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 […]

Drug resistance: The ability of bacteria and other microorganisms to withstand a drug that once stalled them or killed them.

Adjuvant: A substance that helps and enhances the effect of a drug, treatment, or biologic system.

The set of 20 first (deciduous) teeth. The primary dentition is as opposed to the secondary (permanent) dentition. At birth, both sets of dentition are evident by X-ray.

Cranial nerve II: The second cranial is the optic nerve, the nerve that connects the eye to the brain and carries the impulses formed by the retina — the nerve layer that lines the back of the eye, senses light and creates the impulses — to the brain which interprets them as images. The cranial […]

Collagen disease: A disease that damages collagen or other components of connective tissue. For example, dermatomyositis and systemic lupus erythematosus are collagen diseases.