molecular clock

noun
the changes in the amino acid sequences of proteins that take place during evolution and speciation, and from which the dates of branchings of taxonomic groups can be deduced.
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Main Entry:  molecular clock1
Part of Speech:  n
Definition:  a biological system that keeps time or pulses
Main Entry:  molecular clock2
Part of Speech:  n
Definition:  the rate at which nucleotide (amino acid) substitutions occur in a given DNA (protein) sequence
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Example sentences
When dating biological events, molecular geneticists rely on a concept known as the molecular clock.
Their closeness was brought home when the researchers constructed a molecular clock.
Second, one can use molecular clock methodologies to peg the timing of the separation between two clades.
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