Multiple allele, Pseudo-allele and Pleiotropy

 Several cases of multiple alleles and pseudo alleles are known both in animals and plants. Some well-known cases of multiple alleles include (1) Fur color in rabbits (2) Wing type in Drosophila (3) Eye color in Drosophila (4) Self-incompatibility alleles in plants (5) ABO blood group in man, etc. Now it is believed that most of the genes have multiple alleles if in-depth investigations are made. Fur Colour in rabbits The fur color in rabbits is a well-known example of multiple alleles. In rabbits, the fur color is of four types viz., agouti, chinchilla, Himalayan, and albino. i. Agouti- This has full color and is also known as wild type. This color is dominant over all the remaining colors and produces agouti color in F1 and 3:1 ratio in F2 when crossed with any of the other three colors in rabbits. This color is represented by C. ii. Chinchilla- This is lighter than agouti. This color is dominant over Himalayan and albino and produces chinchilla in F1 and 3:1 ratio in F2 when cro...

 Mendel implied that only two alleles, one dominant and one recessive, could exist for a given gene. Alleles are alternative forms of a gene, and they are responsible for differences in the phenotypic expression of a given trait (e.g., brown eyes versus green eyes). Although individual humans (and all diploid organisms) can only have two alleles for a given gene, multiple alleles may exist at the population level such that many combinations of two alleles are observed. Note that when many alleles exist for the same gene, the convention is to denote the most common phenotype or genotype among wild animals as the wild type (often abbreviated “+”); this is considered the standard or norm. All other phenotypes or genotypes are considered variants of this standard, meaning that they deviate from the wild type. The variant may be recessive or dominant to the wild-type allele. Thus, more than two kinds of alleles occupying the same locus in the individual chromosomes are referred to as mu...