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 […]

Holmes, Oliver Wendell, Sr.

A substance made by cells that stimulates new blood vessel formation, a mitogen for vascular endothelial (vessel lining) cells. VEGF is a polypeptide structurally related to platelet-derived growth factor (PDGF). The gene for VEGF is on chromosome 6p12.

COPD. Any disorder that persistently obstructs bronchial airflow. COPD mainly involves two related diseases — chronic bronchitis and emphysema. Both cause chronic obstruction of air flowing through the airways and in and out of the lungs. The obstruction is generally permanent and progresses (becomes worse) over time. Asthma is also a pulmonary disease in which […]

Surgery can also help fluid escape from the eye and thereby reduce the pressure. However, surgery is now usually reserved for patients whose pressure cannot be controlled with eyedrops, pills, or laser surgery.

Ball-and-socket joint: A joint in which the round end of a bone fits into the cavity of another bone. The hip joint is a ball-and-socket joint.