A sex chromosome in certain animals, such as chickens, turkeys, and moths. In humans, males are XY and females XX, but in animals with a Z chromosome, males are ZZ and females are WZ.

Zeta-chain-associated protein kinase 70. A member of the protein tyrosine kinase family, ZAP-70 is normally expressed in T cells and natural killer cells and has a critical role in the initiation of T-cell signaling. ZAP-70 is expressed in T cells and tumors of T-cell lineage. A high level of ZAP-70 expression appears restricted to T-cell […]

‘When you hear hoof beats, think of horses, not zebras.’ For example, when someone develops a mild transient cough, a virus infection is the most logical and likely cause, and tuberculosis is a zebra.

A gene that is lethal (fatal) for the zygote, the cell formed by the union of a sperm (male sex cell) and an ovum (female sex cell). The zygote would normally develop into an embryo, as instructed by the genetic material within the unified cell. However, a zygotic lethal gene scotches prenatal development at its […]

A technique in which a woman’s egg is fertilized outside the body, then implanted in one of her fallopian tubes. This technique is one of the methods used to overcome infertility, the inability of couples to produce offspring on their own. First, the egg and the male sperm needed to fertilize it are harvested. Then […]

The making of many small, superficial scratches in the skin. Scarification may be done in giving a smallpox vaccination or in removing a tattoo and leaving a scar in its place.

A progressive, inherited disorder of the central nervous system that is caused by a deficiency of the enzyme aspartoacylase. Signs appearing in children between 3 and 6 months of age include developmental delay, significant motor slowness, enlargement of the head (macrocephaly), loss of muscle tone (hypotonia), poor head control, and severe feeding problems. As the […]

Clinical trial: A study that is intended to evaluate the safety and effectiveness of medications or medical devices by monitoring their effects on large groups of people. Studies may be conducted by government health agencies (such as the National Institutes of Health [NIH]), researchers affiliated with hospital or university medical programs, independent researchers, or individuals […]

Oversensitivity of exposed roots of teeth to cold, hot, and sour foods because those roots are no longer protected by healthy gum and bone. Chronic gum disease contributes to toothache due to root sensitivities. The roots are the lower 2/3 of the teeth that are normally buried in bone. The bacterial toxins dissolve the bone […]

Enzymes, yellow: A group of respiratory enzymes that catalyze reactions in the body permitting cells to respire or breathe, in other words, use oxygen. These biochemical reactions are termed oxidation-reduction reactions. The first yellow enzyme was discovered by the German biochemist Otto Heinrich Warburg (1883-1970), a pioneer in research on the respiration of cells, who […]