Question: What is meant by the term “molecular clock”? What are the basic assumptions by which it is presumed to operate? How have data from molecular clock analyses been used?
Solution: MOLECULAR CLOCK:-
The molecular clock is defined as a technique that helps to detect the geological time or era in which two species or taxa diverged from the parent species. This technique uses the rates of molecular changes and other fossil characteristics to determine the geological time.
ASSUMPTION ARE OPERATION::
the molecular clock has become an essential tool in many areas of evolutionary biology, including systematics, molecular ecology, and conservation genetics. The molecular clock hypothesis states that DNA and proteinsequences evolve at a rate that is relatively constant over time and among different organisms. A direct consequence of this constancy is that the genetic difference between any two speciesis proportional to the time since these species last shared a common ancestor. Therefore, if the molecular clock hypothesis holds true, this hypothesis serves as an extremely useful method for estimating evolutionary timescales. This is of particular value when studying organisms that have left few traces of their biological history in the fossil record, such as flatworms and viruses.
The molecular clock is figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistorywhen two or more life forms diverged. The biomolecular data used for such calculations are usually nucleotide sequences for DNA or amino acid sequences for proteins. The benchmarks for determining the mutation rate are often fossil or archaeological dates. The molecular clock was first tested in 1962 on the hemoglobin protein variants of various animals, and is commonly used in molecular evolution to estimate times of speciation or radiation.
It is sometimes called as gene clock or an evolutionary clock.
ANALYSIS USES ::
The molecular clock technique is an important tool in molecular systematics, the use of molecular genetics information to determine the correct scientific classificationof organisms or to study variation in selective forces. Knowledge of approximately constant rate of molecular evolution in particular sets of lineages also facilitates establishing the dates of phylogenetic events, including those not documented by fossils, such as the divergence of living taxa and the formation of the phylogenetic tree. In these cases—especially over long stretches of time—the limitations of MCH (above) must be considered; such estimates may be off by 50% or more.
