Compare and contrast the three hypotheses which explain the evolution of viruses What will be an ideal response?
CONCEPTS TO CONSIDER:According
to the progressive, or escape, hypothesis, viruses may have originated as mobile
genetic elements that could have escaped and moved from one cell and entered another
through damaged cell membranes. Viruses may trace their origin to animal cells, plant cells,
bacterial cells, or archaeal cells. The regressive, or reduction, hypothesis asserts that
viruses are remnants of cellular organisms; they evolved from free-living, complex cellular
ancestors. As they became parasitic, the viruses gradually lost some of the genes necessary
for protein synthesis. Genes they no longer needed, like those for protein synthesis, were
gradually lost through evolution. According to the virus-first hypothesis, viruses predate or
coevolved with their current cellular hosts. Viruses may have initially existed as selfreplicating
units. As they evolved, viruses produced enzymes for the synthesis of membranes
and cell walls, leading to the formation of the first cells.
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Which of the following is not a characteristic of Saccharomyces cultures?
a. The cells are haploid. b. The cells have a relatively short generation time. c. Cells reproduce asexually by budding. d. The cells can be induced to reproduce sexually. e. All answers are true of Saccharomyces cultures.
In the experiment in which Frye and Edidin fused the plasma membranes of a mouse and a human cell, what happened
to the membrane proteins? a. They formed a bilayer. b. They formed a spherical structure. c. They moved laterally across the cell surface. d. They flip-flopped from one layer to the other. e. They reacted with cholesterol molecules on the membrane surface.
The evolution of seeds allowed for:
a. the development of an independent sporophyte. b. coevolution with animal pollinators. c. heterospory—the development of male and female gametophytes. d. plants to colonize dryer climates. e. All of the above are correct.
The two strands of DNA are held together by hydrogen bonds
Indicate whether the statement is true or false