Human and herring X and Y chromosomes (IMAGE) Uppsala University Caption A comparison of human and herring X and Y chromosomes. The old human chromosome Y is small and contains few genes. The young herring chromosome Y retains all genes present on chromosome X and has an additional three genes in the sex-determining region. Credit Nima Rafati. Usage Restrictions May only be published in connection to reports about the research by Rafati et al. or after permission from Nima Rafati. 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.