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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.
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.
Inversions that exclude the centromere are known as paracentric inversions, which result in unbalanced gametes after meiosis. [2] During prophase of meiosis I, homologous chromosomes form an inversion loop and crossover occurs. If a paracentric inversion has occurred, one of the products will be acentric, while the other product will be dicentric.
The formation of dicentric chromosomes has been attributed to genetic processes, such as Robertsonian translocation [6] and paracentric inversion. [7] Dicentric chromosomes can have a variety of fates, including mitotic stability. [ 8 ]
A breakage and reunion in the pericentric region of the p arm results in a dicentric isochromosome. [4] Some of the p arm can be found in this formation of i(Xq), but a majority of the genetic material on the p arm is lost so it is considered absent.
Schematic karyogram, with annotated bands and sub-bands as used in the International System for Human Cytogenomic Nomenclature of chromosomal rearrangements. It shows 22 homologous autosomal chromosome pairs, both the female (XX) and male (XY) versions of the two sex chromosomes, as well as the mitochondrial genome (at bottom left).
Among many species of the salamanders, the two chromosomes are only distinguished by a pericentric inversion, so that the banding pattern of the X chromosome is the same as that of Y, but with a region near the centromere reversed.
Also called functionalism. The Darwinian view that many or most physiological and behavioral traits of organisms are adaptations that have evolved for specific functions or for specific reasons (as opposed to being byproducts of the evolution of other traits, consequences of biological constraints, or the result of random variation). adaptive radiation The simultaneous or near-simultaneous ...