EVIDENCE OF GENETIC VARIATION IN THE HUMAN SEX RATIO

It has been suggested that the probability of conceiving a male rather than a female varies from family to family. If this variation were connected with variations in the Y chromosome, then all males belonging to a family with a preponderance of males should have an excess of male children. In females no such relation could hold. The truth of this was tested on a sample of 1592 male and 697 female medical and dental students in Athens, whose family trees were known. There is indeed a statistically significant tendency for students to belong to sibships with a higher percentage of males when their father's subship also had a preponderance of males. Students whose father's sibship had a preponderance of females belonged to a sibship with a lower percentage of males. No similar relation was found when students sibships were classified by preponderance of males or females in their mother's sibship.