Gene dosage

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Gene dosage is the number of copies of a particular gene present in a genome.[1] Gene dosage is known to be related to the amount of gene product the cell is able to express; however, the amount of gene product produced in a cell is more commonly dependent on regulation of gene expression.[2] Nonetheless, changes in gene dosage (copy number variations) due to gene insertions or deletions can have significant phenotypic consequences.[1]

In eukaryotes, most genes found in the cell are expressed as autosomal genes and are found in two copies. Alterations to this two-copy gene dosage are significantly associated with quantitative or qualitative phenotype traits and are linked to many genetic health problems such as those associated with spinal muscular atrophy and Down syndrome.[3] In Down syndrome, the gene expression on chromosome 21 has increased 50%, and this results in significant health and mental disabilities.[4]

Prokaryotes reproduce through asexual reproduction, usually by binary fission. The bacterial chromosome is present only in one copy per cell, but there can still be variation in gene dosage due to DNA replication which starts at the origin of replication and ends at the termination site. The genes that are closer to the origin site are replicated first and are consequently present in two copies in the cell for a longer time than the genes that are closer to the termination site. These slight gene dosage differences are responsible for variation in gene expression depending on the position on the chromosome.[5]

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  1. ^ a b Hartwell LH (2011). Genetics: from genes to genomes (4th ed.). New York: McGraw-Hill. p. 435. ISBN 978-0-07-352526-6.
  2. ^ Garrett RH, Grisham CM, Andreopoulos S, Willmore W, Gallouzi IE (2013), Biochemistry (1st Canadian ed.), Toronto: Nelson Education, pp. 1079–1083, ISBN 978-0-17-650265-2
  3. ^ Nussbaum RL, McInnes RR, Willard HF (2016), Thompson and Thompson Genetics in Medicine, Philadelphia, PA: Elsevier, pp. 64–67, ISBN 978-1-4377-0696-3
  4. ^ Gardiner K (2004-01-01). "Gene-dosage effects in Down syndrome and trisomic mouse models". Genome Biology. 5 (10): 244. doi:10.1186/gb-2004-5-10-244. PMC 545589. PMID 15461808.
  5. ^ Bryant JA, Sellars LE, Busby SJ, Lee DJ (October 2014). "Chromosome position effects on gene expression in Escherichia coli K-12". Nucleic Acids Research. 42 (18): 11383–11392. doi:10.1093/nar/gku828. PMC 4191405. PMID 25209233.