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Evolution and Protein Folds

Stephen W. Schaeffer sws4 at PSUVM.PSU.EDU
Fri Jul 1 08:41:49 EST 1994

    I think that as Steve Karl said, DNA duplication occurs quite often in 
genomes.  Allozyme loci of Drosophila once thought to be encoded by single 
genes are part of small duplicate gene families, e.g, amylase, esterase, 
alcohol dehydrogenase.  These gene families are in various phases of 
diversification, amylase and esterase are examples of relatively recent 
duplications while alcohol dehydrogenase in the melanogaster group 
represents an ancient duplication.  I think that one benefit of 
early duplication events is to provide the organism with genetic 
redundancy.  Deleterious mutations in one gene is compensated by the 
second copy.
    Not all genes will duplicate in the genome though.  Consider the case 
of Down's syndrome patients who have an extra copy of chromosome 21.  We 
know that at least one gene on chromosome 21 causes these patients to 
be sterile when it is present in three copies.  Thus, I would predict that 
not all genes in the genome may be duplicated to generate proteins with new 
    An interesting question, are there any common genetic properties 
in genes that can or cannot be duplicated in the genome?  
Stephen W. Schaeffer
Institute of Molecular Evolutionary Genetics
The Pennsylvania State University

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