Scientists have taken an important step forward in understanding the human genome - our genetic blueprint - by fully deciphering the enigmatic Y chromosome present in males, an achievement that could help guide research on infertility in men. Researchers on Wednesday unveiled the first complete sequence of the human Y chromosome, which is one of the two sex chromosomes - the X chromosome being the other - and is typically passed down from male parent to male offspring. It is the last of the 24 chromosomes - threadlike structures that carry genetic information from cell to cell - in the human genome to be sequenced.