Mutations and stem cells GapFill

Gene mutations, which may arise spontaneously or during DNA replication, are changes to one or more  phospholipidsnucleotideschromosomesphosphates in a sequence. The background mutation rate is fairly low and constant, but the rate may be increased by mutagenic agents, including chemicals or  magnetising radiationvectorsionising radiationfungi. Some mutations can render a resulting polypeptide non-functional and have huge effects on an organism's phenotype; for example, a single base  deletionmethylationacetylationreplacement near the start of a sequence can cause a frame shift so that all the downstream triplets change. Others, such as a base substitution, may not have any effect because the genetic code is  degenerateuniversalfail-safeancient (and most  ribosomesbasesamino acidstriglycerides are coded for by more than one codon). Other mutations may affect a segment of a sequence, e.g. during  an inversiona translocationa deletiona referral, a section of DNA is moved to a different position and inserted there, and during  a deletiona duplicationan additionan inversion, a group of bases is reinserted in the same location but in the reverse order.

Although every body cell arises from a single  zygotecardiomyocyteprokaryotephagocyte and contains the same genetic information, specialisation can occur in multicellular organisms. This is because some  chromatidsgeneshormonesimpulses are not expressed in some cell types, as not all the DNA is translated in every cell. Other cells retain the ability to divide and produce more than one cell type - these are known as stem cells. For example, early in embryonic development, all cells are  unipotenttotipotentomnipotentpolypotent, meaning they can give rise to any type of cell in the human body. As an embryo develops, cells become  pluripotentultrapotentextrapotentmultipotent - they can divide to become almost any cell type, but are slightly more specialised. Adult stem cells, such as those found in the bone marrow, are often  multipotentpluripotentpolypotentquasipotent, so they can produce only a limited number of cell types, or they may be  monopotentunipotentultrapotentinfrapotent, i.e. limited to a single cell type.

Stem cells are important tools in medicine as they can be used to regrow tissues or repair damage resulting from injury or disease. Traditionally,  muscularadultpulmonaryembryonic stem cells were used for this purpose; however, many people have ethical issues with this practice, and research is licensed and heavily controlled. However, scientists are now able to produce  impelled polypotentinduced pluripotentdesigned totipotenteffected pluripotent stem cells from adult cells. These have a number of genes switched on so that they are able to self-renew, and have been used to treat a number of conditions, such as type 1 diabetes.