You are studying a new strain of E. coli that can utilize the disaccharide melibiose very efficiently. You find that utilization depends on the enzyme melibiase, which is encoded by the gene Mel1. Mel1 is not expressed unless melibiose is present in the growth medium. You have isolated a mutation that causes constitutive melibiase activity, which you designate MelA–. P1 phage mapping experiments using a Tn5 insertion linked to Mel1 show that MelA– is not linked to Mel1. Moreover you find that when an amber suppressor is introduced into a MelA– mutant, normal melibiase regulation is restored. Classify the MelA– mutation on the basis of genetic properties,  make a proposal for the type of regulatory functions affected by the MelA– mutation?

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#Question id: 11571

#Unit 7. System Physiology – Animal

Which of the following is the most likely explanation for hypothyroidism in a patient whose iodine level is normal?

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#Question id: 32360

#Unit 1. Molecules and their Interaction Relevant to Biology

2-Deoxyglucose (2-DG) inhibits the proliferation of cells and hence finds use as an anti-cancer agent, inhibiting the activities of which of the following enzymes?

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#Question id: 12493

#Unit 8. Inheritance Biology

Cystic fibrosis shows autosomal recessive inheritance with an incidence of 1 in 2500. The unaffected brother of an affected girl is referred for genetic counseling. Assume that the population is in Hardy-Weinberg equilibrium. Which of the following is correct?

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#Question id: 2799

#Unit 2. Cellular Organization

There are five major types of histones in eukaryotic cells. One of these is not part of the structure of nucleosomes and is thought to participate in forming the 30-nm condensed chromatin fiber. Which histone is this?

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#Question id: 10843

#Unit 10. Ecological Principles

For a Batesian mimicry system to work,