In the zebra finch, an extra chromosome exists in the reproductive, or germline, cells. (Songbirds have 40 chromosomes and 41 with the extra chromosome.) Known as the germline-restricted chromosome, its sequence is largely unknown and none of its genes have been identified, until now. Using sophisticated genome-sequencing techniques, American University researchers have identified the first gene of the GRC. This finding could pave the way for further research into what makes a bird male or female.