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#1
01-12-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,590 Times in 660 Posts Reputation: 1600
How many idiotype possibilities!

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
F) 4000

#2
01-12-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 642 Times in 407 Posts Reputation: 652

D?
ugh i hate immuno so much, totally forgot how to do this stuff "-_-
#3
01-12-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 790 Threads: 76 Thanked 672 Times in 316 Posts Reputation: 690

I guess D........ i dont remem immuno much.....ahhhhh
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Matched!!!
#4
01-13-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,590 Times in 660 Posts Reputation: 1600

The correct answer is D) 1000

The light chain uses VJ combination .. so you would multiply V x J which gives you (200 x 5) = 1000

And that's it .. For idiotypes you don't need to take isotypes in consideration!
 The above post was thanked by: drortho (01-15-2012), Hitman (01-13-2012), step_enhancer (01-14-2012)

 Tags Genetics-, Immunology-, Step-1-Questions

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