Single-Copy Inverted Repeats Associated with Regional Genetic Duplications in γ Fibrinogen and Immunoglobulin Genes

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Abstract
A portion (150 base pairs) of the 7th exon of the human .gamma. fibrinogen gene is duplicated in the preceding intron. This duplicated sequence, termed a pseudoexon is flanked on each side by a single-copy inverted repeat sequence consisting of 102 base pairs. Frequencies of point substitutions indicate that both the pseudoexon and the inverted repeat sequence arose .apprx. 10-20 million yr ago. The generality of this type of duplication is suggested by the occurrence of a similar duplication in the mouse Ig .mu.-.delta. region. As in the fibrinogen pseudoexon, the portion of the Ig .mu.-.delta. region containing the duplication and the inverted repeat was reported to be single-copy in the mouse genome. Since both of the first 2 single-copy inverted repeats to be sequenced are associated with regional duplications, many of the single-copy inverted repeat seuqences, which make up 1-2% of the genome, may also be associated with regional duplications.