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 […]

A rare type of chronic leukemia in which the abnormal white blood cells appear to be covered with tiny hairs when examined microscopically. The hairy cells are malignant B lymphocytes. There may be too few normal blood cells of all types because of an excess of leukemic cells in the bone marrow. The deficit of […]

The male external genitalia — the penis, the male urethra, and the scrotum; and The male internal genitalia — the testis, epididymis, ductus deferens, seminal vesicle, ejaculatory duct, bulbourethral gland, and the prostate. In the male, the external genitalia are more evident and better known than in the female. The converse may be true with […]

A maneuver in which one tries with force to exhale with the windpipe closed, impeding the return of venous blood to the heart.

RNA inactivation; and RNA interference.

A type of personality characterized by unusual patterns of speech and behavior and by social withdrawal. See also Asperger syndrome.