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Mitosis divides the chromosomes in a cell nucleus. During mitosis chromosome segregation occurs routinely as a step in cell division (see mitosis diagram). As indicated in the mitosis diagram, mitosis is preceded by a round of DNA replication, so that each chromosome forms two copies called chromatids.
Waddington called the effect he had seen "genetic assimilation". His explanation was that it was caused by a process he called "canalization".He compared embryonic development to a ball rolling down a slope in what he called an epigenetic landscape, where each point on the landscape is a possible state of the organism (involving many variables).
Mitosis is the normal process in eukaryotes for cell division; duplicating chromosomes and segregating one of the two copies into each of the two daughter cells, in contrast with meiosis. The mitosis theory states that meiosis evolved from mitosis. [9]
This is an accepted version of this page This is the latest accepted revision, reviewed on 5 January 2025. Cell division producing haploid gametes For the figure of speech, see Meiosis (figure of speech). For the process whereby cell nuclei divide to produce two copies of themselves, see Mitosis. For excessive constriction of the pupils, see Miosis. For the parasitic infestation, see Myiasis ...
The grasshopper Melanoplus femur-rubrum was exposed to an acute dose of X-rays during each individual stage of meiosis, and chiasma frequency was measured. [23] Irradiation during the leptotene-zygotene stages of meiosis (that is, prior to the pachytene period in which crossover recombination occurs) was found to increase subsequent chiasma ...
During G 2, the cell undergoes the final stages of growth before it enters the M phase, where spindles are synthesized. The M phase can be either mitosis or meiosis depending on the type of cell. Germ cells, or gametes, undergo meiosis, while somatic cells will undergo mitosis. After the cell proceeds successfully through the M phase, it may ...
When a heterozygote creates gametes by meiosis, the alleles normally duplicate and end up in a 2:2 ratio in the resulting 4 cells that are the direct products of meiosis. However, in gene conversion, a ratio other than the expected 2A:2a is observed, in which A and a are the two alleles.
In meiosis II, a peculiarity occurs with the X chromosome. Normally, in meiosis II (as in mitosis), all chromosomes are divided into the two chromatids that make them up and these are allocated to the two daughter nuclei. In fungus gnats, on the other hand, the X chromosome travels prematurely to one of the spindle poles and only divides there ...