Other factors include the loss of methylation, increasing gene expression heterogeneity correlating to genomic abnormalities, and telomere shortening. Įarly research on somatic mutations in aging showed that deletions, inversion, and translocations of genetic material are common in aging mice and aging genomes tend to contain visible chromosomal changes, mitotic recombination, whole gene deletions, intragenic deletions, and point mutations. Somatic variations during embryonic development can be represented by monozygous twins since they carry different copy number profiles and epigenetic marks that keep on increasing with age. But these are uncommon in somatic cells because they are usually selected against due to their deleterious consequences. Genetic alterations involving gains or loss of entire chromosomes predominantly occur during anaphase stage of cell division. Yet not all somatic mutations are propagated to the adult individual, due to the phenomenon of cell competition. Novel array based techniques for screening genome-wide copy number variants and loss of heterozygosity in single cells showed that chromosome aneuploidies, uniparental disomies, segmental deletions, duplications, and amplifications frequently occur during embryogenesis. These alterations within somatic cells begin at an early stage (pre- implantation or conception) and continue during aging, giving rise to phenotypic heterogeneity within cells, which may lead to the development of diseases such as cancer. Somatic mosaicism arises a result of somatic mutations: genomic (or even mitochondrial) alterations of different sizes ranging from a single nucleotide to chromosome gains or loss within somatic cells. Somatic mosaicism in healthy human tissues Genetic mutations involved in mosaicism may be due to endogenous factors, such as transposons and ploidy changes, or exogenous factors, such as UV radiation and nicotine. Occurrence of this phenomenon not only can result in major phenotypic changes but also reveal the expression of otherwise lethal genetic mutations. In biological systems, mosaicism implies the presence of more than one genetically distinct cell line in a single organism. At a distance, the collective image appears as it would in a painting only on close inspection do the individual components become recognizable. The term mosaic (from medieval Latin musaicum, meaning "work of the Muses") has been used since antiquity to refer to an artistic patchwork of ornamental stones, glass, gems, or other precious material. These variations can lead either to pathogenic phenotypes or not, even if their function in healthy conditions is not completely clear yet. Human somatic variations are somatic mutations ( mutations that occur in somatic cells) both at early stages of development and in adult cells.
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