Practice Questions

TLS Online TPP Program

#Question id: 15654

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. Next you isolate a mutation, designated MelB–, which gives uninducible melibiase activity. Mapping experiments show that MelB– is linked to Mel1. Using an F' factor that carries the chromosomal region surrounding Mel1, you perform the following genetic tests:

Describe the basic genetic properties of the MelB– mutation?

#SCPH01 Biochemistry

MelB- is a dominant mutation whose wild-type allele codes for a trans-acting factor that is not Mel1
MelB- is a recessive mutation whose wild-type allele codes for a cis-acting factor that is not Mel1
MelB- is a dominant-recessive mutation whose wild-type allele codes for a cis-acting factor that is not Mel1
MelB- is a recessive mutation whose wild-type allele codes for a trans-acting factor that is not Mel1