Baby mice fathered by mice receiving a donation of spermatogonial stem cells from mice expressing green fluorescent protein. Only half the baby mice show the green color. This is because each spermatogonial stem cell has only one copy of the gene for green fluorescent protein. When the spermatogonial cell divides, only half the cells that result from it have the gene for green fluorescent protein.
The NICHD is part of the National Institutes of Health (NIH), the biomedical research arm of the federal government. NIH is an agency of the U.S. Department of Health and Human Services. The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. NICHD publications, as well as information about the Institute, are available from the NICHD Web site, http://www.nichd.nih.gov, or from the NICHD Information Resource Center, 1-800-370-2943; e-mail NICHDInformationResourceCenter@mail.nih.gov.