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 condition whereby either the spinal canal (central stenosis) or vertebral foramen (foraminal stenosis) becomes narrowed, leading to compression of the spinal nerves. Symptoms are pain in the lower back and weakness, numbness, pain, and loss of sensation in the legs. The most common cause of lumbar spinal stenosis is degenerative arthritis (osteoarthritis), but other […]

Family, gene: A group of genes related in structure and often in function. The genes belonging to a gene family are descended from an ancestral gene. For example, the hemoglobin genes of critical importance to red blood cells belong to one gene family created by gene duplication (making extra copies of a gene) and divergence […]

A complex molecule that contains both protein and sugar. Lectins are made by both animals and plants and are able to bind to the outside of a cell and cause biochemical changes in it.

In the ventricle of the heart or the brain.

Biotin: A water-soluble B-complex vitamin involved in carbon dioxide transfer and therefore essential to the metabolism of carbohydrate and fat. A balanced diet usually contains enough biotin. Foods with high biotin levels include nuts, cereals, green leafy vegetables and milk. Biotin deficiency, which is characterized by hair loss and a scaly red rash, can occur […]