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Mitosis (/ m aɪ ˈ t oʊ s ɪ s /) is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis is an equational division which gives rise to genetically identical cells in which the total number of chromosomes is maintained. [1]
A karyotype of an individual with trisomy 21, showing three copies of chromosome 21. An abnormal number of chromosomes is known as aneuploidy, and occurs when an individual is either missing a chromosome from a pair (resulting in monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.).
Cancers can go through periods of extreme instability where chromosome number can vary within the population. Rapid chromosomal instability is thought to be caused by telomere erosion. However, the period of rapid change is transient as tumor cells generally reach an equilibrium abnormal chromosome content and number. [20]
The thick lines are chromosomes, and the thin blue lines are fibers pulling on the chromosomes and pushing the ends of the cell apart. The cell cycle in eukaryotes: I = Interphase, M = Mitosis, G 0 = Gap 0, G 1 = Gap 1, G 2 = Gap 2, S = Synthesis, G 3 = Gap 3. Cell division is the process by which a parent cell divides into two daughter cells. [1]
These divide by a special process that reduces the number of chromosomes by a half. This initially results in four single-celled haploid spores, each containing n unpaired chromosomes. [17] The single-celled haploid spore germinates, dividing by the normal process (mitosis), which maintains the number of chromosomes at n.
Anaphase lag is a consequence of an event during cell division where sister chromatids do not properly separate from each other because of improper spindle formation. [1] The chromosome or chromatid does not properly migrate during anaphase and the daughter cells will lose some genetic information.
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). In genetics , a chromosomal rearrangement is a mutation that is a type of chromosome abnormality involving a change in the structure of the native chromosome . [ 1 ]
Changes in chromosome number may involve even larger mutations, where segments of the DNA within chromosomes break and then rearrange. For example, in the Homininae, two chromosomes fused to produce human chromosome 2; this fusion did not occur in the lineage of the other apes, and they retain these separate chromosomes. [21]