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Difficulty: MediumCommas with Nonessential and Parenthetical Elements

In the 1940s, geneticist Barbara McClintock studied the inheritance patterns of maize plants. Her research on transposons, which are DNA sequences that can move within a genome, eventually earned her a Nobel Prize in Physiology or Medicine. This groundbreaking work challenged the long-held belief that genes were static entities on chromosomes.

Which choice best punctuates the underlined portion of the sentence?

  1. on transposons, which are DNA sequences that can move within a genome,Answer
  2. B
    on transposons, which are DNA sequences, that can move within a genome,
  3. C
    on transposons, which are DNA sequences that can move within a genome
  4. D
    on transposons; which are DNA sequences that can move within a genome,

Answer

on transposons, which are DNA sequences that can move within a genome,
The correct choice properly uses a comma before 'which' and a comma after 'genome' to enclose the nonessential relative clause 'which are DNA sequences that can move within a genome.' This clause provides descriptive details about 'transposons' but is not essential to the overall sentence structure.

Step-by-Step Solution

1
Identify the parenthetical or nonessential element in the sentence.
The phrase 'which are DNA sequences that can move within a genome' provides supplementary descriptive information about 'transposons.' The core sentence remains complete without it: 'Her research on transposons eventually earned her a Nobel Prize in Physiology or Medicine.'
Nonessential elements must be set off from the rest of the sentence by punctuation (typically commas).
2
Apply the appropriate punctuation rules for nonessential elements.
Since the nonessential element appears in the middle of the sentence, it must be enclosed by a pair of commas: one before 'which' and one after 'genome.'
Omitting one of the commas results in a dangling comma error, and using a semicolon instead of a comma incorrectly separates a dependent clause from its main clause.
3
Check the restrictive clause within the nonessential element.
The clause 'that can move within a genome' restricts 'DNA sequences' and should not be separated from it by a comma.
Restrictive clauses are essential to the meaning and must not be separated from their referent with commas.

Key Concept

Commas with Nonessential and Parenthetical Elements
Estimated Time:1m 0s
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Commas with Nonessential and Parenthetical Elements

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