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An allele [1] (or allelomorph) is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule. [2]Alleles can differ at a single position through single nucleotide polymorphisms (SNP), [3] but they can also have insertions and deletions of up to several thousand base pairs.
Thus, allele R is dominant over allele r, and allele r is recessive to allele R. [4] Dominance is not inherent to an allele or its traits . It is a strictly relative effect between two alleles of a given gene of any function; one allele can be dominant over a second allele of the same gene, recessive to a third, and co-dominant with a fourth.
Genes may possess multiple variants known as alleles, and an allele may also be said to reside at a particular locus. Diploid and polyploid cells whose chromosomes have the same allele at a given locus are called homozygous with respect to that locus, while those that have different alleles at a given locus are called heterozygous. [3]
In the example on the right, both parents are heterozygous, with a genotype of Bb. The offspring can inherit a dominant allele from each parent, making them homozygous with a genotype of BB. The offspring can inherit a dominant allele from one parent and a recessive allele from the other parent, making them heterozygous with a genotype of Bb.
A relationship between the alleles of a gene in which one allele produces an effect on phenotype that overpowers or "masks" the contribution of another allele at the same locus; the first allele and its associated phenotypic trait are said to be dominant, and the second allele and its associated trait are said to be recessive. Often, the ...
In this case, someone who expresses an X-linked dominant allele will exhibit the disorder and be considered affected. [citation needed] The pattern of inheritance is sometimes called criss-cross inheritance. [1] X-linked dominant traits do not necessarily affect males more than females (unlike X-linked recessive traits). The exact pattern of ...
The O allele lacks both enzymatic activities because of the frameshift caused by a deletion of guanine-258 in the gene which corresponds to a region near the N-terminus of the protein. [10] This results in a frameshift and thus of a truncated protein of only 117 amino acids .
The advantageous extreme allele will increase in frequency among the population as a consequence of survival and reproduction differences among the different present phenotypes in the population. The allele fluctuations as a result of directional selection can be independent of the dominance of the allele, and in some cases if the allele is ...