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The third documented type of gene dose regulatory mechanism is incomplete compensation without balance (sometimes referred to as incomplete or partial dosage compensation). In this system gene expression of sex-specific loci is reduced in the heterogametic sex i.e. the females in ZZ/ZW systems and males in XX/XY systems. [4]
Humans typically have a gene dosage of two. Because they are diploid, they have two sets of 23 different chromosomes. The number of copies of chromosomes generally correlates to the number of copies of a gene present in the genome. For example, the gene that codes for the beta-subunit of hemoglobin (HBB) is located on chromosome 11.
The existence of genes along the inactive X which are not silenced explains the defects in humans with atypical numbers of the X chromosome, such as Turner syndrome (X0, caused by SHOX gene [43]) or Klinefelter syndrome (XXY). Theoretically, X-inactivation should eliminate the differences in gene dosage between affected individuals and ...
X chromosome reactivation (XCR) is the process by which the inactive X chromosome (the Xi) is re-activated in the cells of eutherian female mammals. Therian female mammalian cells have two X chromosomes, while males have only one, requiring X-chromosome inactivation (XCI) for sex-chromosome dosage compensation.
Since humans have many more genes on the X than the Y, there are many more X-linked traits than Y-linked traits. However, females carry two or more copies of the X chromosome, resulting in a potentially toxic dose of X-linked genes. [4] To correct this imbalance, mammalian females have evolved a unique mechanism of dosage compensation.
Hyperactivation is a term also used to express an X chromosome gene dosage compensation mechanism and is seen in Drosophila. Here, a complex of proteins bind to the X-linked genes to effectively double their genetic activity. This allows males (XY) to have equal genetic activity as females (XX), whose X's are not hyperactivated.
7503 213742 Ensembl ENSG00000229807 ENSMUSG00000086503 UniProt n a n/a RefSeq (mRNA) n/a n/a RefSeq (protein) n/a n/a Location (UCSC) Chr X: 73.82 – 73.85 Mb Chr X: 102.5 – 102.53 Mb PubMed search Wikidata View/Edit Human View/Edit Mouse Xist (X-inactive specific transcript) is a non-coding RNA transcribed from the X chromosome of the placental mammals that acts as a major effector of the ...
In 2007, a time where there had not been extensive research on other organisms with the ZW sex-determination system, researchers announced that chickens' and zebra finches' sex chromosomes do not exhibit any type of chromosome-wide dosage compensation, and instead seem to dosage compensate on a gene-by-gene basis.