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The precise structure of the chromatin fiber in the cell is not known in detail. [10] This level of chromatin structure is thought to be the form of heterochromatin, which contains mostly transcriptionally silent genes. Electron microscopy studies have demonstrated that the 30 nm fiber is highly dynamic such that it unfolds into a 10 nm fiber ...
Compare sister chromatids to homologous chromosomes, which are the two different copies of a chromosome that diploid organisms (like humans) inherit, one from each parent. Sister chromatids are by and large identical (since they carry the same alleles, also called variants or versions, of genes) because they derive from one original chromosome.
When a cell is not dividing, chromosomes exist as loosely packed chromatin mesh. [3] The genome of an organism (encoded by the genomic DNA) is the (biological) information of heredity which is passed from one generation of organism to the next. That genome is transcribed to produce various RNAs, which are necessary for the function of the organism.
Chromatin contains the vast majority of the DNA in an organism, but a small amount inherited maternally can be found in the mitochondria. It is present in most cells, with a few exceptions, for example, red blood cells. Histones are responsible for the first and most basic unit of chromosome organization, the nucleosome.
In diploid (2n) organisms, the genome is composed of one set of each homologous chromosome pair, as compared to tetraploid organisms which may have two sets of each homologous chromosome pair. The alleles on the homologous chromosomes may be different, resulting in different phenotypes of the same genes.
This transmission of programming can also alter the chromatin and histone of the DNA and can be passed through the cytosol from parent to offspring during meiosis. [10] Histone modifications in which the structure of chromatin and its transcriptional state is regulated.
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Recombination can be artificially induced in laboratory (in vitro) settings, producing recombinant DNA for purposes including vaccine development. V(D)J recombination in organisms with an adaptive immune system is a type of site-specific genetic recombination that helps immune cells rapidly diversify to recognize and adapt to new pathogens.