This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
True about polymorphism is: (PGI Dec 2006) 
Select and explain. 
A. Single locus - multiple normal alleles, B. Single locus - multiple abnormal alleles, C. Single phenotype: single Iocus->multiple normal alleles multiple abnormal alleles, D. Single phenotype: Single !ocus->>multiple abnormal alleles.
D: Single phenotype: Single !ocus->>multiple abnormal alleles.
Answer: D: Single phenotype: Single !ocus->>multiple abnormal alleles. 
Explanation: Ans: D (Single phenotype, single locus, - multiple allele] Polymorphisms is single phenotype, single locus & mu Itipie normal allele(r)Polymorphisms# Clinically ,'iarmless variationQ of DNA sequence# Normal variation in DNA sequence that have frequency of at least 1%. Usally, they don't result in a perceptible phenotype i.e,phenotype same'Q.They constitutes: Single base-pair substitution (often) & Deletions and insertionsThey don't alter protein coding sequence probaly due to degeneracy of genetic code although it is possible that it might alter mRNA stability, translation or aminoacid sequences.