The table in this problem summarizes some of the data that have been collected on mutations in the BRCA1 tumor-suppressor gene in families with a high incidence of both early-onset breast cancer and ovarian cancer.

Predisposing Mutations in BRCA1
Kindred    Codon    Nucleotide     Coding Effect     Frequency in
                               Change                                    Control
                                                                                Chromosomes    
 1901          24           -11 bp          Frameshift           0/180
                                                       or splice
 2082        1313         C→T           Gln→Stop            0/170
 1910        1756         Extra C        Frameshift           0/162
 2099        1775         T→G            Met→Arg            0/120
 2035         NA*          ?                  Loss of                NA*
                                                       transcript                                      _
Source: (1994). Science 266:66–71. © AAAS.

Note the coding effect of the mutation found in kindred group 2082. This results from a single base-pair substitution. Draw the normal double-stranded DNA sequence for this codon (with the 5' and 3' ends labeled), and show the sequence of events that generated this mutation, assuming that it resulted from an uncorrected mismatch event during DNA replication.

Video transcript

Hey everyone, let's take a look at this question together. Which of the following statements about B. R. C. A. Gene mutations is true. So let's recall what we've learned about that B. R. C. A. Gene mutation. To try to figure out which of these following statements are true. So what are some things we know about that B. R. C. A. Gene mutation? So we know that having that gene mutation does not mean that the patient has breast or ovarian cancer, but it means that they have a higher risk or cancer compared to those who don't have that mutation in the B. R. C. A. Gene. And we also know that when we conduct that test to see if there are mutations in that B. R. C. A gene, that negative test outcome does not mean you are safe. And what this means is even though the test result comes back negative, it is possible that that mutation is not detectable. So, a negative test doesn't necessarily mean that you are not at risk because of that possibility that that gene mutation is not detectable. So it is important to investigate the family history to give an accurate diagnosis, which means that answer choice C. Is a true statement regarding that B. R. C. A. G mutation. Because in answer choice A it says all women with the gene mutation have breast cancer. And answer choice. B says all women with that mutation have ovarian cancer, which we know is not true because if you have that gene mutation, it does not mean that you have breast or ovarian cancer. It just implies that there is that higher risk of having that breast or ovarian cancer. So answer choice is A and B. Are not true statements. And then answer choice D. Says that the neck gene test means that a woman is safe from breast cancer, which we know is also not true because that negative test does not mean you are safe. It could mean that the gene is undetectable by the test, which is why you should investigate the family history of breast cancer to see if you have that higher risk. So answer choice C is a true statement and is the correct answer to this question. I hope you found this video to be helpful. Thank you and goodbye.