Israeli researchers have found the so-called “Ashkenazi mutation,” a genetic marker unique to European Jews, in a tribe of Indians in Colorado. They believe the gene was introduced into the tribe by a single Jewish male descended from Jews expelled from Spain in 1492.
A number of these Spanish Jews settled in the new world. As this 2008 article from Smithsonian points out, genetic markers have been found in the Spanish Catholic population of Colorado and New Mexico before, but never in a tribe of Native Americans.
The gene, BRCA1, is problematic because its mutation is linked to an aggressive form of breast cancer.
When normal and healthy, BRCA1 helps to protect breast and ovarian cells from cancer. An extremely long gene, it has thousands of DNA letters, each corresponding to one of four chemical compounds that make up the genetic code and run down either strand of the DNA double helix; a “misspelling”—a mutation—can occur at virtually any letter. Some are of no consequence, but the deletion of the chemicals adenine (A) and guanine (G) at a site 185 rungs into the DNA ladder—hence the name 185delAG—will prevent the gene from functioning. Then the cell becomes vulnerable to a malignancy. To be sure, most breast and ovarian cancers do not run in families. The cases owing to BRCA1 and a similar gene, BRCA2, make up less than 10 percent of cases overall.
By comparing DNA samples from Jews around the world, scientists have pieced together the origins of the 185delAG mutation. It is ancient. More than 2,000 years ago, among the Hebrew tribes of Palestine, someone’s DNA dropped the AG letters at the 185 site. The glitch spread and multiplied in succeeding generations, even as Jews migrated from Palestine to Europe. Ethnic groups tend to have their own distinctive genetic disorders, such as harmful variations of the BRCA1 gene, but because Jews throughout history have often married within their religion, the 185delAG mutation gained a strong foothold in that population. Today, roughly one in 100 Jews carries the harmful form of the gene variant.