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Multiple Alleles - Examples Of Multiple Alleles, Polymorphism In Noncoding Dna, Making Use Of Polymorphic Dna

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Alleles are alternative forms of a gene, and they are responsible for differences in phenotypic expression of a given trait (e.g., brown eyes versus green eyes). A gene for which at least two alleles exist is said to be polymorphic. Instances in which a particular gene may exist in three or more allelic forms are known as multiple allele conditions. It is important to note that while multiple alleles occur and are maintained within a population, any individual possesses only two such alleles (at equivalent loci on homologous chromosomes).

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Multiple Alleles - Examples Of Multiple Alleles

Two human examples of multiple-allele genes are the gene of the ABO blood group system, and the human-leukocyte-associated antigen (HLA) genes. The ABO system in humans is controlled by three alleles, usually referred to as IA, IB, and IO (the "I" stands for isohaemagglutinin). IA and IB are codominant and produce type A and type B antigens, respectively, which migrate to the surface…

Multiple Alleles - Polymorphism In Noncoding Dna

It must be realized that although the above two are valid examples, most genes are not multiply allelic but exist only in one or two forms within a population. Most of the DNA sequence variation between individuals arises not because of differences in the genes, but because of differences in the noncoding DNA found between genes. An example of a noncoding DNA sequence that is extremely abundant in…

Multiple Alleles - Making Use Of Polymorphic Dna

Multiple alleles and noncoding polymorphic DNA are of considerable importance in gene mapping—identifying the relative positions of genetic loci on chromosomes. Gene maps are constructed by using the frequency of crossing-over to estimate the distance between a pair of loci. To obtain a good estimate, one must analyze a large number of offspring from a single cross. In laboratory organisms …

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about 1 month ago

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