In an experiment, scientists changed a single gene in cloned flies of a certain species. These cloned flies lacked th...

Mehran on May 9, 2016

@AnkitM let's break the stimulus down first.

P: Scientists changed a single gene in cloned flies of a certain species.

P: These cloned flies lacked ultraviolet vision even though cloned siblings with unaltered, otherwise identical genes had normal vision.

C: Scientists have shown that flies of this species lacking ultraviolet vision must have some damage to this gene.

This is a Strengthen with Necessary Premise question, so we are looking for an answer choice that not only strengthens the argument, but that is also necessary to this argument.

Let's take a look at (B), "No other gene in the flies in the experiment is required for the formation of the ultraviolet vision cells."

This clearly strengthens the argument by eliminating the possibility that other genes, not accounted for in this experiment, can contribute to ultraviolet vision.

Now let's negate it to make sure that (B) is also necessary to this argument.

The negation of (B) is, "Some other gene in the flies in the experiment is required for the formation of the ultraviolet vision cells."

This destroys the conclusion that "flies of this species lacking ultraviolet vision must have some damage to this gene" because it is now possible that some gene other than the one tested in this experiment is responsible for the formation of ultraviolet vision.

Hope this helps! Please let us know if you have any other questions.