Question

List three allelic form of gene I in human . Explain the different phenotypic expression, control by these three forms .​

Answer 1

Explanation:

The human cytochrome P450 3A4 (CYP3A4) plays a dominant role in the metabolism of numerous clinically useful drugs. Alterations in the activity or expression of this enzyme may account for a major part of the variation in drug responsiveness and toxicity. However, it is generally accepted that most of the known single nucleotide polymorphisms in the coding and 5'-flanking regions are not the main determinants for the large inter-individual variability of CYP3A4 expression and activity. We show that the allelic variation is critically involved in determining the individual total hepatic CYP3A4 mRNA level and metabolic capability. There exists a definite correlation between the total CYP3A4 mRNA level and allelic expression ratio, the relative transcript level ratio derived from the two alleles. Individuals with a low expression ratio, exhibiting a large difference of transcript level between the two alleles, revealed extremely low levels of total hepatic CYP3A4 mRNA, and thus low metabolic capability as assessed by testosterone 6beta-hydroxylation. These results present a new insight into the individualized CYP3A4-dependent pharmacotherapy and the importance of expression imbalance to human phenotypic diversity.

Answer 2

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The three different forms of gene I are IA, IB and i., ABO blood grouping is controlled by these three alleles, hence it is an example of multiple allelism. Each person possesses any two of the three I gene alleles. lA and lB are completely dominant over allele (l) while IA and IB are co-dominant because both of them express themselves equally and independently when present together. As there are three alleles of gene I there would be following six types of allelic combinations of genotypes resulting in four phenotypic expressions as follows : Read more on Sarthaks.com - https://www.sarthaks.com/185800/different-allelic-humans-explain-different-phenotypic-expressions-controlled-these-three.

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