With respect to the DNA methylation mechanism in mammalian cells, which of the following statements, if any, is true? 

I. The principal role of the DNMT1 DNA methyltransferase is in de novo methylation. 

II. The DNMT3A and DNMT3B DNA methyltransferases require hemi-methylated DNA as a substrate and are responsible for methylating nascent DNA strands that are complementary to methylated parental DNA strands.

III. Active DNA demethylation means removal of methyl groups from a hemi-methylated DNA double helix. 

IV. DNA methylation is not essential in mammalian development.

#Question id: 9212

#Unit 9. Evolution & Diversity of Life Forms

Burning fossil fuels releases oxides of sulfur and nitrogen. These air pollutants can be responsible for ________.

#Question id: 9213

#Unit 9. Evolution & Diversity of Life Forms

Suppose you attend a town meeting at which some experts tell the audience that they have performed a cost-benefit analysis of a proposed transit system that would probably reduce overall air pollution and fossil fuel consumption. The analysis, however, reveals that ticket prices will not cover the cost of operating the system when fuel, wages, and equipment are taken into account. As a biologist, you know that if ecosystem services had been included in the analysis, the experts might have arrived at a different answer. Why are ecosystem services rarely included in economic analyses?

#Question id: 9214

#Unit 9. Evolution & Diversity of Life Forms

Researchers have been studying a rare population of 87 voles in an isolated area. Ten voles from a larger population were added to this isolated population. Besides having ten additional animals, what benefits are there to importing individuals?

#Question id: 9215

#Unit 9. Evolution & Diversity of Life Forms

Use the following figure to answer the question

Five new individuals were added to a small population of bighorn sheep in 1986, and ten more were added between 1990 and 1994. According to the figure, what occurred in this population after these additions?

#Question id: 9216

#Unit 9. Evolution & Diversity of Life Forms

Which of the following criteria have to be met for a species to qualify as invasive?

#Question id: 9217

#Unit 9. Evolution & Diversity of Life Forms

Which of the following conditions is the most likely indicator of a population in an extinction vortex?