The figure shows the genetic makeup of a germ line cell and a mature B

The figure shows the genetic makeup of a germ line cell and a mature B

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1. The figure shows the genetic makeup of a germ line cell and a mature B-cell at the loci controlling heavy chain production. Germ line DNA has many (up to 200) different variable (V) region genes, in addition to 12 diversity (D) region genes and four joining (J) region genes. During differentiation of this cell into the B-cell, rearrangement of the DNA occurs. This rearrangement aligns one of the many V genes with one of the D genes and one of the J genes, producing a functional VDJ recombinant gene. Since any of the genes may recombine with any others, this
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Unformatted text preview: rearrangement has the potential to generate 200 x 12 x 4 = 9600 different possible combinations. The same type of event occurs in the genes encoding the immmunoglobulin light chains where about 200 different V regions may recombine with about 5 different J regions giving rise to 200 x 5 = 1000 possible light chains. Since in any particular B-cell, any light chain combination can occur along with any heavy chain combination, the total possible immunoglobulin combinations approaches 10 7 (9600 x 1000)....
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