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Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene .
Frequently a few adjacent origins open up to duplicate a segment of a chromosome, followed some time later by another group of origins opening up in an adjacent segment. Replication does not necessarily start at exactly the same origin sites every time, but the segments appear to replicate in the same temporal sequence regardless of exactly ...
The underlying mutational event of duplication may be a conventional gene duplication mutation within a chromosome, or a larger-scale event involving whole chromosomes or whole genomes . A classic view, owing to Susumu Ohno , [ 1 ] which is known as Ohno model, he explains how duplication creates redundancy, the redundant copy accumulates ...
Overview of chromosome duplication in the cell cycle. Assembly of the pre-replication complex only occurs during late M phase and early G1 phase of the cell cycle when cyclin-dependent kinase (CDK) activity is low. This timing and other regulatory mechanisms ensure that DNA replication will only occur once per cell cycle.
Before this stage occurs, each chromosome is duplicated , and the two copies are joined by a centromere—resulting in either an X-shaped structure if the centromere is located equatorially, or a two-armed structure if the centromere is located distally; the joined copies are called 'sister chromatids'.
In fast-growing bacteria, such as E. coli, chromosome replication takes more time than dividing the cell. The bacteria solve this by initiating a new round of replication before the previous one has been terminated. [57] The new round of replication will form the chromosome of the cell that is born two generations after the dividing cell.
A chromatid (Greek khrÅmat-'color' + -id) is one half of a duplicated chromosome.Before replication, one chromosome is composed of one DNA molecule. In replication, the DNA molecule is copied, and the two molecules are known as chromatids. [1]
Because each resultant daughter cell should be genetically identical to the parent cell, the parent cell must make a copy of each chromosome before mitosis. This occurs during the S phase of interphase. [33] Chromosome duplication results in two identical sister chromatids bound together by cohesin proteins at the centromere.