accessory chromosome (B chromosome; supernumerary chromosome) Any chromosome that is additional to the regular karyotype of a species. Such chromosomes vary in size and composition and may or may not affect the phenotype. In humans, about one person in every 1500 carries an accessory chromosome, and some of these are associated with mental or physical abnormalities. For example, cat-eye syndrome occurs in people who carry an extra chromosome that partly duplicates chromosome 22. It is characterized by enlarged pupils, skin malformations, cardiac and urinary defects, and, sometimes, mental handicap.
More From encyclopedia.com
Tsetse Flies , Glossinidae (tsetse fly; order Diptera, suborder Cyclorrapha) Family of flies which are well known as important carriers of disease organisms, e.g. t… Toad , toad, name applied to certain members of the amphibian order Anura, which also includes the frog. Although there is no clear-cut distinction between… Cretinism , cretinism Underactivity of the thyroid gland (hypothyroidism) in children, resulting in poor growth, severe mental retardation and deafness. Commonly… Albinism , Albinism is a recessive inherited defect in melanin metabolism in which pigment is absent from hair, skin, and eyes (oculocutaneous albinism) or just… Vitiligo , Vitiligo is a condition that causes white patches of skin due to a loss of pigment in the cells and tissues of the body. KEYWORDS for searching the I… Amphibia , Amphibia is one of the five major classes of vertebrates. There are three orders in the amphibia group, two of which are widely familiar, frogs (Anur…
Updated About encyclopedia.com content Print Article
You Might Also Like