Mendelian laws were the central part of the genetics that contributed significantly in shaping the hereditary patterns of genes. However, some limitations were found due times. After rediscovery of Mendel’s law of inheritance, various geneticist conducted experiments & obtain results which were different from Mendel’s laws. One such exception is applied in the case of multiple allelism. Where any character is controlled by more than two alternating forms of genes, alleles. It is now well established that all characters of as individual is not controlled by two alternative forms of genes or alleles, rather through several alternative forms or alleles. When any of the three or more allele forms of a gene occupy the same locus in a given pair of homologous chromosomes, they are said to constitute a series of multiple alleles. Multiple alleles exhibit distinguished features like: i) Multiple allele always occupy same locus is the chromosome. ii) Always
Polygenic inheritance: When a trait is controlled by more than one pair of contrasting gene ( generally a pair of allele) and follows non Mendelian inheritance pattern it is called polygenic trait and the pattern of Inheritance called Polygenic Inheritance. It refers to Inheritance of quantitative traits which are influenced by multiple genes to different loci and environment may also be involved. A quantitative trait is a measurable phenotype that depends on the cumulative actions of many genes and the environment. These traits can vary among individuals, over a range, to produce a continuous distribution of phenotypes. Examples include height, weight and blood pressure. It is charact erized by Ø Involvement of several loci in the expression of the trait. Ø There is no dominant and recessive relationship at each of the loci. Ø The loci at in an addition fashion, in adding and detracting a small amount from the phenotype. Ø The environment interacts with the genot