Where does cleavage collide?

The series of rapid cell divisions that partitions a fertilized egg into smaller cells without any overall growth, so that the single large zygote becomes a cluster of many small blastomeres. O'Farrell, Stumpff, and Su's 2004 Embryonic cleavage cycles: how is a mouse like a fly? described how these early cycles run on stored maternal materials, skip the usual growth phases, and are unusually fast and synchronous. The referent is a developmental process that multiplies cells inside an embryo, counted as division cycles, and it is not the splitting of a crystal, the breaking of a chemical bond, or a division running through a society.[1]

Unit

The number and timing of cleavage divisions from the zygote, counted as cell cycles

Recovery means

Not applicable

Measured by

Observed by microscopy of the dividing embryo, counting blastomeres and timing successive cleavage cycles

The tendency of a crystalline mineral to break along flat, parallel planes where the bonding across the structure is weakest, giving smooth surfaces set at characteristic angles. Klein and Dutrow's 2007 Manual of mineral science treats cleavage as a diagnostic property, described by the direction, number, and quality of these planes and the angles between them. The referent is a physical property of a solid crystal, read from how it splits, and it has nothing to do with the divisions of an embryo, the breaking of one chemical bond, or a rift running through a population.[2]

Unit

A crystal's tendency to split along planes, described by direction and quality

Recovery means

Not applicable

Measured by

Assessed by the number, direction, and quality of cleavage planes and the angles between them, under a hand lens or microscope

A durable division of a society into opposed groups that structures political conflict, such as the splits between workers and owners, church and state, or centre and periphery. Lipset and Rokkan's 1967 Cleavage structures, party systems, and voter alignments argued that a few historical cleavages, laid down by national and industrial revolutions, came to organize party systems and to align voters for generations. The referent is a lasting social and political fault line between groups, read from history and survey data, and it is not a phase of embryonic division, a plane in a crystal, or a broken chemical bond.[3]

Unit

A durable social division aligned with political conflict, described by the groups it separates

Recovery means

Not applicable

Measured by

Traced through survey data, party systems, and the historical alignment of groups by class, religion, region, or centre and periphery