A sequence fragment of Deoxyribonucleic acid (DNA) in Drosophila was used in Basic Local Alignment Search Tool (BLAST search) and its best match was to a kinase gene from Neurospora. This means that the Drosophila sequence contains a kinase gene.
As the organisms have common ancestors, they also have genes with similar sequences in common. So, a gene will have relatives among the genes isolated and sequenced in other organisms especially in the closely related ones.
If the sequence of the candidate is closely resemble that of a gene previously identified from another organism. Then this resemblance provides a strong indication that the candidate gene is the real gene. Less close matches are also useful.