X inactivation

Examples of X inactivation in the following topics:

• X-Inactivation

  • The presence of extra X chromosomes in a cell is compensated for by X-inactivation in which all but one X chromosome are silenced.
  • In part, this occurs because of a molecular process called X inactivation.
  • So how does X-inactivation help alleviate the effects of extra X chromosomes?
  • If three X chromosomes are present, the cell will inactivate two of them.
  • If four X chromosomes are present, three will be inactivated, and so on.

• Sex-Linked Traits

  • When a gene being examined is present on the X chromosome, but not on the Y chromosome, it is said to be X-linked.
  • Eye color in Drosophila was one of the first X-linked traits to be identified, and Thomas Hunt Morgan mapped this trait to the X chromosome in 1910.
  • Because human males need to inherit only one recessive mutant X allele to be affected, X-linked disorders are disproportionately observed in males.
  • Carrier females can manifest mild forms of the trait due to the inactivation of the dominant allele located on one of the X chromosomes.
  • Eye color in Drosophila is an example of a X-linked trait

• Basic Techniques to Manipulate Genetic Material (DNA and RNA)

  • Macromolecules are inactivated using enzymes such as proteases that break down proteins, and ribonucleases (RNAses) that break down RNA.
  • RNA is naturally very unstable because RNAses are commonly present in nature and very difficult to inactivate.
  • Similar to DNA, RNA extraction involves the use of various buffers and enzymes to inactivate macromolecules and preserve the RNA.

• Termination of the Signal Cascade

  • Phosphorylation adds a phosphate group to serine, threonine, and tyrosine residues in a protein, changing their shapes, and activating or inactivating the protein .

• Methods of Intracellular Signaling

  • Phosphorylation may activate or inactivate enzymes; the reversal of phosphorylation, dephosphorylation by a phosphatase, will reverse the effect.
  • This diagram shows the mechanism for the formation of cyclic AMP (cAMP). cAMP serves as a second messenger to activate or inactivate proteins within the cell.

• Horizontal Gene Transfer

  • Furthermore, it has been shown that when this gene is inactivated by mutation, the aphids revert back to their more common green color .
  • If genes for making carotenoids are inactivated by mutation, the aphids revert back to (b) their green color.

• Physical and Chemical Barriers

  • Pathogens are killed or inactivated on the skin by desiccation (drying out) and by the skin's acidity.

• White Blood Cells

  • B cells destroy bacteria and inactivate their toxins; they also produce antibodies.

• Symbiosis between Bacteria and Eukaryotes

  • Nitrogenase, the enzyme that fixes nitrogen, is inactivated by oxygen, so the nodule provides an oxygen-free area for nitrogen fixation to take place.

• Cell Signaling and Cellular Metabolism

  • This diagram shows the mechanism for the formation of cyclic AMP (cAMP). cAMP serves as a second messenger to activate or inactivate proteins within the cell.