cleavage

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The Constitution of the Cleavage

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For more information on cleavage, visit Britannica.com.

The subdivision of eggs into cells called blastomeres. It occurs in eggs activated by fertilization or parthenogenetic agents. Cleavages follow one another so rapidly that there is little opportunity for daughter cells to grow before they divide again. Consequently the size of blastomeres diminishes progressively, although many times unequally, during cleavage. By contrast, the nucleus of each daughter cell enlarges following each cleavage with the result that the ratio of the volume of the nucleus to the volume of cytoplasm (the nucleoplasmic ratio) progressively increases. The cleavage period is said by some authorities to terminate when the nucleoplasmic ratios of various blastomeres attain values characteristic of adult tissues. Cells continue to divide thereafter, but each daughter cell then undergoes a period of growth prior to its division with the result that the nucleoplasmic ratio tends to remain approximately constant for each cell type following termination of cleavage. According to others, cleavage terminates with formation of the definitive blastula. Cleavage appears to be an essential step in development. Although some differentiation occurs in eggs of certain animals when cleavage is blocked experimentally, it is limited and infrequent. See also Blastulation.

Cleavage does more than merely subdivide the substance of the egg quantitatively into smaller units, the blastomeres, which are then of such a size that they can readily undergo the subsequent events of blastulation, gastrulation, and interaction that are involved in formation of tissues and organs. Sooner or later, cleavage segregates different cytoplasmic areas into different blastomeres, thus subdividing the substance of the egg qualitatively. These qualitative cytoplasmic differences among blastomeres are then sufficient to account for the initial establishment of different lines of differentiation in the progeny of different blastomeres, even though the genetic content of all blastomeres is identical. See also Cell lineage.

noun

A usually narrow partial opening caused by splitting and rupture: break, chink, cleft, crack, crevice, fissure, rift, split. See open/close.

1. A division in society due to political or partisan allegiance. Examples include: Yankee versus Confederate in the American Civil War, revolutionaries versus the ancien régime in the French Revolution, or workers versus bosses.

2. The ability of a rock to split along a cleavage plane.

Term borrowed from its geological meaning to denote the splitting of a political system along ethnic or ideological lines. The term is used rather loosely, sometimes to indicate the division between dimensions (as in ‘cleavage structure’), sometimes just as a synonym for disagreement within a dimension.

1. In rocks, a tendency to split along parallel, generally closely spaced surfaces as, for example, in slate.
2. In some stone industries, the splitting along the depositional layering.
3. The rupturing of adhesive bonds between rigid materials; a prying action.
4. A tendency in some woods to split along closely spaced parallel planes, as in shingles.

The process by which an animal cell divides into two daughter cells after mitosis. In an embryo, this process is repeated many times and leads to the formation of the blastula.

1. the tendency of a crystal to split in certain preferred directions with the formation of smooth surfaces, or the act of so splitting a crystal; hence cleavage plane, cleavage face.
2. the rupture of a (usually specified) chemical bond in a molecule with the formation of smaller molecules.
3. or segmentation (in embryology) the series of mitotic divisions by which a fertilized animal ovum changes, without any overall change in size, into a ball of smaller cells constituting the primitive embryo.

1. division into distinct parts, e.g. the double helix.
2. the early successive splitting of a fertilized ovum into smaller cells (blastomeres) by mitosis. See also holoblastic, meroblastic.

• c. site — the places on a strand of DNA where the restriction enzyme cleaves the DNA.

• Aspects and Components of Appearance - cleavage: area between a woman’s breasts
• Reproduction and Development - cleavage: progressive subdivision of zygote by mitotic cell division
• Processes, Phenomena, Events, and Techniques - cleavage: pattern of breakage of rock or minerals along flat planes
• Fashion, Trim, and Sewing - cleavage: revealing hollow between woman’s breasts, esp. when revealed by low-cut neckline
• Anatomy and Physiology of Sex - cleavage: area between woman’s breasts

Look up cleavage in Wiktionary, the free dictionary.

Cleavage may refer to:

• Cleavage (breasts), partial exposure of the separation between a woman's breasts.
  • Cleavage enhancement, methods of making a person's breast cleavage look more substantial than it really is.
• Buttock cleavage, minor exposure of the buttocks and the gluteal cleft between them
• Toe cleavage, partial exposure of a woman's toes in shoes
• Cleavage (crystal), in mineralogy and materials science, is a process of splitting a single crystal.
• Cleavage (geology), Foliation perpendicular to stress as a result of ductile deformation. e.g. shales (shists)
• Cleavage (embryo), in embryology, is the division of cells in the early embryo.
• Cleavage (fiber), in optical fibers.
• Teeth cleavage or tooth cleavage, slang for Diastema (dentistry), the gap between a person's two front teeth.
• In cell biology, the Cleavage furrow is the indentation that begins the process of cleavage, by which animal cells undergo cytokinesis.
• Bond cleavage in chemistry and biochemistry
• Cleavage (politics) The divisions of society that cause people to vote differently

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Dansk (Danish)
n. - kløvning, spaltning, splittelse, kavalergang

Nederlands (Dutch)
(cel)scheiding, decolleté, het splijten

Français (French)
n. - décolleté, fendage, fissure, (Biol) division, (Géol) clivage

Deutsch (German)
n. - Spaltung, Kluft, Dekolleté

Ελληνική (Greek)
n. - διαίρεση, κατάτμηση, ρωγμή, σχίσιμο, (ενδυμ.) άνοιγμα του λαιμού, ντεκολτέ, (βιολ.) κατάτμηση, αυλάκωση

Italiano (Italian)
divisione, incavo tra i seni

Português (Portuguese)
n. - corte (m), rachadura (f), desunião (f) (fig.)

Русский (Russian)
расщелина, ложбинка между грудями, раскол

Español (Spanish)
n. - escisión, división, separación

Svenska (Swedish)
n. - klyvning, spaltning, spricka, djup urringning

中文（简体）(Chinese (Simplified))
劈开, 分裂, 劈开部

中文（繁體）(Chinese (Traditional))
n. - 劈開, 分裂, 劈開部

한국어 (Korean)
n. - 쪼개짐, 분열, 의견의 불일치

日本語 (Japanese)
n. - 裂開, 分裂, 卵割

العربيه (Arabic)
‏(الاسم) شق, فطر, انشقاق‏

עברית (Hebrew)
n. - ‮חריץ בין השדיים, חלוקה, התבקעות, הסתדקות, התפצלות תא‬

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