Editing Genetics (section)

=== Medicine ===

[[File:Biochemistry, genetics and molecular biology.svg|alt=|thumb|Schematic relationship between [[biochemistry]], genetics and [[molecular biology]]]]

[[Medical genetics]] seeks to understand how genetic variation relates to human health and disease.<ref>{{cite web |url=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=gnd |title=NCBI: Genes and Disease |publisher=NIH: National Center for Biotechnology Information |access-date=15 March 2008 |url-status=dead |archive-url=https://web.archive.org/web/20070220074727/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=gnd&ref=sidebar |archive-date=20 February 2007}}</ref> When searching for an unknown gene that may be involved in a disease, researchers commonly use genetic linkage and genetic [[pedigree chart]]s to find the location on the genome associated with the disease. At the population level, researchers take advantage of [[Mendelian randomization]] to look for locations in the genome that are associated with diseases, a method especially useful for [[Quantitative trait locus|multigenic traits]] not clearly defined by a single gene.<ref>{{cite journal | vauthors = Smith GD, Ebrahim S | title = 'Mendelian randomization': can genetic epidemiology contribute to understanding environmental determinants of disease? | journal = International Journal of Epidemiology | volume = 32 | issue = 1 | pages = 1–22 | date = February 2003 | pmid = 12689998 | doi = 10.1093/ije/dyg070 | doi-access =  | author-link1 = George Davey Smith }}</ref> Once a candidate gene is found, further research is often done on the corresponding (or [[Homology (biology)|homologous]]) genes of model organisms. In addition to studying genetic diseases, the increased availability of genotyping methods has led to the field of [[pharmacogenetics]]: the study of how genotype can affect drug responses.<ref>{{cite web|url=http://www.nigms.nih.gov/Initiatives/PGRN/Background/FactSheet.htm |title=Pharmacogenetics Fact Sheet |access-date=15 March 2008 |publisher=NIH: National Institute of General Medical Sciences |url-status=dead |archive-url=https://web.archive.org/web/20080512012316/http://www.nigms.nih.gov/Initiatives/PGRN/Background/FactSheet.htm |archive-date=12 May 2008}}</ref>

Individuals differ in their inherited tendency to develop [[cancer]], and cancer is a genetic disease. The process of cancer development in the body is a combination of events. Mutations occasionally occur within cells in the body as they divide. Although these mutations will not be inherited by any offspring, they can affect the behavior of cells, sometimes causing them to grow and divide more frequently. There are biological mechanisms that attempt to stop this process; signals are given to inappropriately dividing cells that should trigger [[Apoptosis|cell death]], but sometimes additional mutations occur that cause cells to ignore these messages. An internal process of [[natural selection]] occurs within the body and eventually mutations accumulate within cells to promote their own growth, creating a cancerous [[Tumour heterogeneity|tumor]] that grows and invades various tissues of the body. Normally, a cell divides only in response to signals called [[growth factor]]s and [[Contact inhibition|stops growing once in contact with surrounding cells]] and in response to growth-inhibitory signals. It usually then divides a limited number of times and dies, staying within the [[epithelium]] where it is unable to migrate to other organs. To become a cancer cell, a cell has to accumulate mutations in a number of genes (three to seven). A cancer cell can divide without growth factor and ignores inhibitory signals. Also, it is immortal and can grow indefinitely, even after it makes contact with neighboring cells. It may escape from the epithelium and ultimately from the [[primary tumor]]. Then, the escaped cell can cross the endothelium of a blood vessel and get transported by the bloodstream to colonize a new organ, forming deadly [[metastasis]]. Although there are some genetic predispositions in a small fraction of cancers, the major fraction is due to a set of new genetic mutations that originally appear and accumulate in one or a small number of cells that will divide to form the tumor and are not transmitted to the progeny ([[somatic mutation]]s). The most frequent mutations are a loss of function of [[p53 protein]], a [[tumor suppressor]], or in the p53 pathway, and gain of function mutations in the [[Ras proteins]], or in other [[oncogene]]s.<ref>{{cite journal | vauthors = Frank SA | title = Genetic predisposition to cancer - insights from population genetics | journal = Nature Reviews. Genetics | volume = 5 | issue = 10 | pages = 764–772 | date = October 2004 | pmid = 15510167 | doi = 10.1038/nrg1450 | s2cid = 6049662 }}</ref><ref>{{cite book |vauthors=Strachan T, Read AP |title=Human Molecular Genetics 2 |url=https://archive.org/details/humanmolecularge0002stra |url-access=registration |year=1999 |publisher=John Wiley & Sons Inc. |edition=second}} [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=hmg.chapter.2342 Chapter 18: Cancer Genetics] {{webarchive|url=https://web.archive.org/web/20050926163641/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=hmg.chapter.2342 |date=26 September 2005 }}</ref>