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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.
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 ]
Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion. [1] Gene conversion can be either allelic, meaning that one allele of the same gene replaces another allele, or ectopic, meaning that one paralogous DNA sequence converts another.
Allelic exclusion is a process by which only one allele of a gene is expressed while the other allele is silenced. [1] This phenomenon is most notable for playing a role in the development of B lymphocytes, where allelic exclusion allows for each mature B lymphocyte to express only one type of immunoglobulin.
Read-out is one, two or zero fluorescent dots, which indicates mono-,di-allelic or no expression respectfully at single cell resolution. Cell sorting if the gene is a surface protein, and there is the allele-specific antibody , this technique can be used to detect presence or absence of fixed or dynamic RME by running the same cell over the time.
A cell or organism that is homozygous for a locus at which the two homologous alleles are identical by descent, both having been derived from a single gene in a common ancestor. [8] Contrast allozygote .
The allele frequency spectrum can be written as the vector = (,,,,), where is the number of observed sites with derived allele frequency .In this example, the observed allele frequency spectrum is (,,,,), due to four instances of a single observed derived allele at a particular SNP loci, two instances of two derived alleles, and so on.
A genetic lineage includes all descendants of a given genetic sequence, typically following a new mutation.It is not the same as an allele because it excludes cases where different mutations give rise to the same allele, and includes descendants that differ from the ancestor by one or more mutations.