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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.
In Mendelian inheritance, genes have only two alleles, such as a and A. Mendel consciously chose pairs of genetic traits, represented by two alleles for his inheritance experiments. In nature, such genes often exist in several different forms and are therefore said to have multiple alleles. An individual usually has only two copies of each gene ...
One example is the gene CD14, which is known to have a polymorphism that is associated with increased amounts of CD14 protein as well as reduced levels of IgE serum. [30] A study was conducted on 624 children looking at their IgE serum levels as it related to the polymorphism in CD14.
In medical genetics, compound heterozygosity is the condition of having two or more heterogeneous recessive alleles at a particular locus that can cause genetic disease in a heterozygous state; that is, an organism is a compound heterozygote when it has two recessive alleles for the same gene, but with those two alleles being different from each other (for example, both alleles might be ...
An example of a botanical genetic polymorphism is heterostyly, in which flowers occur in different forms with different arrangements of the pistils and the stamens. The system is called heteromorphic self-incompatibility , and the general 'strategy' of stamens separated from pistils is known as herkogamy .
Suppose two subsequent speciation events occur where an ancestor species gives rise firstly to species A, and secondly to species B and C. When studying a single gene, it can have multiple versions causing different characters to appear (polymorphisms). In the example shown in Figure 1, the gene G has two versions (alleles), G0 and G1.
Pseudoallelism is a state in which two genes with similar functions are located so close to one another on a chromosome that they are genetically linked. [1] [2] This means that the two genes (pseudoalleles) are nearly always inherited together.
For example, Clarence Little and William E. Castle did credit Cuénot with the discovery of the first lethal mutation. [5] The mouse geneticist Clarence Little credited Cuénot with the idea and first evidence for multiple allelism, and recognizing that the inheritance of white spotting in the mouse did not breed true. [6] [7]