PrepTest 121, Section 3, Question 20
The first thing any embryo must do before(467 more words not shown)
Which one of the following(9 more words not shown)
- ASpecies differ more(19 more words not shown)
- BEmbryos determine their(21 more words not shown)
- CWhile very similar(27 more words not shown)
- DThe mechanisms by(30 more words not shown)
- EDespite their apparent(19 more words not shown)
Reading the passage
We've already predicted the contrast: early polarity varies substantially across species, while later development uses remarkably similar genes. We need both sides of that comparison. The examples of flies, worms, and mammals explain it.
Working the answers
- A
Overall genetic makeup is not the comparison. The writer contrasts mechanisms for establishing polarity with those used in later development, not with every genetic difference between species.
- B
Simpler and more complex vertebrates are mentioned, but the account doesn't divide all organisms into two groups with a method assigned to each. This replaces the broad diversity with a rule we weren't given.
- CCorrect
It pairs similar genes in later development with dramatically different mechanisms for establishing polarity. That matches our prediction and the final paragraph's apparent paradox.
- D
This is too narrow and misstates the nematode mechanism. Its p-granules are initially in the egg's cytoplasm, not described as granules of the sperm. The overall discussion also includes the still-unexplained mammalian process.
- E
This reverses the central claim. The mechanisms for establishing polarity are different. The striking similarities concern later development.
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