With suitable example, explain the concept of multiple allelism. (IFS 2022, 15 Marks)

Concept of Multiple Allelism

Multiple allelism refers to the existence of more than two alleles for a specific gene in a population. While an individual can only carry two alleles (one from each parent) for a gene, multiple alleles can exist in the gene pool of a population, leading to different genetic combinations.

• Key Features:
  
  • Multiple alleles exist for a single gene, but only two alleles are inherited by an individual.
  • This phenomenon occurs in the population level, meaning more than two alleles may be present in the gene pool.
  • The alleles can exhibit dominance, codominance, or incomplete dominance, depending on their interactions.

Example: ABO Blood Group System

• Genes and Alleles:
  
  • The ABO blood group system is determined by a single gene located on chromosome 9.
  • There are three alleles for this gene: IA, IB, and i.
    
    • IA: Codes for the A antigen.
    • IB: Codes for the B antigen.
    • i: Recessive allele, codes for no antigen.
• Phenotypic Expression:
  
  • IA and IB are both dominant to i.
  • IA and IB exhibit codominance, meaning both alleles can be expressed equally in individuals with both alleles (AB blood type).
• Blood Groups:
  
  • Blood Group A: Individuals with genotype IA IA or IA i.
  • Blood Group B: Individuals with genotype IB IB or IB i.
  • Blood Group AB: Individuals with genotype IA IB (codominant expression of both A and B antigens).
  • Blood Group O: Individuals with genotype ii (recessive).

Significance of Multiple Allelism

• Increased Genetic Variation: The presence of multiple alleles increases the genetic diversity within a population.
• Inheritance Pattern Complexity: Multiple allelism leads to more complex inheritance patterns compared to simple Mendelian inheritance.
• Genetic Studies: Understanding multiple allelism is crucial for genetic counseling, population genetics, and medical genetics, as seen in blood transfusion compatibility.

Conclusion

Multiple allelism is a fascinating genetic concept that highlights the diversity and complexity of genetic traits within populations. By studying examples like the ABO blood group system, we can better understand how multiple alleles contribute to the variation in phenotypic traits and the inheritance patterns observed in organisms.