Question about genetic diversity Watch

abbeyjayne
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Hi! I've been practicing past paper questions for my AQA AS Biology exam on Thursday and usually my textbook gives references or directs you the paper that said question was found on.

However, I can't find the question below at all on any paper so if someone knows which paper it is from so I can use the mark scheme or is able to provide an 'unofficial' mark scheme for me, I'd be ever grateful. Thank you! Good luck to anybody else sitting this exam or the retakes later this week!

The question is as follows:

"Organisms vary widely in the number of genes they have. Figure 2 shows the total length of DNA in six organisms plotted against the number of functional genes. The length of DNA is measured in numbers of base pairs.

(i) A double-stranded DNA molecule is 2um long for every thousand base pairs. Use Figure 2 to calculate the total length of DNA in a human cell in metres. Show your working.

(ii) Calculate the ratio of DNA length to number of genes in humans and in Escherichia coli and suggest why there is this difference."

I found the figure (everything is the same except the scale of the x-axis) for this question here (but the question is entirely different). NOTE: The file automatically downloads!: https://www.google.co.uk/url?sa=t&rc...CbKnlpXELnP_OA

Any help would be much appreciated!
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Asklepios
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(Original post by abbeyjayne)
Hi! I've been practicing past paper questions for my AQA AS Biology exam on Thursday and usually my textbook gives references or directs you the paper that said question was found on.

However, I can't find the question below at all on any paper so if someone knows which paper it is from so I can use the mark scheme or is able to provide an 'unofficial' mark scheme for me, I'd be ever grateful. Thank you! Good luck to anybody else sitting this exam or the retakes later this week!

The question is as follows:

"Organisms vary widely in the number of genes they have. Figure 2 shows the total length of DNA in six organisms plotted against the number of functional genes. The length of DNA is measured in numbers of base pairs.

(i) A double-stranded DNA molecule is 2um long for every thousand base pairs. Use Figure 2 to calculate the total length of DNA in a human cell in metres. Show your working.

(ii) Calculate the ratio of DNA length to number of genes in humans and in Escherichia coli and suggest why there is this difference."

I found the figure (everything is the same except the scale of the x-axis) for this question here (but the question is entirely different). NOTE: The file automatically downloads!: https://www.google.co.uk/url?sa=t&rc...CbKnlpXELnP_OA

Any help would be much appreciated!

I can't find the figure, but the human genome is roughly 3 billion bp = 3 million kb. now if it is 2 μm for every kb, then total length = 6 million μm = 6 m.

For your second question, I don't have the data but divide DNA length (in bp) by number of genes. This number should be higher for humans as they are eukaryotic and have introns.
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abbeyjayne
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(Original post by Asklepios)
I can't find the figure, but the human genome is roughly 3 billion bp = 3 million kb. now if it is 2 μm for every kb, then total length = 6 million μm = 6 m.

For your second question, I don't have the data but divide DNA length (in bp) by number of genes. This number should be higher for humans as they are eukaryotic and have introns.
Ah. Based on the figure I have in my textbook, this is the calculations I did for part (a):
9,000 base pairs in human DNA. 2um x 10,000 = 20,000 per 1,000 base pairs. 20,000 x 9 = 180,000m.

And for part (b), this is what I put:
The ratio is 1:7. There is a difference between the two organisms because bacteria like E-coli are of much smaller size/have much smaller surface areas than humans so, therefore, have fewer cells and, thus, have less genes within their nuclei.

So I'm guessing those are probably wrong?

Thank you for your help by the way!
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abbeyjayne
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(Original post by Eggandegg)
I just came across the exact same problem. I don't know what aqa's game is but trying to teach yourself this specification with only the Sams paper and the garbage questions these textbooks come up with as practice is a ****ing nightmare. I have no idea where the answer to this question might be...
Where did you get 9000 Base pairs from though? I got 1000000000 i.e 10 to the power 9...
No idea tbh, this thread was posted quite a while ago now and I've actually dropped the subject (I'm in Year 13 now)! Sorry
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