Glossary 
153 
Primitive streak: A band of cells appearing in the embryo at the 
start of the third week of development, that marks the axis along 
which the spinal chord develops. 
Primordial germ cell: A gamete, that is, a sperm or egg, OR a pri- 
mordial cell that can mature into a sperm or egg. (NRG) 
Salivary gland: One of several pairs of glands in the mouth that se- 
crete saliva. 
Skin biopsy: Process of removing tissue, in this case skin, from living 
patients for diagnostic examination, or the tissue specimen obtained 
by that process. (SMD) 
“Single-cell cloned”: A procedure pertaining to cells in vitro in 
which the descendants of a single cell are physically isolated from 
other cells growing in a dish, and then expanded into a larger popu- 
lation. 
Somatic cell nuclear transfer (SCNT): A method of cloning: transfer 
of the nucleus from a donor somatic cell into an enucleated egg to 
produce a cloned embryo. 
Somite: One of the longitudinal series of segments into which the 
body of many animals (including vertebrates) is divided. (Merriam- 
Webster on line) 
Stem cells: Stem cells are undifferentiated multipotent precursor 
cells that are capable both of perpetuating themselves as stem cells 
and of undergoing differentiation into one or more specialized types 
of cells. (OR) 
Stromal: Relating to the stroma of an organ or other structure, that is, 
its framework, usually of connective tissue, rather than its specific 
substance. (SMD) 
Syngamy: The coming together of the egg and sperm at fertilization. 
Thymus: An organ of the developing immune system, active mainly 
in childhood. 
T-lymphocyte: A cell type of the immune system that matures in the 
thymus and is responsible for cell-mediated immunity. 
PRE -PUBLICATION VERSION 
