Final answer:
Klinefelter syndrome (XXY) is the sex chromosome abnormality associated with an increased risk of breast cancer and infertility.
Step-by-step explanation:
Klinefelter syndrome (XXY) is the sex chromosome abnormality associated with an increased risk of breast cancer and infertility. Individuals with Klinefelter syndrome typically have small testes, enlarged breasts, and reduced body hair. The extra X chromosome undergoes inactivation, resulting in reduced fertility and an increased risk of breast cancer.