Abstract
Comparative and phylogenetic analyses of homologous sequences from closely related species reveal genetic events which have happened in the past and thus provide considerable insight into molecular genetic processes. One such process which has been especially important in the evolution of multigene families is gene conversion. The fetal gamma 1 and gamma 2-globin genes of catarrhine primates (humans, apes, and Old World monkeys) underwent numerous gene conversion events after they arose from a gene duplication event 25-35 million years ago. By including the gamma 1- and gamma 2-globin gene sequences from the common gibbon, Hylobates lar, the present work expands the gamma-globin data set to represent all major groups of hominoid primates. A computer-assisted algorithm is introduced which reveals converted DNA segments and provides results very similar to those obtained by site-by-site evolutionary reconstruction. Both methods provide strong evidence for at least 14 different converted stretches in catarrhine primates as well as five conversions in ancestral lineages. Features of gene conversions generalized from this molecular history are 1) conversions are restricted to regions maintaining high degrees of sequence similarity, 2) one gene may dominate in converting another gene, 3) sequences involved in conversions may accumulate changes more rapidly than expected, and 4) certain elements, such as polypurine/polypyrimidine [Y)n) and (TG)n elements, appear to be hotspots for initiating or terminating conversion events.
Highlights
From the *Department of Anatomy the §Diuision of Molecular Biology, Mainones, Morris Goodman+, and Jerry L
The fetal y’ and -y2-globin genes of catarrhine primates underwent numerous gene conversion events after they arose from a gene duplication event 25-35 million years ago
By including the yl- and y2-globin gene sequences from the common gibbon, Hylobates lar, the present work expands the y-globin data set to represent all major groups of hominoid primates
Summary
Bethesda Research Laboratories or New England Biolabs and used as specified by the vendor. The plasmid subclones which contain the gibbon globin genes and intergenic regions are shown below the X clones, and they are designated according to the parent clone, restriction enzyme site used for subcloning, and fragment size. The computer-assisted analysis of gene conversions introduced in this work uses the parsimony program PAUP to evaluate a set of user-specified trees at small intervals along the sequence alignment. Batch files were set up as required for PAUP which were designed to evaluate the aligned y-globin sequences (Fig. 2) in windows 20-bp wide at intervals (“‘jumps”) of 10 bp. These parameters provide an overlap such that sites are always evaluated in the context of their nearest neighbors.
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