Complete open reading frame sequences for Type I GnRH receptors, aligned using MUSCLE [] . The Type I receptors identified in chimaeras and coelacanths (uppermost sequences) share high sequence similarity with those from mammals as well as identical intron-exon boundaries (arrowheads) and the lack of a cytoplasmic C-terminal domain. Amino acids that are highly conserved (>80% sequence identity) are indicated with the darkest shading; lighter shading indicates 60-80% identity; the lightest shading indicates 40-60% identity; and a white background indicates low conservation (<40% identity). Transmembrane domains were predicted using HMMTOP 2.0  and are indicated with dark lines surrounding the relevant portion of the sequences. Latin names of species and accession numbers for sequences are provided in Additional file 1: Table S1.