Final answer:
An individual with an XXXY sex chromosome complement is best described as having Klinefelter syndrome. Klinefelter syndrome is a genetic disorder in males that results from having an extra X chromosome, resulting in physical and developmental characteristics such as small testes, enlarged breasts, reduced body hair, and reduced fertility.
Step-by-step explanation:
An individual with an XXXY sex chromosome complement is best described as having Klinefelter syndrome. Klinefelter syndrome is a genetic disorder in males that results from having an extra X chromosome, resulting in a genotype of XXY. Males with Klinefelter syndrome typically have physical and developmental characteristics such as small testes, enlarged breasts, reduced body hair, and reduced fertility.