Final answer:
Prenatal genetic diagnosis (PGD) can detect genetic conditions like sickle cell anemia and Down's syndrome in embryos, but cannot diagnose the inheritance of sexually transmitted diseases. Such diseases are not genetic and are not detected through embryo DNA screening.
Step-by-step explanation:
The question posed pertains to prenatal genetic diagnosis (PGD), which is a highly specialized procedure used to identify genetic disorders in embryos before they are implanted in the mother's uterus during in vitro fertilization. Specifically, the query is about what PGD cannot diagnose. Among the listed options, PGD can detect the inheritance of sickle cell anemia, Down's syndrome, and determination of sex.
However, PGD cannot diagnose the inheritance of sexually transmitted diseases as these are not genetic conditions that are passed down through the embryo's DNA, but rather infections that can be transmitted through other means. Treating and diagnosing genetic disorders often involves methods like amniocentesis for prenatal testing, and genetic counseling can aid prospective parents in understanding the risks of genetic abnormalities.