Biol10005 MST practice question help

[ChickenCh0wM1en]

Hi guys! Just wondering if someone could explain how to do this question??

Thanks!

[Hehetymen]

Is it C?

[vox nihili]

YES! how did you get it??!!

You have to knock out the first two because you never actually see P active, so there's no evidence for it being involved in that biochemical pathway.

In two, you've got MNO there. But in one it's only MO. So that suggests that the pathway is M->O->N

One: MO enzyme active, ON enzyme not functioning
Two: MO enzyme active, ON enzyme active
Three: MO enzyme not functioning, ON enzyme unknown whether it's working.


That's not a particularly good explanation, but hopefully that makes enough sense. If not, I'll give English a shot hahah

[Hehetymen]

YES! how did you get it??!!

All 3 strains grow on M but not P so M is last in the pathway and P is first. 2 grows on MNO but 1 only grows on MO so it must be P > N > O > M. This means options A and B are wrong. Option D is wrong because M is last in the pathway. C is right because strain 1 can grow on O (so it can convert O to M) and M but it can't grow on N (can't convert N to O).

[hobbitle]

*facepalm* I'm having a lot of trouble with Dawn's content over lectures 6-12 or so.  Hadn't done any biology before last semester so it's all pretty new (and confusing).  That question stumped me too.

[Hehetymen]

Hey man! How did you get to the fact that P is first and M is the last in the pathway??

All of them grow on M so M is the final product. Say the PNOM pathway aims to make glucose for the cell to use and M is glucose. If you give them glucose directly, then you don't need PNO. All three strains can grow on M so M must be the final product. More specifically, strain 3 confirms this as strain 3 can only grow on M. P is first in the pathway because none of them can grow on P but strain 1 can grow on MO and strain 2 can grow on MNO. I.e. N and O must be later in the pathway. If N or O were earlier in the pathway then it wouldn't make sense. Something like N > O > P > M wouldn't make sense because if we give strain 1 P directly it can't grow yet if we give it O it can grow. O cannot be earlier in the pathway than P. Same thing for strain 2.

[vox nihili]

Hey I somewhat see where you are coming from hahaha! When you say ON enzyme working that means compound O to N right?
But choice C says enzyme converting N to O?

I think the other explanations may be better. I haven't actually done this subject and misinterpreted the question

[pink0829]

I don't think the right answer is in the choices given. None of the choices seem to fit my pathway:

S-> A-> T-> B-> R

Maybe check with Dawn. I remember having this question in our practice problems last year.

Edit: I've checked my folder and the question wasn't a multiple choice question. We had to work out the pathway and identify where each mutant was blocked. It's the exact same information though and none of my answers match the choices. There might be a mistake in the question.

[Hehetymen]

Legend! Thanks so much!

I followed your logic with another problem and I cant seem to get the right answer... Do you mind checking this one for me?

All of them can grow on R so R is last. None can grow on S so S is first. 3 cannot grow on S and A so A is after S. 1 cannot grow on ATS so T is after A. So far we have S > A > T. Strains 1, 2, and 3 can all grow on B. Strain 4 can grow on R but cannot grow on B. B would have to be before R and after T (strain 1 can grow on B but not T).

S > A > T > B > R.

None of the answers seem to be correct though. A is wrong, C is wrong. B and D could both be correct IMO.

[pink0829]

I'll give you a couple of hints to get you started with the crosses and the genotypes. If you still have trouble working it out I can post my answer up.

• You would have recognised these were reciprocal crosses. So you have to determine if the trait is sex-linked.
• For moths, butterflies, fish and birds the ZW notation is used instead of XY. For these animals, males are homozygous (ZZ) and females are heterozygous (ZW).

• In sex-linked crosses, if the male offspring of the two crosses have different phenotypes and the female offspring have the same phenotype, the trait is X-linked. If the female offspring have different phenotype and male offspring are of the same phenotype then ZZ or ZZ notation is used- a tip if you weren't sure if you should use XY or ZW
• Start off by drawing out the crosses:
  Cross 1:
  
  F silver     x      M gold
  (Imagine an arrow pointing down)
  F gold               M silver
  Cross 2:
  
  F gold    x    M silver
  (Imagine an arrow pointing down)
  F silver        M silver
         
  Now fill in the Genotypes underneath each phenotype and work out what colour is dominant. Hint: look at the heterozygous offspring in cross 2.
  

It's really good that you are doing all these questions. It definitely would pay off

[hobbitle]

I'll give you a couple of hints to get you started with the crosses and the genotypes. If you still have trouble working it out I can post my answer up.

• You would have recognised these were reciprocal crosses. So you have to determine if the trait is sex-linked.
• For moths, butterflies, fish and birds the ZW notation is used instead of XY. For these animals, males are homozygous (ZZ) and females are heterozygous (ZW).

• In sex-linked crosses, if the male offspring of the two crosses have different phenotypes and the female offspring have the same phenotype, the trait is X-linked. If the female offspring have different phenotype and male offspring are of the same phenotype then ZZ or ZZ notation is used- a tip if you weren't sure if you should use XY or ZW
• Start off by drawing out the crosses:
  Cross 1:
  
  F silver     x      M gold
  (Imagine an arrow pointing down)
  F gold               M silver
  Cross 2:
  
  F gold    x    M silver
  (Imagine an arrow pointing down)
  F silver        M silver
         
  Now fill in the Genotypes underneath each phenotype and work out what colour is dominant. Hint: look at the heterozygous offspring in cross 2.
  

It's really good that you are doing all these questions. It definitely would pay off

I was struggling over this question too but I had forgotten that moths had the different gametic composition, thanks for reminding me... makes sense now.

[pink0829]

turns out I just got the chromosome system wrong! I just got the answer! :PP thanks so much again!!!!!! :DDD

I was struggling over this question too but I had forgotten that moths had the different gametic composition, thanks for reminding me... makes sense now.

No worries guys! Good luck with the midsem

[LeviLamp]

Just realised the MST is supposed to test us on our knowledge of Pracs 1 and 2. Do the Biology staff actually put questions relating to the pracs on the Genetics MST? D:

[vox nihili]

Just realised the MST is supposed to test us on our knowledge of Pracs 1 and 2. Do the Biology staff actually put questions relating to the pracs on the Genetics MST? D:

We copped one on ours in Biomed.

[hobbitle]

Just realised the MST is supposed to test us on our knowledge of Pracs 1 and 2. Do the Biology staff actually put questions relating to the pracs on the Genetics MST? D:

Sure there might be one or two.  Did you do the pracs?