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crossing over

(Encyclopedia)crossing over, process in genetics by which the two chromosomes of a homologous pair exchange equal segments with each other. Crossing over occurs in the first division of meiosis. At that stage each ...

equinox

(Encyclopedia)equinox ēˈkwĭnŏks [key], either of two points on the celestial sphere where the ecliptic and the celestial equator intersect. The vernal equinox, also known as “the first point of Aries,” is t...

chord, in geometry

(Encyclopedia)chord kôrd [key], in geometry, straight line segment both end points of which lie on the circumference of a circle or other curve; it is a segment of a secant. A chord passing through the center of a...

Nikopol, city, Ukraine

(Encyclopedia)Nikopol nyĭkôˈpəl [key], city (1989 pop. 158,000), SE Ukraine, on the Dnieper River. It is a rail terminus and the industrial center of one of the world's richest manganese-mining areas. The city ...

Sulaiman Mountains

(Encyclopedia)Sulaiman Mountains so͞olīmänˈ [key], range, extending c.250 mi (400 km) from N to S along the western edge of the Indus River valley in E Baluchistan province, central Pakistan. The twin peaks of ...

tidewater

(Encyclopedia)tidewater, in U.S. history, that part of the Atlantic coastal plain between the shoreline and the farthest upstream points in rivers reached by oceanic tides. In many cases the fall line is given as t...

midnight sun

(Encyclopedia)midnight sun, phenomenon in which the sun remains visible in the sky continuously for 24 hr or longer, occurring only in the polar regions. The midnight sun is due to the fact that the plane of the ea...

Lorentz, Hendrik Antoon

(Encyclopedia)Lorentz, Hendrik Antoon hĕnˈdrək änˈtōn lōˈrĕnts [key], 1853–1928, Dutch physicist, a pioneer in formulating the relations between electricity, magnetism, and light. He was one of the first...

Gongga

(Encyclopedia)Gongga mĭnˈyə kŏngˈkə [key], peak, 24,900 ft (7,590 m) high, SW Sichuan prov., central China, in the Daxue Mts.; one of the highest points in China. It was climbed (1932) by an American expediti...

Cartesian coordinates

(Encyclopedia)CE5 Cartesian coordinates Cartesian coordinates kärtēˈzhən [key] [for René Descartes], system for representing the relative positions of points in a plane or in space. In a plane, the point P...