You are studying regulation of the yeast enzyme glutamine synthetase (GS), which is encoded by the GLN1 gene. You have isolated two mutants, designated  gln2– and gln3–, that give decreased GS activity. Mating of either gln2– or gln3– haploids to wild type produces heterozygous diploids that show normal amounts of GS expression. When you cross either a gln2– or gln3– haploid to a gln1– strain the resulting diploids show normal expression of GS.

The GLN1 gene shows a rather complex regulation in response to different amino acids. When either glutamate (glu) or glutamine (gln) is added to the medium, the amount of GS expression diminished and when both glutamate and glutamine are added to the medium GS expression is shut off completely. The effects of different mutants on the response to glu and gln are shown below.

Which of the models from best fits these experimental results? Complete the model for the regulation of GLN1 that includes the effects of glu and gln.      

TLS Online TPP Program

#Question id: 8922

#Unit 9. Evolution & Diversity of Life Forms

Which statement is most consistent with the hypothesis that the Cambrian explosion was caused by the rise of predator-prey relationships?

TLS Online TPP Program

#Question id: 8923

#Unit 9. Evolution & Diversity of Life Forms

Which of these genetic processes may be most helpful in accounting for the Cambrian explosion?

TLS Online TPP Program

#Question id: 8924

#Unit 9. Evolution & Diversity of Life Forms

Fossil evidence indicates that the following events occurred in what sequence, from earliest to most recent?

1. Protostomes invade terrestrial environments.

2. Cambrian explosion occurs.

3. Deuterostomes invade terrestrial environments.

4. Vertebrates become top predators in the seas.

TLS Online TPP Program

#Question id: 8925

#Unit 9. Evolution & Diversity of Life Forms

What is the probable sequence in which the following clades of animals originated, from earliest to most recent?

1. tetrapods

2. vertebrates

3. deuterostomes

4. amniotes

5. bilaterians

TLS Online TPP Program

#Question id: 8926

#Unit 9. Evolution & Diversity of Life Forms

Sponges and cnidarians are among the fossilized animals found in both the Ediacara Hills and the Burgess Shale from the Rocky Mountains of British Colombia. This observation requires that

TLS Online TPP Program

#Question id: 8927

#Unit 9. Evolution & Diversity of Life Forms

Arthropods invaded land about 100 million years before vertebrates did so. This most clearly implies that