Putative gene is a predicted sequence, mean the functional expression are not yet shown in experimental studies, is a segment of DNA whose protein, and its function, is not known, but based on its open reading frame, it is believed to be a gene. 'Putative' means 'supposed to exist' - so a putative gene is a gene that you think exists but have no direct evidence for. For example, you may have identified a phenotype that appears to depend on a single gene - but the gene has not yet been identified.
I hope this concept of putative gene serve you to understand.