#22 - After a hepadnavirus inserts itself into a chromosome

[lll7]

Can someone please help me out with this one?

Why is A wrong and C right?

[Emily Haney-Caron]

Hi lll7,

I noticed you posted a few questions about this exam, which is great! I'm glad to see you're really working to figure out why you got questions wrong.

I want to make sure you also get the most out of this process, though, which means giving you a chance to think through the questions on your own and also making sure our answers are as tailored to you as possible. To do that, it really helps a lot if you:
1. explain how you understood the stimulus (what portions were premises? what was the conclusion?)
2. explain what you think of the logic of the argument (does the conclusion flow logically from the premises? if no, why not?)
3. tell us what type of question this is based on the question stem
4. identify what your prephrase was (if you didn't have one when you first did the question, that's okay! Now's a great time to go back and come up with one)
5. explain why you chose the answer you did and why you think it is correct now

Once you provide that info, you might find that you've answered your own question and caught your mistake. If so, great! If not, that's why we're here; post information related to each of the above five areas I've identified, and we can make sure the answer we give directly addresses the thing that tripped you up. This will allow you to get the most out of the studying process, because it will help you really think through questions thoroughly on your own (a great way to learn!) and then help us figure out how to help get you to the right answer.

I'll post this on a couple of other questions you asked about this exam, as well, so you have the list right there on each question. Once you answer with that info, we'll give a detailed answer to get you back on the right track.

[TigerJin]

I chose E over c. C just did not appear relevant at all. I chose E thinking, that if the virus doesn't kill off the animals, then that means the virus did not have to be of recent origin (it would be possibly for the infected animal to have descendants.)

How is C relevant, let alone strengthen the argument?

[Adam Tyson]

Think about what the author must be assuming here, Tiger. He seems to think that the virus must have inserted itself into this bird's ancestors back before the two species diverged, right? That's how he gets the idea that the virus is that old, predating the divergence. Why does he think this? Because the virus is found in the same exact spot in both birds.

Now, we don't normally use anything like a "negation technique" on strengthen questions, but imagine for a moment what would happen if the virus always inserted itself into the exact same spot in every bird. That would wreck this argument! The virus could be just a week old, having inserted itself into both birds that recently. The fact that it was found in the same place in both would not matter at all.

If it always inserts itself at a random spot, that at least reduces the chances of any two birds having it in the same spot. To find it in two related birds in the same spot would be a heck of a coincidence. It would make it a little bit more likely that they got it there from a common ancestor! It doesn't prove it, of course - random insertion could of course lead to two birds having it in the same place, especially if there aren't that many places to put it - but it does help, at least a little. That's all we need on a strengthen question, just a little help.

E is no help at all. So the presence of the virus affects survival - so what? Affects it positively or negatively? What does that do to the conclusion about how old the virus is? Since E is no help to our conclusion, we have to reject it. We might not like C very much, but it's better than all the other answers, and so that has to be it.

Keep at it!

[TigerJin]

OH! I didn't think of it like that! Thanks!

[sc01]

Adam, I completely understand your explanation for why C is correct. When I did my corrections, I was able to grasp that C removes any idea that the birds got the virus independently (kind of like a defender assumption). However, I chose A on the exam and I am still unable to understand why it is not a strengthener. Can you please explain? Thanks!

[Adam Tyson]

Good question, sc01! I'm glad the prior explanation helped, and I see why you like answer A. It gets us thinking about whether maybe the virus, inserted into these birds' ancestors so long ago, may have actually contributed to their having diverged, right? The problems are twofold:

1) Answer A says that the virus can influence a species diverging into two, but it doesn't tell us whether that influence is positive of negative. Does it make it more or less likely? Be careful not to make any assumptions about that! A negative influence might hurt here. A positive influence might help a little, maybe, by opening up that possibility - maybe that happened here.

2) Remember what we are told to do in the instructions - pick the best answer. A, looked at through squinted eyes and giving it a little help, might strengthen a little bit. But answer C helps so much more! You have to pick the one that does the most to strengthen, not just one that might strengthen some. C is stronger, so C is better, and A has to be crossed out.

Think again about what the influence is, and consider what bias you may have brought to that answer. The authors may have laid a nice little trap just for you! Next time, you won't fall into it so easily.

Keep at it!

[freddythepup]

Hi,
I read your explanation but I'm still not convinced C is the correct answer. The reason why it doesn't work in my opinion is I don't get why inserting it in a random spot is better than always being the same spot. Why would it matter if it just so happened that the virus always was inserted into the same spot for different birds? Why would that make it more likely that the virus was more recent than 25 million years ago? can you please explain? thanks!

[deck1134]

I had to do a double take on this one. The (C) answer makes sense, sure, but it sure is not normal! I almost had to do a "negation technique" to see how it would affect the answer choice. Wild!

[LSAT2018]

He seems to think that the virus must have inserted itself into this bird's ancestors back before the two species diverged, right? That's how he gets the idea that the virus is that old, predating the divergence. Why does he think this? Because the virus is found in the same exact spot in both birds.

Can I have a extended explanation for this? Where does it indicate that it was BEFORE the species divereged? It seems like I am not understanding this stimulus at all