Nomenclature
The SMAD proteins are homologs of both the Drosophila protein, mothers against decapentaplegic (MAD) and the Caenorhabditis elegans protein SMA (from gene sma for small body size). The name is a portmanteau of the two. Mad mutations can be placed in an allelic series based on the relative severity of the maternal effect enhancement of weak dpp alleles, thus explaining the name Mothers against dpp.
During Drosophila research, it was found that a mutation in the gene, MAD, in the mother, repressed the gene decapentaplegic in the embryo.
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