In eukaryotic cells, transcription cannot begin until
A. several transcription factors have bound to the promoter.
B. the 5' caps are removed from the mRNA.
C. DNA nucleases have isolated the transcription unit.
D. the two DNA strands have completely separated and exposed the promoter.
E. the DNA introns are removed from the template.
Ans: A. several transcription factors have bound to the promoter.
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Answer the following statement true (T) or false (F)
The North American maggot fly diverged into two species because some individuals fed on apples rather than hawthorn trees. Apple fruit mature more quickly than hawthorn fruit, therefore maggot flies that fed on apples also developed more quickly. Pea aphids can feed on alfalfa or red clover; some aphids have higher fitness when eating clover others when eating alfalfa. Host preference can
eventually lead to speciation because A. genetic differences develop. B. lower fitness may result from choosing the wrong host. C. temporal isolation may occur. D. anagenesis may occur. E. genetic differences develop, higher fitness and temporal isolation may occur.
This tissue gives pear flesh a gritty texture and makes seed coats hard:
a. xylem b. collenchyma c. phloem d. sclerenchyma e. parenchyma
Which of the following contributes to the invasiveness of Treponema pallidum?
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