When fraternal twins are male and female, there is a chance the female will be sterile. This is a condition called freemartin in which the female was masculinized by its male twin’s hormones during embryonic development. Stem cells also flow from the male twin to the female twin. The female twin therefore contains many cells with a Y chromosome. Genetic testing to identify the Y chromosome in the female twin can determine if the female will be sterile.

Currently this test is in development. For more information regarding the Freemartin testing program contact Jim Simpson at This e-mail address is being protected from spambots. You need JavaScript enabled to view it. .