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  #1  
Old 03-26-2014
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Default Immunology question!

A germline B lymphocyte possesses 200 distinct V region genes, 5 J region genes, and 2 isotypic possibilities to rearrange for its selection of light chain synthesis. Assuming no recombinational inaccuracies, how many distinct idiotypes could be produced by combining this coding sequence with one heavy chain?

A) 10
B) 205
C) 400
D) 1000
E) 2000
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  #2  
Old 03-26-2014
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I would go with D
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Old 03-26-2014
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You're right. But why not E? I mean there are two types of light chains; lambda and kappa. The book says that a heavy chain can bind to any two types of light chains and further contribute to diversity of the receptors. So since there are two types of light chains, does it not make sense that in this case there are 2000 possibilities? I mean I got the answer wrong so I am definitely not getting something right.
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Old 03-26-2014
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Correct Answer

Quote:
Originally Posted by eizou View Post
A germline B lymphocyte possesses 200 distinct V region genes, 5 J region genes, and 2 isotypic possibilities to rearrange for its selection of light chain synthesis. Assuming no recombinational inaccuracies, how many distinct idiotypes could be produced by combining this coding sequence with one heavy chain?

A) 10
B) 205
C) 400
D) 1000
E) 2000
i think they are "tricking you" with the "2 ISOTYPIC possibilities" wording of the light chains, they are asking you specifically of the idiotype, so this factor should not be taking into account (even though we know that both light and heavy chains take part in the idiotype, but here they mention ISOTYPE) and also they are asking idiotypes of ONE HEAVY CHAIN, so there you go,
only heavy chain data: 500 x 2 = 1000
let me know if im wrong
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Old 03-26-2014
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Quote:
Originally Posted by drpisho View Post
i think they are "tricking you" with the "2 ISOTYPIC possibilities" wording of the light chains, they are asking you specifically of the idiotype, so this factor should not be taking into account (even though we know that both light and heavy chains take part in the idiotype, but here they mention ISOTYPE) and also they are asking idiotypes of ONE HEAVY CHAIN, so there you go,
only heavy chain data: 500 x 2 = 1000
let me know if im wrong
Yea the isotypes don't play any role in the formation of the idiotypes. That's what the answer explanation says.
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