TBR Biology Chapter 10 Passage 2 #11

[Jengreef]

The above are the question and answer given by TBR. I'm having difficulty understanding what constitutes a correct "cut" as defined by the book because there are a few cuts I don't agree with. For instance Bgl II makes a cut at 7kb and 2kb, but from what I can tell, choice C has Bgl II making a cut at 5 and 4 kb fragments. The solution disagrees and states that Bgl II made the correct cut in C. But if it made the correct cut in C, then all cuts on all choices are also correct. What makes one choice better than the other? Another problem is the answer states that Pst I made an incorrect cut in choice C, but I think C has the correct cut from Pst I, giving fragments of 1, 2, and 6 kb in size. Nothing about the explanation seems to align with how I understand these digests to come out. Maybe I'm misunderstanding some key element, but I'm not getting it from the solutions. Help would be much appreciated.

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[Jepstein30]

The above are the question and answer given by TBR. I'm having difficulty understanding what constitutes a correct "cut" as defined by the book because there are a few cuts I don't agree with. For instance Bgl II makes a cut at 7kb and 2kb, but from what I can tell, choice C has Bgl II making a cut at 5 and 4 kb fragments. The solution disagrees and states that Bgl II made the correct cut in C. But if it made the correct cut in C, then all cuts on all choices are also correct. What makes one choice better than the other? Another problem is the answer states that Pst I made an incorrect cut in choice C, but I think C has the correct cut from Pst I, giving fragments of 1, 2, and 6 kb in size. Nothing about the explanation seems to align with how I understand these digests to come out. Maybe I'm misunderstanding some key element, but I'm not getting it from the solutions. Help would be much appreciated.

They're wrong on both accounts... nice catch.

 

[skeptastic]

I know that this thread is extremely old, but I saw no purpose in creating a new thread to ask the exact same question. Can @BerkReviewTeach please help with this one? The answer explanation doesn't help one understand this problem at all and when you try to use the logic presented in the answer explanations for one part, that same logic doesn't work with other parts of the problem. I mulled over this one for at last 30-40 minutes, and finally have just let it go and figured I'd check SDN to see if anyone else had issues with this problem.

 

[BerkReviewTeach]

Blast from the past!

I believe the best approach is to go choice by choice and map out the masses. I agree with the first paragraph of the explanation that confirming the total mass as 9 for each column helps. But it appears there is an error in paragraph 2 with BhI II and choice C. So let's get the correct answer by a different route, and then figure out where the error in the book lies.

For A: From the drawing, BhI II would give masses of 1 and 8, which does not match the first column to the right of the ladder. A is looking bad.

For B: From the drawing,BhI II would give masses of 7 and 2, Pst I would give masses of 1, 6, and 2, and Eco RI would give masses of 4 and 5. This matches what we see in the first three columns on the left, after the ladder. B is looking good.

For C: From the drawing,BhI II would give masses of 4 and 5, Pst I would give masses of 2, 6, and 1, and Eco RI would give masses of 4 and 5. Although Eco R1 and Pst I are correct, BhI II gives the wrong mass fragments. C is looking bad.

For D: From the drawing,BhI II would give masses of 5 and 4, Pst I would give masses of 2, 6, and 1, and Eco RI would give masses of 2 and 7. Although Eco R1 is correct, BhI II and Pst I give the wrong mass fragments. D is looking bad.

I believe that is a good and systematic manner to approach this question.

As for the explanation in the book, I believe there is an error in the analysis of BhI II when it says it is valid for choices B and C. I believe it is only correct for choice B, as the OP stated.

Unfortunately, the error has not been corrected in the latest printing of the book and looks to date back at least ten years. I'm hopeful the upcoming print run will address this error, and many others. But to be honest, BR has lost some key members of the team over the past three months, so time will tell.

 

[BerkReviewTeach]

Okay, so it was bothering me how a typo from a 2011 book posted in 2013 could be asked now, and my first assumption was that it was an old printing of the biology book. I cannot apologize enough for the fact that this typo remains in the current edition and has been in that book for so long.

 

[BerkReviewTeach]

The 2022 Biology book was released, and on the positive side the editor copied the homework format of the Chemistry and Physics author, so now it has three phases for homework. They also added statistics collected over the last ten to fifteen years (maybe more) to show how people do on the questions, so you can get a very good idea where you lie. On the downside, it looks like the error in paragraph two of this explanation is still there.