Multiple allelism and pleiotropism must notes for bsc student for preparing University, Summaries of Botany and Agronomy

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has two contrasting forms, ie., alleles, g . . . roposed that each gene ; » But th (2) Multiple allelism : Mendel peng more than two alternative forms (allele). Presence of more than ti alle 0a fo o gahe is known as multiple allelism. Multiple alleles are soa on the same locy fonvologous EriDissomes Multiple alleles can be detected only in a population. Awell known example to explain multiple alleles in human beings is ABO blood type. Landsteiner discovered ABO system of blood groups. The fourth group AB was discovereg by de Castello and Steini. S of Bernstein showed that these groups are controlled by 3 alleles — 14, IP and I°/i, These alleles are autosomal and follow Mendelian pattern of inheritance. The alleles |* and I® produce a slightly different form of the sugar while I° doesn't Produce any sugar Because humans are diploid organism, each person possesses any two of the three | gene alleles, |A and I are completely dominant over I°, but when IA and I8 are present together they both express their own types of sugar thus, behaving as codominant alleles. Phenotype (Blood group) A B AB Genotype IIA or 1A | 18 (8 or 18 |o AB ° 1919 or ii Possible blood types of children from parents of various blood types. S.No. Blood groups Possibilities of of parents Children's blood group 1. AxA AandO 2 AxB A, B, AB and O 3. Ax AB A, B and AB 4. BxB Bando 5. AxO A and O 6. Bxo Bando 7 Bx AB A, B and AB 8, ABxO AandB 9. AB x AB A, B and AB . ) oO Other examples of multiple alleles are — Coat coil elf : ila and eo our in rabbit, eye colour in Drosophil Mineth 2 a where 'n' is number of alleles, = Scanned with CamSc