In his new book, “Legacy: A Genetic History of the Jewish People,” Harry Ostrer, a medical geneticist and professor at Albert Einstein College of Medicine in New York, claims that Jews are different, and the differences are not just skin deep

Jews exhibit, he writes, a distinctive genetic signature which Ostrer sees as central to Jewish identity. Geneticists have long been aware that certain diseases, from breast cancer to Tay-Sachs, disproportionately affect Jews. Ostrer, who is also director of genetic and genomic testing at Montefiore Medical Center, goes further, maintaining that Jews are a homogeneous group with all the scientific trappings of a distinct race.