DNA is packaged into threadlike structures called chromosomes. Most people have 46 chromosomes, or 23 pairs. One chromosome in each pair is inherited from a person’s mother and the other from the father. The 23rd pair of chromosomes are the sex chromosomes. These chromosomes determine whether a person is male or female. Typically, a male has one X and one Y chromosome, and a female has two X chromosomes. When a male child is conceived he receives the Y chromosome from his father and an X chromosome from his mother. When a female child is conceived, she receives an X chromosome from her father and an X chromosome from her mother.