The convergence in external morphology of dolphins and tuna is attributed to
a. reduced genetic variability in these groups.
b. selection pressures that are common to these groups.
c. reproductive isolation of these groups.
d. identical genes in all three groups.
e. genetic mutation.
B
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Some bacteria are metabolically active in hot springs because _____
A) they are able to maintain a lower internal temperature B) high temperatures make catalysis unnecessary C) their enzymes have high optimal temperatures D) their enzymes are completely insensitive to temperature E) they use molecules other than proteins or RNAs as their main catalysts
A polysome is
a. one of the units of a ribosome. b. the nuclear organelle that synthesizes RNA. c. an organelle that functions similarly to a ribosome during meiosis. d. the two units of a ribosome considered together. e. an mRNA molecule with several ribosomes attached.
In pea plants, round peas are dominant (R) and shriveled peas are recessive (r), and yellow peas (shown as light gray in the Punnett square) are dominant (Y) and green peas (dark gray) are recessive (y). Using this information and the partial Punnett
square shown, what phenotype should be in the square labeled B? A) round and yellow B) shriveled and yellow C) shriveled and green D) round and green
Most eukaryotic cells only express 20–30% of the genes they possess. The formation of heterochromatin maintains the other genes in a transcriptionally silent (unexpressed) state
Which histone modification directs the formation of the most common type of heterochromatin? (a) H3 lysine 4 methylation (b) H3 lysine 9 methylation (c) H3 lysine 14 methylation (d) H3 lysine 27 methylation