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  #1  
Old 08-30-2012
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Question Results of this mutation?

A family in which several individuals have arthritis and detached retina is diagnosed with Stickler Syndrome.The locus for Stickler Syndrome has been mapped near that for Type 2 collagen on chromosome no-12 and mutations in the COL2A1 gene have been described in Stickler Syndrome.The family became interested in molecular diagnosis to distinguish normally from mildly affected individuals.Which of the results would be expected in an individual with an individual with a promoter mutation at one COL2A1 gene locus?

a.)Western Blotting detects no type2 collagen chains.
b.)Southern blotting using intronic restriction sites yields normal restriction fragment sizes.
c.)Reverse transcriptase-polymerase chain reaction(RT-PCR) detects one half normal amounts of COL2A1 mRNA in affected individuals.
d.)Fluorescent in situ hybridization (FISH) analysis using a COL2A1 probe detects signals on only one chromosome 12
e.)DNA sequencing reveals a single nucleotide difference between homologus COL2A1 exons.
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I would go with B
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i guess it's C) RT-PCR detects one half normal amounts of COL2A1 mRNA in affected individuals.

coz..the individual has the mutation in promoter of one COL2A1...so, trancription do not take place....so, only half amount of genes are seen in RNA.....
i guess i'm wrong though...
nice question......please post the answer...
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d


pls give ans..

thx
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d.)Fluorescent in situ hybridization (FISH) analysis using a COL2A1 probe detects signals on only one chromosome 12
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Default my answer

c.)Reverse transcriptase-polymerase chain reaction(RT-PCR) detects one half normal amounts of COL2A1 mRNA in affected individuals.
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The correct answer is (c)

Here's the explanation :-

After the locus responsible for a genetic disease is mapped to a particular chromosome region,"candidate" genes can be examined for molecular abnormalities in affected individuals.The connective tissue abnormalities in Stickler syndrome makes the COL2A1 collagen locus an attractive candidate for disease mutations,prompting analysis of COL2A1 gene structure and expression.
1.)Western blotting detects gene alterations that interface with protein expression.
2.)RT-PCR detects alterations in mRNA levels,Each analysis should detect one half the respective amounts of COL2A1 protein or mRNA in the case of a promoter mutation that abolishes transcription of one COL2A1 allele.
3.)Southern blotting detects nucleotide changes that alter DNA restriction sites but it is relatively insenstive unless large portions of the genes are deleted.
4.)FISH analysis using DNA probes from the COL2A1 locus is a senstive methos for detecting deletions of the entire locus
5.)DNA sequencing of the entire gene provides the gold standard for detecting any alteration in the regulatory or coding sequences.
Nucleotide sequence changes are still subjected to interpretation since they may represent polymorphisms that do not alter gene function.Population studies or in vitro studies of gene expression are often needed to discriminate DNA polymorphisms from mutations that disrupt gene function.For any autosomal locus the interpretation of molecular analysis is complicated by the presence of two homologus copies of the gene.
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Hi Skyprincess

Thanks for the Q and the Ans...

It would be helpful if could also site the source of the question
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Old 08-31-2012
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Quote:
Originally Posted by Skyprincess View Post
The correct answer is (c)

Here's the explanation :-

After the locus responsible for a genetic disease is mapped to a particular chromosome region,"candidate" genes can be examined for molecular abnormalities in affected individuals.The connective tissue abnormalities in Stickler syndrome makes the COL2A1 collagen locus an attractive candidate for disease mutations,prompting analysis of COL2A1 gene structure and expression.
1.)Western blotting detects gene alterations that interface with protein expression.
2.)RT-PCR detects alterations in mRNA levels,Each analysis should detect one half the respective amounts of COL2A1 protein or mRNA in the case of a promoter mutation that abolishes transcription of one COL2A1 allele.
3.)Southern blotting detects nucleotide changes that alter DNA restriction sites but it is relatively insenstive unless large portions of the genes are deleted.
4.)FISH analysis using DNA probes from the COL2A1 locus is a senstive methos for detecting deletions of the entire locus
5.)DNA sequencing of the entire gene provides the gold standard for detecting any alteration in the regulatory or coding sequences.
Nucleotide sequence changes are still subjected to interpretation since they may represent polymorphisms that do not alter gene function.Population studies or in vitro studies of gene expression are often needed to discriminate DNA polymorphisms from mutations that disrupt gene function.For any autosomal locus the interpretation of molecular analysis is complicated by the presence of two homologus copies of the gene.
hey! cn u xplain y A cant b d answer? if dre is a promoter mutatn n d gene is not trascribd d protein wont b expressd rit?? so western blot will nt b abl to detct dat protein rit??
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Quote:
Originally Posted by viral View Post
Hi Skyprincess

Thanks for the Q and the Ans...

It would be helpful if could also site the source of the question
Hey hi!

I have some photostat test papers in random order for self assessment,i got them from a senior of mine.Its prolly from some book,its just written on the top of every page "clinical vignettes for the USMLE step 1" so its hard to tell which book is it from.In case I come to know i'll surely let you know.
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Quote:
Originally Posted by sruthi View Post
hey! cn u xplain y A cant b d answer? if dre is a promoter mutatn n d gene is not trascribd d protein wont b expressd rit?? so western blot will nt b abl to detct dat protein rit??
Hey sruthi,sorry i do not know the explanation for that.Infact I dint even know the answer to this question exactly,I had to search for ages for the answers page of this question!Its a very confusing question acc to me and your question is apt,it'll be great if somebody answers this!
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Quote:
Originally Posted by sruthi View Post
hey! cn u xplain y A cant b d answer? if dre is a promoter mutatn n d gene is not trascribd d protein wont b expressd rit?? so western blot will nt b abl to detct dat protein rit??
i'm not sure is it true....but, i'm posting wat i thought about this one and eliminated this....

yes, promoter mutation lead to gene not being expressed...i guess in western blot we are able to find the collagen 2 chains....but we find a mutation at chr.12 site...
i'm not sure abt it....but i thought it like this...correct me if u know,...
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Quote:
Originally Posted by venky2600 View Post
i'm not sure is it true....but, i'm posting wat i thought about this one and eliminated this....

yes, promoter mutation lead to gene not being expressed...i guess in western blot we are able to find the collagen 2 chains....but we find a mutation at chr.12 site...
i'm not sure abt it....but i thought it like this...correct me if u know,...
i mean.......in western blot we can find both collagen 2 chains.....but we can see the mutated gene at chr.12 of the chain....
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