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?

TLS Online TPP Program

#Question id: 33478

#Unit 2. Cellular Organization

Find true and false statements

A. Comparisons of related genes in different species show that the sequences of the corresponding exons are usually conserved

B. when two genes are related, the relationship between their exons is closer than the relationship between their introns.

C. The sequences of the introns are much less similar.

D. Introns evolve much more rapidly than exons because of the lack of selective pressure to produce a polypeptide with a useful sequence.

TLS Online TPP Program

#Question id: 33479

#Unit 2. Cellular Organization

TLS Online TPP Program

#Question id: 33480

#Unit 2. Cellular Organization

Finding: The overall degree of divergence between two homologous exons in related genes corresponds to the differences between the polypeptides.

Reason: Overall degree of divergence between two homologous exons is mostly a result of base substitutions.

TLS Online TPP Program

#Question id: 33481

#Unit 2. Cellular Organization

A. In homologous introns, the pattern of divergence involves both changes in length.

B. Divergence in introns is due to deletions and insertions and base substitutions. 

C. Introns are slowly evolve while exons much more rapidly 

D. When a gene is compared among different species, there are instances where its exons are homologous but its introns have diverged so much that very little homology is retained.

TLS Online TPP Program

#Question id: 33482

#Unit 2. Cellular Organization

Find true and false statements

A. In general, mutations occur at the same rate in both exons and introns, 

B. Exon mutations are eliminated more effectively by selection.

C. Introns may more freely accumulate point substitutions and other changes.

TLS Online TPP Program

#Question id: 33483

#Unit 2. Cellular Organization

Which of the following is correct

A. A set of homologous genes should share common features that preceded their evolutionary separation.

B. All globin genes have a common form of organization with four exons and one introns.

C. A gene family is defined as a group of genes that encode related or identical products as a result of gene-duplication events.