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 […]

Capsid: The protein coat of a virus. The term capsid came in 1960 from the French capside, from the Latin capsa, case. See also: Nucleocapsid.

Airway obstruction; Intestinal obstruction.

The exterior opening to the vagina, the muscular canal that extends from the cervix to the outside of the female body. Also called vaginal introitus and vaginal vestibule.

A break in bone or cartilage. Although usually a result of trauma, a fracture can be the result of an acquired disease of bone, such as osteoporosis, or of abnormal formation of bone in a congenital disease of bone, such as osteogenesis imperfecta (‘brittle bone disease’). Fractures are classified according to their character and location […]

(Or sclero-) A confusing prefix that can refer exclusively to hardness (from the Greek “skleros” meaning hard) but that can also refer to the sclera of the eye. Sclerodactyly, for example, is localized thickening and tightness of the skin of the fingers or toes and scleroderma is disease of connective tissue with the formation of […]