Question

how do doctors test for the presence of a brca1 mutation?
a blood sample is tested for the presence of a protein particular to the mutation.
a dna sample is extracted from the nuclei of white blood cells for genetic testing.
breast tissue is biopsied and tested for the presence of a protein on the cell surface.
a dna sample is extracted from epithelial cheek cells in the saliva for genetic testing.
ovarian tissue is biopsied and tested for the presence of the mutation in the cells.

Explanation:

To test for BRCA1 mutation, genetic testing is done. DNA from white blood cell nuclei (as they are nucleated) is used. Testing for protein (options A, C) is incorrect as mutation is in DNA. Cheek cells (option D) might have contamination. Biopsying breast/ovarian tissue (options C, E) is invasive and not standard for initial BRCA1 mutation testing. White blood cell DNA extraction is a common and reliable method for genetic testing of BRCA1 mutation.

Answer:

B. A DNA sample is extracted from the nuclei of white blood cells for genetic testing.