Karyotype (IMAGE) Whitehead Institute for Biomedical Research Caption In the rare human cell line used for this genetic screen, the cells have only one copy of each chromosome, except for chromosome 8, which has two copies. Because this cell line has only one copy of almost all of the chromosomes, it is ideal for efficiently making knockout human cells. Credit <i>Science</i>/AAAS 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.