Genesis of the <i>Xenopus</i> Ancestor (IMAGE) Hokkaido University Caption Two ancestral species with nine pairs of chromosomes, S and L, mate to produce a hybrid S/L offspring with 18 chromosomes that do not pair. This sterile offspring undergoes whole genome duplication to produce a new fertile species with 18 pairs of chromosomes that is ancestral to all Xenopus species. For clarity, the process is rendered here with only one type of chromosome. Credit Copyright: 2016 Masanori Taira Usage Restrictions This image is copyrighted and can be used for reporting scientific works described in this press release with appropriate credit(s). 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.