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.

Although the mutations listed in the table are clearly deleterious and cause breast cancer in women at very young ages, each of the kindred groups had at least one woman who carried the mutation but lived until age 80 without developing cancer. Name at least two different mechanisms (or variables) that could underlie variation in the expression of a mutant phenotype, and propose an explanation for the incomplete penetrance of this mutation. How do these mechanisms or variables relate to this explanation?

Video transcript

Hey everyone, Let's take a look at this question together, many genetic mutations can increase the risk of developing cancer besides genetic factors which of the following can contribute to cancer development. Well, let's take a look at the following options to try to figure out if any of these contribute to cancer development. Starting off with answer choice A pollutants we have to think whether or not something that is in the air can lead to cancer, which we know that sometimes in the air we have these cancer causing articles that are found within the air and can sometimes lead to lung cancer. So pollutants are definitely a way that can contribute to cancer development. Answer choice B says synthetic chemicals, which we know that those man made chemicals can sometimes contain carcinogens which are harmful to the body and can eventually lead to different types of cancer. So synthetic chemicals are another way that can contribute to cancer development. And then, lastly, an unhealthy lifestyle. We know something like smoking or maybe some unhealthy foods, poor diet and several other factors within our lifestyle that if we do poorly, can also contribute to cancer development. So the best answer choice here is answer choice. D All options are correct because we know that pollutants, synthetic chemicals and an unhealthy lifestyle are always that can contribute to cancer development instead of genetic factors. So, answer choice. D All options are correct is the correct answer. I hope you found this video to be helpful. Thank you and goodbye