3. One of the most common genes involved in cancer is BRCAL, BRCA1 is largely on

Question

3. One of the most common genes involved in cancer is BRCAL, BRCA1 is largely only expressed in breast tissues. Mutations in BRCAl make a cell less effective at repairing DNA. (a) If you sequenced somatic cells from an individual who has the BRCA1 mutation and someone is wild-type, how might the rate of new mutations compare? that (b) What about if you sequenced germ cells? (c) Would you expect a kid of a parent with a cancer-causing mutation in BRCA1 to have more muta- tions compared to their parent than a kid with a wild-type parent? (d) Would you use DNAseq or RNAseq to test this hypothesis? Why? (e) Women who have the BRCAl mutation often end up getting a mutation in other genes that lead to mitosis no longer working properly. Most commonly, the cell is no longer able to stop mitosis. Why would that lead to a tumor? (f) The BRCA1 mutation is particularly common in the Ashkenazi Jewish population, which we know has a history of inbreeding. How could inbreeding make a mutation common?

Explanation / Answer

a. BRCA1 is a tumor suppressor gene involved in DNA repair. This protein combines with other tumor suppressors, DNA damage sensors and also with signal transducers to form a larger unit of protein known as BRCA1 associated genome surveillance complex (BASC). This BASC binds to RNA polymerase II and plays role in transcription, repair of DNA double bonds and also in recombination. Hence individual having mutation in BRCA1 of somatic cell has more mutation rate compared to the individual having wild type copy.

b. Germline mutation of BRCA1 has been found in 9% of the cases. Germline mutation leads to higher rate of mutation compared to somatic cell mutation. It is because mutation in germline cells spread to all cell types of the body and hence leads to mutation in every cell types.

c. There is 50% of chances that kid develops mutations in BRCA1 if their parents have mutation in BRCA1. As it is inherited mutation, kid develops more mutation than their parents compared to the kid with wild type parent.

d. DNA sequencing is used to test whether the copy of BRCA1 is normal or abnormal. Because DNA sequencing provide details about how mutation is progressing as it is involved in DNA repair mechanism. If DNA repair mechanism is impaired due to defect copy of BRCA1 which leads to higher incidence of mutation which can be traced in detail using DNA sequencing.

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