How does crossing-over during meiosis contribute to genetic variation?
A. Each cell created has chromosomes only from a single parent.
B. Crossing-over always causes loss of some genetic information.
C. Because genes will be in a new order on some chromosomes,additional DNA will need to be made.
D. The exchange of genetic material between homologous chromosomes means that a single chromosome now combines genetic information from both parents.
Ans: D. The exchange of genetic material between homologous chromosomes means that a single chromosome now combines genetic information from both parents.
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Organisms that do not require oxygen for growth but grow better in its presence are called
A. anoxygenic. B. facultative anaerobes. C. microaerophiles. D. aerotolerant.
In a population of bacteria, about 25 percent of the population has resistance to the antibiotic
penicillin. After a few days, 50 percent of the population has the resistant gene. Assume the population did not simply reproduce. How might this antibiotic resistance have spread in the population?
a. The gene for antibiotic resistance is found in plasmids, which can be transferred between bacteria. b. Bacteria are able to swap genes between their nucleoid and plasmids. c. The antibiotic must have been introduced into the population, which then evolved by natural selection. d. Genetic material in the nucleoid is shared among the population of bacteria.
When were the oldest stromatolites formed?
a. about 2.1 billion years ago b. about 3.5 billion years ago c. about 3.9 billion years ago d. about 4.2 billion years ago
The cellular machinery that replicates DNA inserts an incorrect base
a. roughly once in every 10 million bases b. roughly once in every million bases c. most of the time d. about half the time