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 downy hair on the body of the fetus and newborn baby. The lanugal hair (or lanugo) is the first hair to be produced by the fetal hair follicles. It is very fine, soft and usually is unpigmented. The lanugal hair is prenatal hair. It appears at about 5 months of gestation and begins to […]

See Popliteal web syndrome.

Red corpuscles are cells that carry oxygen in the blood. They are also called red blood cells or “RBCs.”

Carotid body: A small “body” of tissue rich in capillaries, at the spot the carotid artery branches in the neck, containing cells that sense the oxygen and carbon dioxide levels in blood and from which messages are dispatched to the medulla (in the brain) to regulate the heart rate.

In medicine, to introduce a solution into the body through a vein. An infusion is the therapeutic introduction of a fluid other than blood into a vein. The infused fluid might, for example, be a saline (salt) solution.