DEFB126 Deleted Sperm (IMAGE) University of California - Davis Caption These are sperm from a donor with a defective gene for the coating protein. These sperm look normal and can swim, but have difficulty penetrating mucus. Credit Ted Tollner, UC Davis Usage Restrictions May be used with acknowledgement of the source. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.