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Question
Which of the following inheritance is controlled by multiple alleles?
Which of the following inheritance is controlled by multiple alleles?
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Solution
The correct option is B Blood groups
Colour blindness gene is present on X-chromosome; the mutated allele is shown by Xc which causes absence of pigments in cones resulting in inability to differentiate colours. The presence of wild type allele marks the presence of pigments in cones. Sickle cell anemia is inherited from parents to offspring and hence is a genetic trait. The governing gene (Hbb) is present on chromosome 11. Missense mutation, single base mutation of A by T at the 17th nucleotide of the Hbb gene changes the codon GAG (glutamic acid) to GTG (which encodes valine). The mutated allele Hbs encodes the abnormal haemoglobin molecules which stick to one another and cause stiffness and sickle shape of red blood cells. Both copies of the gene in each cell must have mutations to express the symptoms.
Phenylketonuria is caused by mutation in PAH gene, present on chromosome 12, responsible for an enzyme called phenylalanine hydroxylase, which breaks down phenylalanine into tyrosine not into alanine. The wild type allele codes for functional enzyme while the mutated allele codes defective enzyme or no enzyme.
Human blood group inheritance is governed by three alleles namely IA, IB and IO of gene "I". IA and IB show codominance while allele "IO" is recessive to both "IA" and "IB". This gives total six genotypes and four phenotypes - A (IA IA and IA IO), B (IB IB and IB IO), AB (IA IB) and O (IOIO). Thus, all mentioned traits except blood group are governed by two allele of a gene while blood group is governed by three allele of a gene and hence is an example of multiple allelism. Correct option is "C".
Colour blindness gene is present on X-chromosome; the mutated allele is shown by Xc which causes absence of pigments in cones resulting in inability to differentiate colours. The presence of wild type allele marks the presence of pigments in cones. Sickle cell anemia is inherited from parents to offspring and hence is a genetic trait. The governing gene (Hbb) is present on chromosome 11. Missense mutation, single base mutation of A by T at the 17th nucleotide of the Hbb gene changes the codon GAG (glutamic acid) to GTG (which encodes valine). The mutated allele Hbs encodes the abnormal haemoglobin molecules which stick to one another and cause stiffness and sickle shape of red blood cells. Both copies of the gene in each cell must have mutations to express the symptoms.
Phenylketonuria is caused by mutation in PAH gene, present on chromosome 12, responsible for an enzyme called phenylalanine hydroxylase, which breaks down phenylalanine into tyrosine not into alanine. The wild type allele codes for functional enzyme while the mutated allele codes defective enzyme or no enzyme.
Human blood group inheritance is governed by three alleles namely IA, IB and IO of gene "I". IA and IB show codominance while allele "IO" is recessive to both "IA" and "IB". This gives total six genotypes and four phenotypes - A (IA IA and IA IO), B (IB IB and IB IO), AB (IA IB) and O (IOIO). Thus, all mentioned traits except blood group are governed by two allele of a gene while blood group is governed by three allele of a gene and hence is an example of multiple allelism. Correct option is "C".
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