Gene Copies, Pairing up in Stem Cells (IMAGE) Cold Spring Harbor Laboratory Caption We and other mammals have two copies of each gene, and each copy, or 'allele,' was thought to remain physically apart from the other in the cell nucleus. David Spector's team now finds that the alleles of a specific gene, Oct4, can and do pair up in mammalian cells. (Oct4 gene alleles are labeled in green; other DNA is stained blue; cell nuclei are outlined in red). The Oct4 alleles were observed to pair up just as embryonic stem cells differentiated into specific cell types. Credit Spector Lab, CSHL Usage Restrictions must give 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.