Chromosome X: Difference between revisions
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Chrom<span style="line-height: 1.5em;">osome X is one of the two </span>[[Sex chromosomes|sex-determining chromosomes]]<span style="line-height: 1.5em;"> found in humans and many other animals, | Chrom<span style="line-height: 1.5em;">osome X is one of the two </span>[[Sex chromosomes|sex-determining chromosomes]]<span style="line-height: 1.5em;"> found in humans and many other animals, the other being the </span>[[Y chromosome|Y chromosome]]<span style="line-height: 1.5em;">. In a normal human female, there are two X chromosomes (these are known as </span>[[Homogametic|homogametic]]<span style="line-height: 1.5em;">), and in a normal male there is one X and one Y (these are </span>[[Heterogametic|heterogametic]]<span style="line-height: 1.5em;">)<ref>Ross, MT et al. (2005). The DNA sequence of the human X chromosome. Nature, 434:325-337</ref>.</span> | ||
<span style="line-height: 1.5em;">An X chromosome is much larger than a Y chromosome</span><span style="line-height: 1.5em;">. As human males have only one X chromosome, the likelihood of inheriting an X chromosome linked disease in males is much greater than females. </span> | <span style="line-height: 1.5em;">An X chromosome is much larger than a Y chromosome</span><span style="line-height: 1.5em;">. As human males have only one X chromosome, the likelihood of inheriting an X chromosome linked disease in males is much greater than females. </span> | ||
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Many X chromosome related diseases result from an abnormal number of chromosomes due to [[Nondisjunction|nondisjunction]] during [[Meiosis|meiosis]]. Some examples of these include: | Many X chromosome related diseases result from an abnormal number of chromosomes due to [[Nondisjunction|nondisjunction]] during [[Meiosis|meiosis]]. Some examples of these include: | ||
*[[Klinefelter syndrome|Klinefelter syndrome]] - this is caused by the presence of at least one extra X chromosome in a male [[Karyotype|karyotype]] giving a 47,XXY karyotype or less frequently 48,XXXY, 49,XXXXY and 48,XXYY karyotypes. The extra X chromosome interferes with the males sexual development and reduces levels of testosterone | *[[Klinefelter syndrome|Klinefelter syndrome]] - this is caused by the presence of at least one extra X chromosome in a male [[Karyotype|karyotype]] giving a 47,XXY karyotype or less frequently 48,XXXY, 49,XXXXY and 48,XXYY karyotypes. The extra X chromosome interferes with the males sexual development and reduces levels of testosterone<ref>Who.int, (2014). WHO | Gender and Genetics. [online] Available at: http://www.who.int/genomics/gender/en/index1.html#KlinefelterSyndrome [Accessed 26 Nov. 2014].</ref>. | ||
*[[Turner syndrome|Turner syndrome]] - this is caused by the presence of only one X chromosome giving a 45,X karyotype. This results in altered development, short stature and infertility | *[[Turner syndrome|Turner syndrome]] - this is caused by the presence of only one X chromosome giving a 45,X karyotype. This results in altered development, short stature and infertility<ref>Who.int, (2014). WHO | Gender and Genetics. [online] Available at: http://www.who.int/genomics/gender/en/index1.html#Turnersyndrome [Accessed 26 Nov. 2014].</ref>. | ||
*[[Trisomy X|Trisomy X]] - this is caused by an extra copy of an X chromosome in female cells and gives a 47,XXX karyotype. It shows no obvious characteristics different to the rest of the female population except accelerated growth and speech and language | *[[Trisomy X|Trisomy X]] - this is caused by an extra copy of an X chromosome in female cells and gives a 47,XXX karyotype. It shows no obvious characteristics different to the rest of the female population except accelerated growth and speech and language impairment<ref>Who.int, (2014). WHO | Gender and Genetics. [online] Available at: http://www.who.int/genomics/gender/en/index1.html#XXXFemales [Accessed 26 Nov. 2014].</ref>. | ||
There are also many [[X-linked|X linked]] diseases which can be inherited from parents. If only the mother is affected by the disease (either [[Genotype|genotypcially]] or [[Phenotype|phenotypically]]), a son is more likely to have the disease. This is because they only have one X chromosome so the affected gene will be expressed. A daughter will have a 50% chance of inheriting the disease. If only the father has the disease, 100% of daughters will be carriers as they inherit an X chromosome from each parent. A son will not inherit the disease as they inherit their X chromosomes maternally | There are also many [[X-linked|X linked]] diseases which can be inherited from parents. If only the mother is affected by the disease (either [[Genotype|genotypcially]] or [[Phenotype|phenotypically]]), a son is more likely to have the disease. This is because they only have one X chromosome so the affected gene will be expressed. A daughter will have a 50% chance of inheriting the disease. If only the father has the disease, 100% of daughters will be carriers as they inherit an X chromosome from each parent. A son will not inherit the disease as they inherit their X chromosomes maternally<ref>http://genome.wellcome.ac.uk/doc_WTD020851.html</ref>. | ||
=== | === X chromosome Inactivation === | ||
X chromosome inactivation is the process by which all but one X chromosomes are defunctionalized in a cell and become [[Barr Body|barr bodies]] | [[X chromosome Inactivation|X chromosome inactivation]] is the process by which all but one X chromosomes are defunctionalized in a cell and become [[Barr Body|barr bodies]]<ref>Ahn, J. and Lee, J. (2008) X chromosome: X inactivation. Nature Education, 1(1):24</ref>.<br> | ||
=== References === | === References === | ||
<references /><br> | <references /><br> | ||
Latest revision as of 11:49, 23 November 2018
Chromosome X is one of the two sex-determining chromosomes found in humans and many other animals, the other being the Y chromosome. In a normal human female, there are two X chromosomes (these are known as homogametic), and in a normal male there is one X and one Y (these are heterogametic)[1].
An X chromosome is much larger than a Y chromosome. As human males have only one X chromosome, the likelihood of inheriting an X chromosome linked disease in males is much greater than females.
X Chromosome related illnesses
Many X chromosome related diseases result from an abnormal number of chromosomes due to nondisjunction during meiosis. Some examples of these include:
- Klinefelter syndrome - this is caused by the presence of at least one extra X chromosome in a male karyotype giving a 47,XXY karyotype or less frequently 48,XXXY, 49,XXXXY and 48,XXYY karyotypes. The extra X chromosome interferes with the males sexual development and reduces levels of testosterone[2].
- Turner syndrome - this is caused by the presence of only one X chromosome giving a 45,X karyotype. This results in altered development, short stature and infertility[3].
- Trisomy X - this is caused by an extra copy of an X chromosome in female cells and gives a 47,XXX karyotype. It shows no obvious characteristics different to the rest of the female population except accelerated growth and speech and language impairment[4].
There are also many X linked diseases which can be inherited from parents. If only the mother is affected by the disease (either genotypcially or phenotypically), a son is more likely to have the disease. This is because they only have one X chromosome so the affected gene will be expressed. A daughter will have a 50% chance of inheriting the disease. If only the father has the disease, 100% of daughters will be carriers as they inherit an X chromosome from each parent. A son will not inherit the disease as they inherit their X chromosomes maternally[5].
X chromosome Inactivation
X chromosome inactivation is the process by which all but one X chromosomes are defunctionalized in a cell and become barr bodies[6].
References
- ↑ Ross, MT et al. (2005). The DNA sequence of the human X chromosome. Nature, 434:325-337
- ↑ Who.int, (2014). WHO | Gender and Genetics. [online] Available at: http://www.who.int/genomics/gender/en/index1.html#KlinefelterSyndrome [Accessed 26 Nov. 2014].
- ↑ Who.int, (2014). WHO | Gender and Genetics. [online] Available at: http://www.who.int/genomics/gender/en/index1.html#Turnersyndrome [Accessed 26 Nov. 2014].
- ↑ Who.int, (2014). WHO | Gender and Genetics. [online] Available at: http://www.who.int/genomics/gender/en/index1.html#XXXFemales [Accessed 26 Nov. 2014].
- ↑ http://genome.wellcome.ac.uk/doc_WTD020851.html
- ↑ Ahn, J. and Lee, J. (2008) X chromosome: X inactivation. Nature Education, 1(1):24