Parallelism is a literary and grammatical device that is extremely effective in communcation as it arranges ideas in an orderly and logical pattern, a pattern which allows the reader's or listener's mind to quickly grasp the idea(s) that the writer states. Thus, the use of similar grammatical constructions such as single words like nouns or adjectives, or phrases such as participial phrases, verb phrases, and gerund phrases, or clauses enables the reader to recognize the comparison or contrast of ideas that are being presented. This use of parallelism is extremely important in the writing of paragraphs and essays, particularly in the thesis statement of an essay. In addition, parallelism is also a very effective tool in argumentative or rhetorical writing.
In the above mentioned sentence,
People differ in their fingerprint patterns, in how they talk, and in their dental patterns.
the second phrase differs from the others as it is abverbial. So, it can be corrected by repeating the word pattern which is used in the other two phrases:
A. People differ in their fingerprint patterns, their speech patterns, and their dental patterns.
In English, it is not necessary to repeat the word in as the reader understands that they are implied. However, you may wish to include them:
B. People differ in their fingerprint patterns, in their speech patterns, and in their dental patterns.