Why is an AT-rich sequence characteristic of DNA replicators in all organisms?
What will be an ideal response?
AT-rich regions of DNA are relatively easy to denature to single strands. AT base pairs are held together by only two hydrogen bonds, while GC pairs are held together by three.
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What is the nature of the genetic mutation that causes lactose intolerance?
A. It is a dominant mutation that prevents lactase production. B. It is a dominant mutation that causes a decline in adult lactase levels. C. It is a recessive mutation that prevents lactase production. D. It is a recessive mutation that causes a decline in adult lactase levels. E. It is an X-linked mutation that prevents lactase production.
Bacteria cannot be classified using the biological definition of a species for which reason?
A. The DNA sequences of all bacteria are more than 97% identical. B. Bacteria cannot reproduce. C. Bacteria are present everywhere and cannot be reproductively isolated from other bacteria. D. Bacteria are asexual. E. Bacteria do not evolve.
Although the United States only holds 4% of the world's population, what percentage of carbon dioxide emissions are produced in the United States?
Why did the dinosaurs become extinct?
A. The pollen produced by the rise in flowering plants produced allergenic responses in dinosaurs and interfered with their ability to communicate with potential mates. B. Increasing carbon dioxide levels produced climates too hot for the incubation of their eggs. C. Cycads and other gymnosperms upon which herbivorous dinosaurs fed declined, and the dinosaurs were unable to digest the angiosperms that arose in their place. D. A meteorite or comet crashed into the Earth, causing smoke and ash that blocked the sun and caused death of the plants that were food for herbivorous dinosaurs. E. The changing climate caused the evolution of most dinosaur species into the existing bird, mammal, and reptile species that exist today.