Approximately 10 percent of infants are born with a congenital heart defect, with one of the most common being persistent truncus arteriosus—a hole in the heart. New research conducted in the Caltech laboratory of Marianne Bronner, Albert Billings Ruddock Professor of Biology and director of the Beckman Institute uses chicken embryos as a model organism, to discover the genetic pathways that certain stem cells utilize to properly form heart tissues. The research appeared in a paper in the journal Developmental Cell on May 4.