Introduction to genetics: Difference between revisions

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==Inherited diseases==

Some diseases are hereditary and run in families; others, such as [[infectious disease]]s, are caused by the environment. Other diseases come from a combination of genes and the environment.<ref>[http://www.genome.gov/19016930 requently Asked Questions About Genetic Disorders] NIH, Accessed 20 May 2008</ref> [[Genetic disorder]]s are diseases that are caused by aone singleor allelemore ofabnormalities ain genethe genome and are inherited in families. These may be monogenic (caused by alterations in a single gene), polygenic (caused by alterations in multiple genes). Examples of monogenic gene disorders include [[Huntington's disease]], [[cystic fibrosis]] or [[Duchenne muscular dystrophy]]. Cystic fibrosis, for example, is caused by mutations in a single gene calledthe ''[[CFTR (gene)|CFTR]]'' gene and is inherited as a recessive trait.<ref>[https://web.archive.org/web/20030801073139/http://ghr.nlm.nih.gov/condition=cysticfibrosis Cystic fibrosis] Genetics Home Reference, NIH, Accessed 16 May 2008</ref>

Other diseases are influenced by genetics, but the genes a person gets from their parents only change their risk of getting a disease. Most of these diseases are inherited in a complex way, with either multiple genes involved, or coming from both genes and the environment. As an example, the risk of [[breast cancer]] is 50 times higher in the families most at risk, compared to the families least at risk. This variation is probably due to a large number of alleles, each changing the risk a little bit.<ref>{{cite journal |author=Peto J |title=Breast cancer susceptibility&nbsp;– A new look at an old model |journal=Cancer Cell |volume=1 |issue=5 |pages=411–2 |date=June 2002 |pmid=12124169 |doi=10.1016/S1535-6108(02)00079-X |issn=1535-6108|doi-access=free }}</ref> Several of the genes have been identified, such as ''[[BRCA1]]'' and ''[[BRCA2]]'', but not all of them. However, although some of the risks are genetic, the risk of this cancer is also increased by being overweight, heavy alcohol consumption and not exercising.<ref>[http://www.cancer.org/docroot/CRI/content/CRI_2_4_2X_What_are_the_risk_factors_for_breast_cancer_5.asp What Are the Risk Factors for Breast Cancer?] {{webarchive|url=https://web.archive.org/web/20090429042057/http://www.cancer.org/docroot/CRI/content/CRI_2_4_2X_What_are_the_risk_factors_for_breast_cancer_5.asp |date=29 April 2009 }} American Cancer Society, Accessed 16 May 2008</ref> A woman's risk of breast cancer, therefore, comes from a large number of alleles interacting with her environment, so it is very hard to predict.

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==Genetic engineering==

{{main|Genetic engineering}}

Since traits come from the genes in a cell, putting a new piece of DNA into a cell can produce a new trait. This is how [[genetic engineering]] works. For example, rice can be given genes from a maize and a soil bacteria so the rice produces [[beta-carotene]], which the body converts to vitamin A.<ref>Staff [http://www.goldenrice.org/ Golden Rice Project] Retrieved 5 November 2012</ref> This can help children with Vitamin A deficiency. Another gene being put into some crops comes from the bacterium ''[[Bacillus thuringiensis]]''; the gene makes a protein that is an [[insecticide]]. The insecticide kills insects that eat the plants but is harmless to people.<ref>[https://agresearchmag.ars.usda.gov/1999/nov/pest Tifton, Georgia: A Peanut Pest Showdown] USDA, accessed 16 May 2008</ref> In these plants, the new genes are put into the plant before it is grown, so the genes are in every part of the plant, including its seeds.<ref>[http://www.gmo-safety.eu/basic-info/129.bacterial-arsenal-combat-chewing-insects.html Genetic engineering: Bacterial arsenal to combat chewing insects] {{Webarchive|url=https://web.archive.org/web/20110515134013/http://www.gmo-safety.eu/basic-info/129.bacterial-arsenal-combat-chewing-insects.html |date=15 May 2011 }} GMO Safety, Jul 2010</ref> The plant's offspring inherit the new genes, which has led to concern about the spread of new traits into wild plants.<ref>[httphttps://www.geo-pie.cornell.edu/gmo.html Genetically engineered organisms public issues education] Cornell University, Accessed 16 May 2008</ref>

The kind of technology used in genetic engineering is also being developed to treat people with [[genetic disorder]]s in an experimental medical technique called [[gene therapy]].<ref>{{cite web| last = Staff|date= November 18, 2005| url = http://www.ornl.gov/sci/techresources/Human_Genome/medicine/genetherapy.shtml| title = Gene Therapy| format = FAQ| work = Human Genome Project Information| publisher = [[Oak Ridge National Laboratory]]| access-date = 2006-05-28}}</ref> However, here the new, properly working gene is put in targeted cells, not altering the chance of future children inheriting the disease causing alleles.