All individuals carry a sex chromosome, the 23rd pair. Females carry XX and males carry XY. The Y chromosome is passed down as a direct paternal lineage from generation-to-generation by fathers to their son with very little mutation over time. Since the Y chromosome is so stable a strong comparison can be performed using other paternal male family members, such as a grandfather, alleged father’s brother or even another male sibling where the paternity relationship was known. The Y chromosome test is an alternative way to prove paternity when the alleged father is unavailable or deceased. All weekend appointments must have a 24 hour in advance verbal confirmation. Thanks!