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Question

Difficulty: MediumPunctuation of Nonessential Elements

The passage below contains a blank. Based on the rules of Standard English conventions, which punctuation mark should fill the blank to correctly set off the nonessential element?

Answer:In the 1940s, geneticist Barbara McClintock studied maize plants to understand inheritance patterns. Her research on transposons, which are genetic elements that can change positions within a genome【,】 ultimately challenged the prevailing scientific belief that genes were fixed in place on chromosomes.

Answer

A comma (,) must be placed in the blank to complete the punctuation pair setting off the nonessential element.
The sentence contains the nonessential relative clause 'which are genetic elements that can change positions within a genome,' which modifies the noun 'transposons.' Standard English conventions require nonessential elements to be set off by matching pairs of punctuation. Because the clause is introduced with a comma after 'transposons,' it must close with a matching comma after 'genome' before the sentence continues with the main verb 'ultimately.'

Step-by-Step Solution

1
Identify the nonessential element in the sentence.
The clause 'which are genetic elements that can change positions within a genome' is a nonessential relative clause modifying the noun 'transposons'.
This clause provides descriptive details about transposons but is not grammatically necessary for the main clause of the sentence.
2
Examine the punctuation currently used to introduce the nonessential element.
The nonessential clause begins with a comma after the word 'transposons'.
Nonessential elements must be set off from the rest of the sentence using matching pairs of punctuation, such as two commas, two em dashes, or parentheses.
3
Determine the punctuation required to close the nonessential element.
A comma is required in the blank to match the opening comma.
Using any other punctuation mark, such as an em dash or parenthesis, would create asymmetrical punctuation, violating Standard English conventions.

Key Concept

Punctuation of Nonessential Elements
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Topics

Punctuation of Nonessential Elements

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