Q. 30

[admin]

There are some counter arguments regarding your answer choice. The two I mention here stem from your correct definition of sex-linked dominant (which, for the interest of others, would not be tested on the MCAT). To begin with, if you already know that definition then you also know that sex-linked dominant diseases are exceedingly rare. But note that the passage is describing one of the most common glandular diseases affecting millions of people. The other point is, if this were simply a sex-linked disease then it would be quite odd that it only differentially affects women between the ages of 20 and 60 rather than the difference being for a lifetime (like a more commonly known sex-linked recessive disease: hemophilia).

[admin]

We have to be careful not to confound important points that you are making. To begin with, most cancers are environmental (ie, smoking, diet related, UV radiation, viral, etc). The environment in turn affects genes to result in abnormal cell growth. But this is not what is meant by a genetic disease which is one that is passed on in the genes. Genes can predispose to cancer and, occasionally, be the source; however, in general, cancer is environmental and that includes testicular and especially breast cancer. The genetic aspect of breast cancer (women born with the gene that has an extremely high rate of developing the disease) occurs in less than 5% of women with breast cancer.

And yes, you probably are thinking too much! This is first year college biology! And, in fact, most of it is advanced high school material. For the MCAT, sex-linked means recessive. Why would they have you memorize obscure genetic conditions when they can trick you regarding "common" knowledge for first year students? In general, "keep it simple" would be good advice for this test.

[admin]

bump

[davis.32517441]

Although the disease in this passage may in fact not be sex linked, and it may be true that it is rare for a sex linked disease to be more common in females, the logic behind B is incorrect.

Because it is only "exceedingly rare", means that there are cases where sex linked diseases are in fact more common in females (with a dominate allele as OP stated), thus you cannot eliminate the possibility of a disease being sex linked only on the bases of it being more common in females.

Why would the correct definition of a sex-linked disease not be tested on the MCAT? Sorry to contend, but I wouldn't want this problem to go unnoticed for test takers.

Thanks for your time.