Hereditary carrier: Difference between revisions
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== Carriers in autosomal inheritances == |
== 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.]] |
[[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|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|cell nucleus]] are usually present in pairs ([[diploid]]). In carriers the expression of a certain [[characteristic#biology|characteristic]] is [[recessive]] (from Latin recedere). The individual has both a genetic predisposition for the [[dominance (genetics)|dominant]] |
[[autosomal|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|cell nucleus]] are usually present in pairs ([[diploid]]). In carriers the expression of a certain [[characteristic#biology|characteristic]] is [[recessive]] (from Latin ''recedere'' "withdraw"). 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 recognizable that it also has the recessive allele. But if a carrier has offspring, the recessive trait appeares in the phenotye, in case the descendant receives the recessive [[allele]] from both parents and therefore does not have 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 recessive hereditary traits or a recessive [[hereditary disease]]. |
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==X-linked genes== |
==X-linked genes== |
Revision as of 17:14, 23 September 2019
This article needs additional citations for verification. (October 2013) |
![](/upwiki/wikipedia/commons/thumb/0/07/Autosomal_recessive_inheritance_-_Carriers.png/220px-Autosomal_recessive_inheritance_-_Carriers.png)
A hereditary 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.
Carriers in autosomal inheritances
![](/upwiki/wikipedia/commons/thumb/7/79/Autosomal_recessive_inheritance_-_segregation.png/220px-Autosomal_recessive_inheritance_-_segregation.png)
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). In carriers the expression of a certain characteristic is recessive (from Latin recedere "withdraw"). 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 recognizable that it also has the recessive allele. But if a carrier has offspring, the recessive trait appeares in the phenotye, in case the descendant receives the recessive allele from both parents and therefore does not have 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 recessive hereditary traits or a recessive hereditary disease.
X-linked genes
Queen Victoria, and her daughters Princesses Alice and Beatrix, were carriers of the X-linked 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.[1] Since males only have one X chromosome, males who carried the altered gene had hemophilia B. Females have two X chromosomes, so one copy of an X-linked recessive gene would cause them to be an asymptomatic carrier. These females simply passed it to half of their children.[2]
Cystic fibrosis
Up to 1 in 25 individuals of Northern European ancestry may be considered carriers of mutations (CFTR genes) that can 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. Although only about 1 of every 3,000 Caucasian newborns has CF, there are more than 900 known mutations of the gene that causes CF. Current tests look for the most common mutations.[3]
Genetic 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, which is taken from cells in a blood sample or from cells that are gently scraped from inside the mouth.
The mutations screened by the test vary according to a person's ethnic group or by the occurrence of CF already in the family. More than 10 million Americans, including 1 in 25 Caucasian Americans, are carriers of one mutation of the CF gene. CF is present in other races, though not as frequently as in Caucasian individuals. 1 in 46 Hispanic Americans, 1 in 65 African Americans, and 1 in 90 Asian Americans carry a mutation of the CF gene.[3]
Sickle cell anemia
Sickle cell anemia is the most common genetic disorder among African Americans in the United States. While approximately 8% are carriers, 1 in 375 African Americans are born with the disease. Carriers are typically asymptomatic, but they may show symptoms at high altitudes or under oxygen-poor environments as in instances of extreme exercise.[3] Carriers are also known to be resistant to malaria, suggesting there is a heterozygote advantage in certain regions of Africa. This is a probable explanation for why the disease is most prevalent among African Americans [4]
See also
Conductor of recessive gene (genetics)
References
- ^ Potts, W.T.W. "Royal Haemophilia." Journal of Biological Education (Society of Biology) 30.3 (1996): 207. Academic Search Premier. 16 Sept. 2013
- ^ Pagon, R. A.; Adam, M. P.; Ardinger, H. H. "Illustrated Glossary". GeneReviews. University of Washington, Seattle. Retrieved 15 December 2014.
- ^ a b c Edwards, Q. T.; Seibert, D.; Macri, C.; Carolyn, C.; Tilghman, J. (November 2004). "Assessing ethnicity in preconception counseling: Genetics--what nurse practitioners need to know". Clinical Practice. 16 (11): 472–480. doi:10.1111/j.1745-7599.2004.tb00426.x.
- ^ B., G. (October 5, 1956). "Malaria and Sickle-Cell Anemia". Science. 124: 619–624. doi:10.1126/science.124.3223.619.