X Marks the Spot (IMAGE) Brown University Caption X chromosomes are easy to spot in these bundles of DNA because the reddish 'male-specific lethal' protein has been made to fluoresce along their length. Credit Leila Rieder Usage Restrictions with credit 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.