Molecular clock

Molecular clock is a metaphor for a method that is used in genetics to determine the time of splitting of two species from a common ancestor with the help of DNA sequencing and estimate the evolution of time. The more mutations ( differences in the DNA sequence) have been created, the longer the development time lasted. It is difficult to determine the frequency of mutations ( the mutation rate ) and thus to calibrate the " transition speed " is the molecular clock.

Importance

The technique of molecular clock is an important tool in molecular genetics to classify the organisms and dated by evolutionary events.

Research and Calibration

The term molecular clock was introduced by Emile Zuckerkandl and Linus Pauling. You in 1962 noticed that the amino acids of hemoglobin were always different, the longer the duration of two separate evolutionary ways. They generalized their observations to the hypothesis that the mutation rate of any proteins during evolution is constant over time.

1967 Allan Wilson and Vincent Sarich turned this hypothesis in particular on the evolution of Hominini ( the immediate ancestors of man). Their time scale Sapiens 2012 was moved to a recalculation in particular for the development of Homo clearly older.

However, a temporarily increased selection pressure may have the effect that mutations rapidly prevail in a population and thus - at constant mutation rate - speed up the transition speed of the molecular clock. Motoo Kimura in 1968 observed that while many mutations change the DNA sequences, but does not affect the phenotype (neutral theory) and thus are not subject to selection. This evolutionarily neutral ' differences can be used to measure time. For calibration, we used as a reference species for which it was known the time of their split by fossil finds.

Francisco J. Ayala listed in 1999 on five factors that affect the transfer speed of the molecular clock:

• Generation time (the shorter the generation time, the faster mutations are fixed)
• Population size (the larger the population, the more mutations are selected against )
• Species-specific differences
• Function of a protein
• Change of natural selection ' (changing the read-out conditions )

According to Ayala researchers come to very different results, depending on the organisms and genes used. The different molecular clocks were inaccurate, despite more detailed analysis and better data. The clock speeds are still poorly understood.