Family history (FH or FHx) consists of information about disorders from which the direct blood relatives of the patient have suffered. Genealogy typically includes very little of the medical history of the family, but the medical history could be considered a specific subset of the total history of a family.[citation needed] Accurate knowledge of a patient's family history may identify a predisposition to developing certain illnesses, which can inform clinical decisions and allow effective management or even prevention of conditions. Other medical conditions are carried only by the male line, though these Y-linked conditions are rare owing to the small size of the Y Chromosome. Tracing male ancestors may be impossible if the conception is due to rape or sexual activity outside of a marriage.