• Z chromosome

    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.

  • ZAP-70

    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 […]

  • Zebra

    ‘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.

  • Zygotic lethal gene

    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 […]

  • Zygote intrafallopian transfer (ZIFT)

    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 […]

  • Arthrogryposis

    Arthrogryposis: Joint contractures that develop before birth and are evident at birth. With arthrogryposis there is a lack of the normal range of motion in one or more joints. In normal embryonic development, joints can be seen moving by 8 weeks of gestation. This motion of joints is essential to the proper development of the […]

  • Concordant couple

    Concordant couple: A pair of long-term sexual partners in which both partners have a sexually transmitted infection. The CDC has guidelines for counseling concordant couples in which both the man and woman are HIV-infected.

  • Preconceptual counselling

    The interchange of information prior to pregnancy. Usually for pregnancy planning and care, but sometimes in the form of genetic counseling. See also genetic counseling.

  • DNA, repetitive

    DNA, repetitive: DNA sequences that are repeated in the genome. These sequences do not code for protein. One class termed highly repetitive DNA consists of short sequences, 5-100 nucleotides, repeated thousands of times in a single stretch and makes up satellite DNA. Another class termed moderately repetitive DNA consists of longer sequences, about 150-300 nucleotides, […]

  • Mastocytosis

    Mastocytoma — A benign nodular tumor on the skin rich in mast cells. Usually present at birth or in early childhood and resolves spontaneously. Also called a mast cell tumor. Urticaria pigmentosa — The most common form of mastocytosis consisting of small aggregations of mast cells within characteristic salmon-brown patches of ski which itch when […]