alleryStart learning →Nucleotide doublets were rejected as the coding unit because they allow only how many combinations?
AFour possible combinations
BTwenty possible combinations
CSixty-four combinations
DSixteen possible combinations
Answer & Solution
Correct answer: D. Sixteen possible combinations
1. Four bases taken two at a time give 4 times 4, which is 16 possible doublets.
2. Sixteen combinations cannot cover 20 amino acids, so doublets were ruled out.
3. Four bases taken three at a time give 64 combinations, which is more than enough.
4. Twenty is the number of amino acids to be specified, not the number of doublets available.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 15 "Genes and Proteins", section 15.1 The Genetic Code_
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