Chapter Study Questions

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Chapter 15

Chapter Study Questions

This activity contains 16 questions.

Match the key terms in this chapter listed below with the phrase that is the best match for it.

Using the pull-down menus, match each item in the left column to the corresponding item in the right column.


	C-value paradox

	endosymbiosis

	lateral gene transfer, or horizontal gene transfer

	methylation

	secondary endosymbiosis

	exon shuffling

1.1 the addition of -CH_₃ groups to certain parts of DNA, often to "silence" genes

1.2 combination of the coding sequences of genes in new ways

1.3 movement of genes from one species to another

1.4 a symbiotic relationship in which a single cell is engulfed and lives within a host cell

1.5 a symbiotic relationship in which a host cell, containing a smaller cell, is itself engulfed by a third cell

1.6 the puzzling observation that the amount of DNA per cell does not correlate with the size or complexity of the organism

In humans, about (1%, 8%, 44%, 82%) of the genome consists of DNA sequences that code for proteins, and close to (1%, 8%, 44%, 82%) consists of transposable genetic elements. On the available evidence, it appears that this [is / is not ] typical for eukaryotic genomes in general, and for mammal genomes in particular.

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Some of the options below regarding transposable elements are correct and some are not. Decide whether each statement is correct or incorrect.

Transposable elements spread more effectively in bacterial plasmids than in bacterial chromosomes. Transposable elements are found in greatest density in heterochromatin near the telomere. Transposable elements are an example of "selfish genes." Transposable elements can cause knock-out mutations. Transposable elements spread more effectively in organisms that reproduce asexually. Transposable elements will be favored by natural selection when they spread efficiently with high fitness cost to their hosts.

What do telomerase and the RAG enzymes have in common? Decide which of the following statements are correct.

They defend eukaryotic genomes against the actions of transposable elements. They are coded for by genes that were probably derived from transposable elements. They represent "domesticated" transposable elements that work for the benefit of their host. They methylate regions of DNA to prevent excessive copying by transposable elements. They defend bacterial genomes against transposable elements.

Two of the following statements correctly describe why transposable elements are found in greatest density in heterochromatin near the centromere. Which two?

They rarely cause knock-out mutations near the centromere because there are few coding sequences here. They multiply more effectively near the centromere. They preferentially insert in heterochromatin. They are not eliminated by purifying selection in this location. They are protected from editing when they are surrounded by other transposable elements.

Name and briefly describe the four mechanisms of lateral gene transfer. Which one has been responsible for most cases of lateral gene transfer in eukaryotes?

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What was unusual about the transposable elements in the hybrid wallaby studied by O'Neill et al., and why did it occur?

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Four of the following statements correctly describe signs of lateral gene transfer of a particular gene, which two are incorrect. Which are correct?

Location of the gene near the centromere. Occurrence of methylation that silences the gene. A GC to AT ratio that is unusual for the host species. Phylogenetic analysis that assigns the gene to another clade. Usage of codons that are uncommon in the host species. Presence of nearby transposase genes or viral insertion sequences.

Two of the following statements represent evidence that mitochondria and chloroplasts are derived from endosymbiotic bacteria. The other three are incorrect. Paying attention to the details of each statement, decide which are correct.

Both organelles have a bacterial-like circular chromosome with abundant histone proteins. Both organelles have a triple membrane, such as would be formed by engulfing of a bacterium by a host cell. Phylogenetic analyses place mitochondrial genes within the alpha-proteobacteria. Phylogenetic analyses place chloroplast genes within the archaea. Both organelles are approximately the size of a bacterial cell.

Are transposable elements ever beneficial for their hosts? Explain and give examples.

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Summarize the eventual fate of genes of a endosymbiotic bacterium that has been engulfed by a host cell and is taking up permanent residence in that host lineage. How many genes did the ancestors of chloroplasts and mitochondria probably have? What has happened to most of these genes? Give some examples of specific genes.

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Why do parasites have small genomes?

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Are the striking phenotypic differences between humans and chimpanzees thought to be due to the presence of different genes or different proteins in the two species? Why or why not?

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Which statements correctly summarize findings from environmental sequencing studies?

Sargasso Sea samples contain numerous genes for degrading urea. Whale carcass environments contain diverse genes for proteorhodopsins. Soil samples contain abundant genes for degrading cellulose. Environmental sequencing has led to the discovery of a major clade of marine bacteria. Diatoms have genes for the complete urea cycle.

Suppose you are studying a unusual photosynthetic fungus. You discover that its photosynthetic enzymes occur within a small organelle that is bounded by four membranes. What is the likely source of each of the four membranes? How did this fungus probably acquire the ability to photosynthesize? What other evidence could you look for to test your ideas?

To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

In the 1980s, cow cells were found to contain an abundant class of LINEs that were called Bovine-B, or Bov-B, LINEs. Bov-B LINEs are now known to be present in all ruminants (cows, antelopes, goats, deer, etc.), and, oddly, in all snakes and a few lizards. Bov-B LINEs do not occur in turtles, crocodiles, humans, mice, chickens, frogs, zebrafish, spiders, or plants. Bov-B sequences of lizards and snakes are more diverse than are Bov-B sequences of ruminants. Phylogenetic analyses show that the Bov-B LINEs of ruminants nest within the Bov-B LINEs found in snakes, and are mostly closely related to the Bov-B LINEs of colubrid snakes.

Part I: Refer to the paragraph above in answering this question: Why do Bov-B LINEs occur in these two groups of vertebrates but not in any others? How do you think the Bov-B LINEs were transmitted to these two groups?

Part II: Refer to the paragraph above on the Bovine-B cows to answer this question: All vertebrates have a protein involved in embryological development of the cranium and face. This protein, called bucentaur, is coded for by the gene bcnt. Ruminants have two copies of this gene. One appears to be a typical bcnt gene. The other includes a stretch of sequence similar to a piece of a Bov-B LINE. This gene is actively expressed in ruminant development, and may have contributed to the adaptive radiation of the ruminants. Develop a hypothesis for the origin of the second bcnt gene.

To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

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