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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.
Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total number of protein-coding genes in a complete haploid set of 23 chromosomes is estimated at 19,000–20,000. [2] Genes may possess multiple variants known as alleles, and an allele may also be said to reside at a particular locus.
A cell is said to be homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes. [ 2 ] An individual that is homozygous-dominant for a particular trait carries two copies of the allele that codes for the dominant trait .
Under the Polygenic Model, for traits, like height, to be continuous in a population there must be many genes that code for the trait. Otherwise, the expression of the trait is limited by the number of possible combinations of alleles. The many genes which code for the continuous trait are also further modified by environmental conditions. [3]
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. [4] Contrast allozygote. auxesis The growth of a multicellular organism due to an increase in the size of its cells rather than an increase in the number of cells. axenic
Interpreting Serotypes as Alleles: HL-A1 antiserum reacts to HLA-A1 gene product, a cell surface antigen, the similar cell surface antigens are found on almost all cells in the body. The frequency of HLA-A1 alleles is: HLA-A1*0101- 17.3%, *0103- 0.016%. The frequency of *0101 is 1000 times more abundant than *0103, or 99.9% of the time you have ...
Each STR is polymorphic, but the number of alleles is very small. Typically each STR allele will be shared by around 5 - 20% of individuals. The power of STR analysis comes from looking at multiple STR loci simultaneously. [6] The pattern of alleles can identify an individual quite accurately. Thus STR analysis provides an excellent ...
A multilocus genotype is the combination of alleles found at two or more loci in a single individual. For example, in a diploid species, if there are two SNP loci and the first locus has alleles A and G, while the second locus has alleles T and C, the multilocus genotype can be represented as {A/G,T/C}. If the genome is not haploid then the ...