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.      

#Question id: 8715

#Unit 9. Diversity of Life Forms

Which of the following items is most likely to form a simple linear relationship with the number of gene-duplication events, when placed as the label on the vertical axis of the following graph?

#Question id: 8716

#Unit 9. Diversity of Life Forms

The most important feature that permits a gene to act as a molecular clock is ________.

#Question id: 8717

#Unit 9. Diversity of Life Forms

Molecular clocks are more reliable when ________.

#Question id: 8718

#Unit 9. Diversity of Life Forms

Which of the following would, if it had acted upon a gene, prevent this gene from acting as a reliable molecular clock?

#Question id: 8720

#Unit 9. Diversity of Life Forms

The question refers to the following table, which compares the percent sequence homology of four different parts (two introns and two exons) of a gene that is found in five different eukaryotic species. Each part is numbered to indicate its distance from the promoter (for example, Intron I is the one closest to the promoter). The data reported for species A were obtained by comparing DNA from one member of species A to another member of species A.

Which of these four gene parts should allow the construction of the most accurate phylogenetic tree, assuming that this is the only part of the gene that has acted as a reliable molecular clock?

#Question id: 8721

#Unit 9. Diversity of Life Forms

Based on cladistics, which eukaryotic kingdom is polyphyletic and, therefore, unacceptable?