 But the Marranos (Crypto-Jews) and returned Sephardim represent the remainder.According to a 2008 study by the American Journal of Human Genetics, 19.8% of the Portuguese population has some degree of Jewish ancestry.The genetic signatures of people in the Iberian Peninsula provide new evidence that the number of Jews forced to convert to Christianity during Catholic rule in the 15th and 16th centuries was much greater than historians believed.