Pseudoalleles

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Pseudoalleles

Pseudoalleles
In previous section of multiple allelism, we have observed that multiple alleles occupied same gene locus in both homologous chromosomes and never undergo crossing over, but there is one possibility that certain gene loci may be so closely linked to each other that they may inherit together and may have minimum chances of crossing over. Then, such genes which are actually different type of genes, may behave like alleles of same gene and erroneously may be considered as multiple alleles. Such genes which have two separate gene loci, but often inherit together due to close linkage and have very rare chance of crossing over are called pseudoalleles (Lewis, 1951). There is a Jot of controversy about the exact definition of pseudoalleles.

According to Lewis (1955) and Green (1963), the pseudo alleles may be regarded as distinct genes with their own particular functions which must be carried out in sequence at the same intracellular location. Pontecorvo( 1958) considered pseudoalleles as different mutational and recombinational sites within the same gene-that is, the gene must be regarded as subdivisible and defined by functional properties. The gene then functions only when all its subunits occur in one sequential group; its function is interfered with by change (mutation) at any one of several internal points.

Recombination, by crossing over, may also occur within such a gene rather than only between the genes. Such a functional gene, as defined by the cis-trans test, has been termed cistron (Benzer, 1957). The concept of pseudoallelism has two fold significance : (i) It shows the possibility of division of classical gene into a structural and a functional unit and (ii) it provides a clue for intergenic units of recombination and mutation.

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