MCAT Content / Evolution / Evolutionary Time As Measured By Gradual Random Changes In Genome

Evolutionary time as measured by gradual random changes in genome

Topic: Evolution

The molecular clock uses a constant rate of random change or mutation in a genome to estimate the evolutionary time or the time when the different species diverged.

Over time, genetic drift and factors, such as mutation, occur randomly at a constant rate in a population that can lead to significant changes in the genome of a population. These random mutations in a genome can be used to estimate or find out how long ago different species diverged. This concept is called “molecular clocks”. For example, in divergent evolution, new species develop from a common ancestor due to the evolution and accumulation of differences resulting in the formation of new species. This change may have been driven in response to changes in abiotic factors, such as a change in environmental conditions. These events can be measured by piecing together genetic and fossil evidence to create a molecular clock entry for each event. 

The molecular clock uses a constant rate of evolution in some genes to estimate the absolute time of evolutionary change.

Practice Questions

Khan Academy

MCAT Official Prep (AAMC)

Biology Question Pack, Vol. 1 Passage 13 Question 86

Key Points

• Genetic drift and factors, such as mutations that occur randomly at a constant rate in a population can be used to estimate or find out the evolutionary time or how long ago different species diverged; this is called the molecular clock.

Key Terms

evolution: the change in the genetic composition of a population over successive generations

molecular clocks: a figurative term for a technique that uses the mutation rate in a genome to deduce the time in prehistory when two or more life forms diverged

genetic drift: variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.

diverged: when a species separate from the same evolutionary route

mutation: the changing of the structure of a gene, resulting in a variant form that may be transmitted to subsequent generations, caused by the alteration of DNA

genome: the haploid set of chromosomes in a gamete or microorganism, or in each cell of a multicellular organism.

divergent evolution: the process whereby groups from the same common ancestor evolve and accumulate differences forming new species

abiotic factors: a factor in an environment which is not living which affects a population

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