Project estimated that humans have between 20,000 and 25,000 genes.

Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people. Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features.

What are BRCA1 and BRCA2?

BRCA1 and BRCA2 are human genes that produce tumor suppressor proteins. These proteins help repair damaged DNA and, therefore, play a role in ensuring the stability of each cell’s genetic material. When either of these genes is mutated or altered, such that its protein product is not made or does not function correctly, DNA damage may not be repaired properly. As a result, cells are more likely to develop additional genetic alterations that can lead to cancer.

Specific inherited mutations in BRCA1 and BRCA2 most notably increase the risk of female breast and ovarian cancers, but they have also been associated with increased risks of several additional types of cancer. People who have inherited mutations in BRCA1 and BRCA2 tend to develop breast and ovarian cancers at younger ages than people who do not have these mutations.

A harmful BRCA1 or BRCA2 mutation can be inherited from a person’s mother or father. Each child of a parent who carries a mutation in one of these genes has a 50% chance (or 1 chance in 2) of inheriting the mutation. The effects of mutations in BRCA1 and BRCA2 are seen even when a person’s second copy of the gene is normal.

Sources:

  1. Courtesy of NLM Genetics Home Reference: What is a gene, National Institute of Health: https://ghr.nlm.nih.gov/primer/basics/gene, accessed on August 14th, 2020.
  2. Courtesy of NIH National Cancer Institute: BRCA Mutations: Cancer Risk and Genetic Testing: https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet#how-much-does-having-a-brca1-or-brca2-gene-mutation-increase-a-womans-risk-of-breast-and-ovarian-cancer, accessed on August 14th, 2020.

Additional Readings:

  1. The Basics on Genes and Genetic Disorders, TeensHealth https://kidshealth.org/en/teens/genes-genetic-disorders.html
  2. What is a gene, National Institute of Health, https://ghr.nlm.nih.gov/primer/basics/gene

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