ETCHbox genes are eutherian-specific homeobox genes expressed during preimplantation development at a time when the first cell lineage decisions are being made. The mouse has an unusual repertoire of ETCHbox genes with several gene families lost in evolution and the remaining two， and ， greatly divergent in sequence and number. Each has undergone duplication to give a double homeodomain locus and a large cluster of over 60 loci. The gene content differences between species raise important questions about how evolution can tolerate loss of genes implicated in key developmental events.
ETCHbox genes are eutherian-specific homeobox genes expressed during preimplantation development at a time when the first cell lineage decisions are being made. The mouse has an unusual repertoire of ETCHbox genes with several gene families lost in evolution and the remaining two， and ， greatly divergent in sequence and number. Each has undergone duplication to give a double homeodomain locus and a large cluster of over 60 loci. The gene content differences between species raise important questions about how evolution can tolerate loss of genes implicated in key developmental events.
