melanin101
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I'm redoing unit 1 bio for edexcel and these questions stump me. What does this question mean by genetic diagram?

http://qualifications.pearson.com/co...e_20120514.pdf

I'm stuck on this 5 marker, question 8 part c (or the second last question in the exam).

I know the answer to the question (0.25) but I don't know what it means by "drawing a genetic diagram". Does it want to me to draw a punett square? The mark scheme is very bare-bones:

(Original post by Mark scheme)
1. genotype of parents shown ;
2. alleles in the gametes shown ;
3. possible genotypes of children shown ;
4. corresponding phenotypes shown ;
5. (probability =) ¼ / 25% / 1 in 4 / 0.25 ;
helppppp!!!

thanks
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Asklepios
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(Original post by melanin101)
x
Yeah it wants you to draw a punett square or something similar
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Maria247
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Hope this helps
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melanin101
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(Original post by Asklepios)
Yeah it wants you to draw a punett square or something similar
Yeah, I thought so. Thanks!


(Original post by Maria247)
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Hope this helps
Exactly what I wanted, thank you so much!!!!!!
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Can someone help me with this though? A detailed answer would be appreciated.
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melanin101
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Can someone help me with this though? A detailed answer would be appreciated.
You need to combine what you know about scientific investigations and gene therapy.

So I'd answer it like this:
- Firstly the unaffected gene would be isolated, then it would be removed from the DNA (using special enzymes called restriction endonucleases). Then (using the enzyme ligase) the gene will be integrated into a liposome (or sometimes stem cells or even viruses). After this, the liposome with the gene would be injected into the dysfunctional (brain?) cells in the sheep.
- As it's an investigation, the symptoms and progress of the disease on the sheep would be monitored to see if the gene therapy has had an effect. The study would be repeated on many sheep (to keep the test reliable) and some sheep would be in a control group to make sure the test is valid.
-It's also worth noting that t currently gene therapy only provides a temporary fix (as treated cells are replaced and the introduced genes are subsequently lost) and so the treatment may need to be done again on the sheep.

EDIT: just checked the mark scheme and there are other things you could have mentioned such as: details on the control group's injection, the recording of the sheep's lifespan, info on comparing control group sheep to the study group.

EDIT 2: You don't really need to know the names of the enzymes (in italics) used to cut out and stick in the genes. I thought it would be nice to know so I included them anyway.

If anything else needs any extra explaining, I'll try to get back to you ASAP. Best of luck!!!!
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Asklepios
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(Original post by melanin101)
So I'd answer it like this:
- Firstly the unaffected gene would be isolated, then it would be removed from the DNA (using special enzymes called restriction endonucleases)
I don't think you'd use the original DNA sequence of the human gene. But ideally you'd want judt coding DNA (cDNA) that doesn't have introns and other non-coding regions. This is because something could probably go wrong with splicing if the gene isn't in its normal position in the chromosome.

You can do this by using the enzyme reverse transcriptase to create a complementary DNA strand, which can then be used in PCR. Alternatively you can synthesise the DNA from scratch and stitch bits together using various methods (e.g. Gibson assembly).

Another essential step in the process would be to test if gene replacement can rescue the disease cellular phenotype in human cell culture, and possibly in sheep too. You can do this by giving the DNA to the mutant cells, or could create an inducible mutant. Basically you can put in a bit of DNA that stops gene expression but which can be deleted out by site-specific recombinase proteins (e.g. Cre, FLP). These can be made inducible by fusion with oestrogen receptor so that once you administer tamoxifen they are active. Therefore, you can create a system whereby before you give tamoxifen the gene is inactive, and after, the gene become active. So you can study the effects of rescue at different developmental time points.



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melanin101
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(Original post by Asklepios)
I don't think you'd use the original DNA sequence of the human gene. But ideally you'd want judt coding DNA (cDNA) that doesn't have introns and other non-coding regions. This is because something could probably go wrong with splicing if the gene isn't in its normal position in the chromosome.

You can do this by using the enzyme reverse transcriptase to create a complementary DNA strand, which can then be used in PCR. Alternatively you can synthesise the DNA from scratch and stitch bits together using various methods (e.g. Gibson assembly).

Another essential step in the process would be to test if gene replacement can rescue the disease cellular phenotype in human cell culture, and possibly in sheep too. You can do this by giving the DNA to the mutant cells, or could create an inducible mutant. Basically you can put in a bit of DNA that stops gene expression but which can be deleted out by site-specific recombinase proteins (e.g. Cre, FLP). These can be made inducible by fusion with oestrogen receptor so that once you administer tamoxifen they are active. Therefore, you can create a system whereby before you give tamoxifen the gene is inactive, and after, the gene become active. So you can study the effects of rescue at different developmental time points.



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Thanks for this, it was a super interesting read!! The AS Biology spec and mark scheme doesn't go into that much detail though, all we ever learn is that the normal gene is found and put into a vector (virus/liposome) and it is subsequently injected into the target cell.
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Maria247
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(Original post by melanin101)
You need to combine what you know about scientific investigations and gene therapy.

So I'd answer it like this:
- Firstly the unaffected gene would be isolated, then it would be removed from the DNA (using special enzymes called restriction endonucleases). Then (using the enzyme ligase) the gene will be integrated into a liposome (or sometimes stem cells or even viruses). After this, the liposome with the gene would be injected into the dysfunctional (brain?) cells in the sheep.
- As it's an investigation, the symptoms and progress of the disease on the sheep would be monitored to see if the gene therapy has had an effect. The study would be repeated on many sheep (to keep the test reliable) and some sheep would be in a control group to make sure the test is valid.
-It's also worth noting that t currently gene therapy only provides a temporary fix (as treated cells are replaced and the introduced genes are subsequently lost) and so the treatment may need to be done again on the sheep.

EDIT: just checked the mark scheme and there are other things you could have mentioned such as: details on the control group's injection, the recording of the sheep's lifespan, info on comparing control group sheep to the study group.

EDIT 2: You don't really need to know the names of the enzymes (in italics) used to cut out and stick in the genes. I thought it would be nice to know so I included them anyway.

If anything else needs any extra explaining, I'll try to get back to you ASAP. Best of luck!!!!
Thankyou so much! How are you preparing for the exam btw? Have you finished doing the past papers?
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