Question

Assume that humans have the following (hypothetical) metabolic pathway: 1 Enta 2 в B 3 ic ID You can assume that having one functional copy of gene A, B, C, or D results in a wild-type phenotype Q1. Mary is homozygous for a mutation in gene A, which results in a non- functional enzyme A. What will the result be? List each compound that will be affected and how its level might change. What changes could theoretically cause an abnormal phenotype (symptoms)? Q2. Tim is homozygous for a mutation in gene B resulting in the absence of enzyme B. What will the result be? List each compound that will be affected and how its level might change. Q3. If Mary and Tim have children, what are the possible genotypes and phenotypes of their children? Note: Assume that Mary and Tim are homozygous for the wild-type alleles for all genes other than A and B, respectively. Now what I would like you

Answer 1

Ans 1: As we can see from the hypothetical pathway each enzyme is unique for the pathway and functional unavailability of any single enzyme causes the metabolice pathway to be shut down. Now Mary does not have a functional enzyme A so this means that this pathway will not be completed because enzyme A is unique to this pathway and its absence does not fulfilled by any other enzyme. Compound 2,3 and 5 level will be decreased because of the absence of the enzyme A as we can see in the pathway that A is required for the conversion of 1 to 2 and 2 will further converted to 3 and 5 through different enzyme but because of the non availability of enzyme A 1 will not be converted to 2 and 2 level decreases and so will the level of 3 and 5. Now 1 has only a single choice to convert into 4 as enzyme C is still functional. So there will be increase in the level of 1 and 4 as 1 can undergo only single reaction apart from normal pathway.

Ans 2: Now Tim does not contain functional B enzyme, this will also leads to the incompletion of the metabolic pathway as this enzyme is also unique to this pathway and its absence can't be fulfilled. Level of compound 3 will decrease as the enzyme B is absent compound 2 will not be converted to compound 3 and compound 4 and compound 2 level will increase because all the part of compound 2 which will be convertible will convert to compound 4 by functional enzyme D and remaining pathway is not affected by the absence of enzyme B so compound 1 will still converted to compound 2 but compound 2 will converted to compound 4 only instead to compound 3 and 4. So there will be a rise in the level of compound 2 also.

Ans 3: Now as described in the question having one functional copy of gene A,B,C,D results in wild type phenotype which means that the genes are dominanting in nature. As described in the question Tim and Mary both are homozygous for a mutation in Gene B and Gene A respectively which means that they do not possess a single functional gene B and A respectively. So their children also do not possess the functional copy of gene A and B but they do possess functional copy of other genes C and D becuase Tim and Mary also possess them. So the phenotype of their children will be no funtional A and B enzyme but have functional C and D enzyme.