Sentence:  Polyclonal antibodies were prepared against the <WSD>"period</WSD>" gene product, which influences biological rhythms in D. melanogaster, by using small synthetic peptides from the per sequence as immunogens.<!--! No instance of "period" in the following quote !--> 
Meaning of the word marked with <WSD> tags:  A "Drosophila" gene, the gene product of which is involved in regulation of the circadian rhythm.