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Otago HSFY chat - archive

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Haha fun times, just wait until final exams!
 
There was a diagram of two chromosomes of equal size joined together at several points. One question asked when such a structure would be seen (heaps of people put metaphase I - wrong), another asked in what tissue such a structure would be seen if it involved the human X chromosome (you won't get full marks here for writing "gonads" - consider why), another question asked the name of the structure and how many you would find per cell in a human male (this is where it gets a bit contentious - do you put 22 or 23? I'm still not 100% sure on this one).
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When you say "two chromosomes of equal size", do you mean the "I" form or the "X" form? (Both can be referred to chromosomes).
- If it's two "I" chromomes (so one "X" structure since they're joined) it would be seen (possibly) in prometaphase and metaphase.
- If you're referring to two "X" structures together (so it looks like "XX") then that would be in prophase 1, and metaphase 1 of meiosis.

It sounds like they're crossing over since you said "joined together at several points"; so I'm guessing you're leaning towards prophase 1 of meiosis with your answer.

Why would you not get full marks for gonads? (Assuming it's meiosis - I must be missing something here :blink:)

do you put 22 or 23?
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Why would you put 22...what's your argument for that?
 
I think the 22 or 23 debate revolves around the fact they are two chromosomes of equal size. I'm sure you understand that there are 22 autosomal chromosome pairs, and 1 pair of sex chromosomes - which in a human male would not appear equal in size!

If it involved the X chromosome it could also be found on the ovaries, perhaps? (well it should be! X-chromosomes replicate via meiosis there too!)
 
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Podolski said:
- If it's two "I" chromomes (so one "X" structure since they're joined) it would be seen (possibly) in prometaphase and metaphase.
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No, this would be two chromatids joined together - but while they are joined the overall structure is one chromosome.

Podolski said:
It sounds like they're crossing over since you said "joined together at several points"
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The diagram is on page 13 of the 2007 CELS191 final exam.

Podolski said:
Why would you not get full marks for gonads? (Assuming it's meiosis - I must be missing something here :blink:)

Why would you put 22...what's your argument for that?
Click to expand...

Maybe one of the HSFYers can answer that - no point sharing questions with them if they don't actively participate in thinking about and working out the answers.

EDIT - and ChickenPie has already provided his thoughts
 
No wonder I was confused about it in exam, Im still confused about it now

I think you on the right track chickenpie, but not quite
 
No a chromatid is one half of a chromosome when both "I" are together to form the "X".
When it's on it's own as in the "I" it should be referred to as a chromosome as well. But it is not because it is taught wrong in most textbooks etc.

The term "gonads" also refers to ovaries. It's just slang that people assume it's "testes only".

And yea it's 22 if the question asked "are there 22 or 23 equal sized chromosomes"...that's pretty obvious. But it's not clear from your post if that was still part of the question or if they're merely asking how many pairs of chromosomes exist.

Lol I really can't be bothered digging up the exam to look at it...
 
Hmm yeah it would be so much easier with the exam question in front of me, cos I dont actually know what the question is asking.
But I cant be bothered looking up the exam either haha:lols:
 
SASOL said:
Hmm yeah it would be so much easier with the exam question in front of me, cos I dont actually know what the question is asking.
But I cant be bothered looking up the exam either haha:lols:
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I lost track ages back. I hope everyone isn't freaking out about this question. I would put my two cents in but I think most of the views has been covered.

Don't freak out.
 
Podolski said:
No a chromatid is one half of a chromosome when both "I" are together to form the "X".
When it's on it's own as in the "I" it should be referred to as a chromosome as well. But it is not because it is taught wrong in most textbooks etc.
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Correct - when a chromatid is on its own it is a chromosome, but when it is one half of a duplicated chromosome then it is a chromatid - and the whole 2 chromatid structure is referred to as one chromosome. In your previous post you suggested that such a structure could be referred to as two chromosomes - that's all I was getting at.

Podolski said:
The term "gonads" also refers to ovaries. It's just slang that people assume it's "testes only".
Click to expand...

It is precisely because gonads means both testes and ovaries that putting "gonads" as the answer would not get you full marks.

Podolski said:
And yea it's 22 if the question asked "are there 22 or 23 equal sized chromosomes"...that's pretty obvious. But it's not clear from your post if that was still part of the question or if they're merely asking how many pairs of chromosomes exist.
Click to expand...

I think that was where much of the debate emerged - it wasn't completely clear what the question was meaning in this sense. Either way, lots of people still completely forgot to consider that the X and Y chromosomes are different when answering that question = lost marks.
 
The entire tetrad/chromatid/homologue/chromosome terminology is indeed difficult to get your head around...

I get the gonad question now... bleh. Need to learn meiosis in greater depth! That's a common misconception I was a part of, i want to kick myself in the nuts (not gonads!) for that.
 
It is precisely because gonads means both testes and ovaries that putting "gonads" as the answer would not get you full marks.
Click to expand...

Right so you're saying that since they're "equal size" this particular type of crossing over ONLY occurs in females (as they have two X's) and the male X-Y crossover would have two chromosomes unequal in size?
This of course is all only true if the question actually meant meiosis and that they were asking about chromosomes of "equal length"...

I hate questions like this...it's pretty ambiguous a lot of the time. It's also been like 3 years since I did any basic genetics :blink:
 
Podolski said:
Right so you're saying that since they're "equal size" this particular type of crossing over ONLY occurs in females (as they have two X's) and the male X-Y crossover would have two chromosomes unequal in size?
This of course is all only true if the question actually meant meiosis and that they were asking about chromosomes of "equal length"...

I hate questions like this...it's pretty ambiguous a lot of the time. It's also been like 3 years since I did any basic genetics :blink:
Click to expand...

There is X-Y crossover????
 
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