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An inversion is a chromosome rearrangement in which a segment of a chromosome becomes inverted within its original position. An inversion occurs when a chromosome undergoes a two breaks within the chromosomal arm, and the segment between the two breaks inserts itself in the opposite direction in the same chromosome arm.
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The classical example is the Drosophila w m4 (speak white-mottled-4) translocation.In this mutation, an inversion on the X chromosome placed the white gene next to pericentric heterochromatin, or a sequence of repeats that becomes heterochromatic. [3]
This is called circle inversion or plane inversion. The inversion taking any point P (other than O ) to its image P ' also takes P ' back to P , so the result of applying the same inversion twice is the identity transformation which makes it a self-inversion (i.e. an involution).
Hence, in hindsight, the first observation of neocentromeres made by Andy Choo in 1997 was most likely an example of a Class II pericentric interstitial deletion, followed by a complex rearrangement. The neocentromere can either appear on the linear chromosome or on the ring chromosome, depending on which ever one lacks a centromere.
A hypercentric or pericentric lens is a lens system where the entrance pupil is located in front of the lens, in the space where an object could be located. In a certain region, objects that are further away from the lens produce larger images than objects that are closer to the lens.
A Robertsonian translocation. The short arms of the chromosomes (shown on right) are often lost . Robertsonian translocation (ROB) is a chromosomal abnormality where the entire long arms of two different chromosomes become fused to each other.
A dicentric chromosome is an abnormal chromosome with two centromeres.It is formed through the fusion of two chromosome segments, each with a centromere, resulting in the loss of acentric fragments (lacking a centromere) and the formation of dicentric fragments. [1]