Hereditary carrier: Difference between revisions
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{{Short description|Organism with a recessive genetic allele that does not display the recessive trait}} |
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{{unreferenced|date=May 2010}} |
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[[File:Autosomal recessive inheritance - Carriers.png|thumb|[[Punnett square]]: If the other parent does not have the recessive genetic disposition, it does not appear in the [[phenotype]] of the children, but on the average 50% of them become carriers.]] |
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A ''' |
A '''hereditary carrier''' ('''genetic carrier''' or just '''carrier'''), is a person or other organism that has [[Genetics|inherited]] a recessive allele for a genetic trait or mutation but usually does not display that [[genetic trait|trait]] or show symptoms of the [[Genetic disease|disease]]. Carriers are, however, able to [[Heredity|pass]] the [[allele]] onto their offspring, who may then express the genetic trait. |
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== Carriers in autosomal inheritances == |
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[[File:Autosomal recessive inheritance - segregation.png|thumb|Punnett square: If both parents are carriers, on the average 25 % of the offspring have the recessive trait in phenotype and 50 % are carriers.]] |
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[[Autosomal]] dominant-recessive [[inheritance (biology)#obligatory data|inheritance]] is made possible by the fact that the individuals of most species (including all higher animals and plants) have two [[alleles]] of most hereditary predispositions because the [[chromosomes]] in the [[cell nucleus]] are usually present in pairs ([[diploid]]). Carriers can be female or male as the autosomes are homologous independently from the sex. |
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In carriers the expression of a certain characteristic is recessive. The individual has both a genetic predisposition for the [[dominance (genetics)|dominant]] trait and a genetic predisposition for the recessive trait, and the dominant expression prevails in the [[phenotype]]. In an individual which is [[heterozygous]] regarding a certain allele, it is not externally recognisable that it also has the recessive allele. But if the carrier has a child, the recessive trait appears in the phenotype, in case the descendant receives the recessive [[allele]] from both parents and therefore does not possess the dominant allele that would cover the recessive trait. According to [[Mendelian inheritance|Mendelian Law of Segregation of genes]] an average of 25% of the offspring become [[homozygous]] and express the recessive trait. Carriers can either pass on normal autosomal recessive hereditary traits or an autosomal recessive [[hereditary disease]]. |
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Up to 1 in 25 individuals of Northern European ancestry may be considered carriers of mutations that could lead to [[Cystic Fibrosis]]. The disease appears only when two of these carriers have children, as each pregnancy between them will have a 25% chance of producing a child with the disease. However, it is also thought that carriers may be more resistant to diarrhea during [[typhoid fever]] or [[cholera]], and are therefore not truly asymptomatic. This resistance leads to [[Heterozygote advantage|increased survival]] of the carriers, thereby increasing the frequency of the altered [[Cystic fibrosis transmembrane conductance regulator|genes]] in the population. |
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== Carriers in gonosomal inheritances == |
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Genetic carrier testing can be used to tell if a person carries one or more mutations of the CF gene and how many copies of each mutation. The test looks at a person’s DNA (genetic material), which is taken from cells in a blood sample or from cells that are gently scraped from inside the mouth. |
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[[File:Gonosomal recessive inheritance.png|thumb|The mother is a carrier of the recessive hereditary disposition for [[Color blindness]]. The Y chromosome of the father cannot oppose this. The healthy allele on the X chromosome of the father can compensate for this in a daughter. She can see normally, but she becomes a conductor. The same pattern of inheritance applies to [[Haemophilia]].]] |
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[[Gonosome|Gonosomal]] recessive genes are also passed on by carriers. The term is used in [[human genetics]] in cases of hereditary traits in which the observed trait lies on the female [[gonosome|sex chromosome]], the [[X chromosome]]. These are [[Sex linkage|sex-linked]] genes. The carriers are always [[Woman|women]]. Women have two homologous sex chromosomes (XX). [[Man|Men]] cannot be carriers because they only have one X chromosome. If a man has a certain recessive genetic disposition on his X chromosome, this is called ''hemizygous'' and it gets phenotypically expressed. |
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Although the Y chromosome is not a really homologous chromosome and carries relatively little genetic information compared to X chromosomes, a genetic component on the Y chromosome can come to expression because there is no homologous chromosome with an allele which could overlay it. |
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Although only about one of every 3,000 Caucasian newborns has CF, there are more than 1,000 known mutations of the gene that causes CF. Current tests look for the most common mutations. |
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Examples of traits inherited via the X chromosome are [[color blindness]] and the most common hereditary form of [[haemophilia]] which therefore affect men much more often than women.<ref>[[Neil A. Campbell]], [[Jane B. Reece]]: ''Biologie.'' Spektrum-Verlag 2003, {{ISBN|3-8274-1352-4}}, page 308–311.</ref><ref>Ulrich Weber: ''Biologie Gesamtband Oberstufe,'' Cornelsen-Verlag 2001, {{ISBN|3-464-04279-0}}, page 178–182.</ref> |
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The mutations screened by the test vary according to a person's race or ethnic group, or by the occurrence of CF already in the family. More than 10 million Americans, including one in 29 Caucasian Americans, are carriers of one mutation of the CF gene. In other races or ethnicities, one in 46 Hispanic Americans, one in 65 African Americans and one in 90 Asian Americans carry a mutation of the CF gene. |
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[[File:Erbgang Bluterkrankheit.svg|thumb|left|Inheritance by female carriers]] |
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| ⚫ | [[Queen Victoria]], and her daughters Princesses Alice and Beatrix, were carriers of the [[hemophilia]] gene (an abnormal allele of a gene, necessary to produce one of the blood clotting factors). Both had children who continued to pass on the gene to succeeding generations of the royal houses of [[Spain]] and [[Russia]], into which they married.<ref>Potts, W.T.W. "Royal Haemophilia." Journal of Biological Education (Society of Biology) 30.3 (1996): 207. Academic Search Premier. 16 Sept. 2013</ref> Since males only have one X chromosome, males who carried the altered gene had hemophilia B. Those female children who inherited the altered gene were asymptomatic carriers who also would have passed it to half of their children. |
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Gonosomal dominant inheritances are also known. There are ''no'' carriers since owners of a dominant hereditary disposition phenotypically express the trait in each case. |
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If you have a relative with CF or who is known to carry a mutation of the CF gene, your chances of carrying a mutation are greater because of your family's history. If you are pregnant or planning to have a child, you should discuss this test and the results with a health professional who is knowledgeable about genetic testing, such as a genetic counselor. |
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==References== |
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{{reflist}} |
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[[Category:Genetics]] |
[[Category:Genetics]] |
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{{genetics-stub}} |
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[[ht:Pòtè]] |
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[[no:Bærer (genetikk)]] |
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[[fi:Kantaja (biologia)]] |
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Latest revision as of 01:08, 21 August 2024
A hereditary carrier (genetic carrier or just carrier), is a person or other organism that has inherited a recessive allele for a genetic trait or mutation but usually does not display that trait or show symptoms of the disease. Carriers are, however, able to pass the allele onto their offspring, who may then express the genetic trait.
Carriers in autosomal inheritances
[edit]
Autosomal dominant-recessive inheritance is made possible by the fact that the individuals of most species (including all higher animals and plants) have two alleles of most hereditary predispositions because the chromosomes in the cell nucleus are usually present in pairs (diploid). Carriers can be female or male as the autosomes are homologous independently from the sex.
In carriers the expression of a certain characteristic is recessive. The individual has both a genetic predisposition for the dominant trait and a genetic predisposition for the recessive trait, and the dominant expression prevails in the phenotype. In an individual which is heterozygous regarding a certain allele, it is not externally recognisable that it also has the recessive allele. But if the carrier has a child, the recessive trait appears in the phenotype, in case the descendant receives the recessive allele from both parents and therefore does not possess the dominant allele that would cover the recessive trait. According to Mendelian Law of Segregation of genes an average of 25% of the offspring become homozygous and express the recessive trait. Carriers can either pass on normal autosomal recessive hereditary traits or an autosomal recessive hereditary disease.
Carriers in gonosomal inheritances
[edit]
Gonosomal recessive genes are also passed on by carriers. The term is used in human genetics in cases of hereditary traits in which the observed trait lies on the female sex chromosome, the X chromosome. These are sex-linked genes. The carriers are always women. Women have two homologous sex chromosomes (XX). Men cannot be carriers because they only have one X chromosome. If a man has a certain recessive genetic disposition on his X chromosome, this is called hemizygous and it gets phenotypically expressed.
Although the Y chromosome is not a really homologous chromosome and carries relatively little genetic information compared to X chromosomes, a genetic component on the Y chromosome can come to expression because there is no homologous chromosome with an allele which could overlay it.
Examples of traits inherited via the X chromosome are color blindness and the most common hereditary form of haemophilia which therefore affect men much more often than women.[1][2]
Queen Victoria, and her daughters Princesses Alice and Beatrix, were carriers of the hemophilia gene (an abnormal allele of a gene, necessary to produce one of the blood clotting factors). Both had children who continued to pass on the gene to succeeding generations of the royal houses of Spain and Russia, into which they married.[3] Since males only have one X chromosome, males who carried the altered gene had hemophilia B. Those female children who inherited the altered gene were asymptomatic carriers who also would have passed it to half of their children.
Gonosomal dominant inheritances are also known. There are no carriers since owners of a dominant hereditary disposition phenotypically express the trait in each case.
References
[edit]- ^ Neil A. Campbell, Jane B. Reece: Biologie. Spektrum-Verlag 2003, ISBN 3-8274-1352-4, page 308–311.
- ^ Ulrich Weber: Biologie Gesamtband Oberstufe, Cornelsen-Verlag 2001, ISBN 3-464-04279-0, page 178–182.
- ^ Potts, W.T.W. "Royal Haemophilia." Journal of Biological Education (Society of Biology) 30.3 (1996): 207. Academic Search Premier. 16 Sept. 2013