Table of Contents

Introduction

A molecular clock is a concept used to estimate the genetic divergences between species. It helps to analyze the mutation rates in DNA sequences and to find a common ancestor in them. It is used to study the history of human evolution and to find the connecting link between plants and animals.

The molecular clock also allows scientists to understand the evolutionary changes as well as determine the connecting ancestor between species. The study of these changes is known as the study of molecular evolution.

Evolution is defined as alteration in DNA, RNA, and protein molecules. They are affected by factors like mutation, genetic drift, and natural selection. It is also related to the patterns and processes of change that result in these different sequences.

Mutations are of two types

Heritable mutations – Occurs only in the germ line and are passed to the genomic sequence of the offspring.
Somatic mutations – Occurs during cell division promoting normal growth and development.

Molecular evolutionary studies focus only on heritable genetic changes that accumulate within and between organisms.

Molecular clock in evolutionary biology

The notion of time in evolution

Molecular clocks are calibrated to give accurate measurements in a particular time scale. It is generally done by collecting information about the absolute time ages.

The approximation of evolutionary durations from gene data involves the use of different methods. The comparison of different patterns of evolutionary variations helps in understanding molecular clock studies.

The evaluations are experimental studies on fossil or geological evidence and their impacts in terms of evolutionary timescales.

Hypothesis and its importance

The molecular clock hypothesis was given by Zuckerkandl and Pauling based on certain calibrations. These calibrations are the study of fossil or geological evidence, and their selections have great impacts on molecular estimates of evolutionary relationships. It has become an important key in evolutionary biology that defines DNA and protein sequences evolve at a constant rate over time.

The molecular clock can be explained with the help of phylogenetic tree diagrams. They are branching pictorial representations that depict the history and evolutionary relationship of organisms or groups of species.

The procedure of estimating a molecular clock includes

Find the number of alterations in the nucleotide sequences.
To keep a note of the fossils and find a link of the common ancestor between organisms.
Determination of evolutionary ratio and morphological divergences for the new sequences.

Mechanism of molecular clock

Substitution rate and genetic mutation

The molecular clock is a clock mechanism, used to calculate the divergence between the different organisms mainly based on their genetic resemblances. They are generally based on the feedback mechanism.

The working principle of the gene clock is to assume that mutations occur at a steady rate and to calculate the time when two organisms had to share a common ancestor to have an assemblage of the same mutations.

Researchers then estimate the exact date when two ancestries diverged from one another, thus providing valuable information regarding their evolutionary history.

Calculating evolution rates precisely with this method requires the occurrence knowledge of both the proceedings like speciation and type of mutations that occurred during that time frame.

This knowledge is gained through proper examination of particular genomes at specific regions to incorporate changes according to ancestral conditions at different evolution points.

Influence of natural selection and genetic drift

Natural selection and genetic drift play an important influence on the gene clock. Natural selection is a method of survival mechanism with the help of which organisms adapt and evolve according to environmental needs. Hence, certain traits evolve and appear similar with time.

Giraffes’ long neck has evolved along with time and has proven a significant increase in their survival rates.

Genetic drift refers to random occurrences in gene frequencies due to random events in a stable population of species.

These processes influence the rate at which mutations are introduced into the populations, thus affecting the precision of the gene clock.

Moreover, natural selection also affects how rapidly new organisms evolve from their existing self. It favors the survival rate of individuals that are better adapted to their environment. Few species can adapt faster than others depending upon suitable environmental conditions and ancestry lineage.

Genetic drift causes alterations in allele frequencies between different populations or even within the same population over time. It results in changes in the mutation ratio across different lineages, thus creating a great impact on the accuracy of the molecular clock.

Types of molecular clock

1. Nucleotide substitution clock (Mitochondrial DNA and nuclear DNA clock)

This clock is used to estimate the rate of genetic evolution. Several substitutions in DNA sequences over time are used to check mutation changes.

They are widely used by scientists for studying molecular changes and a better understanding of population genetics. This technique deals with random mutations in a DNA sequence.

2. Amino acid substitution clock

This clock is used to calculate the time between two species that show divergence from their common ancestor.

This methodology is based on the evolution of proteins at different rates and estimated accordingly. This technique helps the researchers to understand the time of evolutionary rates between species.

Calibration and calibration point

Researchers use sample data to calibrate the evolutionary events chronologically. They are studied to find out a common ancestor and to detect the number of substitutions used in a nucleotide sequence. These data are used in the calibration of the divergence time of particular taxa.

1. Fossils as calibration

Fossils are the dead and buried remains of organisms in sedimentary rocks that are used for research purposes. These fossils are calibrated to understand the dating of gene clocks and play a major role in the estimation of genetic divergences.

2. Geological events as calibration

Geological events are a tool to calibrate the geo-history. Scientific models are used to calibrate data and to accurately identify geological events that took place on the earth’s surface. These findings also allow us to understand environmental states and their effects on the evolution of a species.

Application of molecular clocks

Gene clock is a method used to calculate the differences in time between two particular species. This concept involves gene mutations occurring at a constant rate over time and continuous calibration of divergences between species.

The application of this technique has been widely used:

In evolutionary biology
Population genetics and phylogenetics
Molecular clocks are commonly used to study evolution that share a common ancestor.
In epidemiology, to track disease outbreaks and identify new pathogens.
Anthropology, to detect human migration patterns.

Factors influencing the molecular clock

The substitution rate in the nucleotide sequence of an organism. High mutation rates lead to the consumption of more time and chances of low accuracy.
Population size is the next factor that affects the accuracy. Large populations cause large genetic drift, thus high chances of error.
Climatic conditions such as temperature and humidity influence quick mutations in the genome sequence that become difficult to deal with.

Comparison of a molecular clock with other phylogenetic methods

Molecular clocks and phylogenetic methods are methods to study mutative relationships between species.

Time measurement

Molecular clocks use markers to identify gene mutations, whereas phylogenetics uses morphological features to analyze. They focus on the interspecies relationship to estimate differences.

Future perspectives

Molecular clocks prove an important tool in estimating the time-lapse of evolutionary data. The accuracy of molecular clocks has improved significantly over the past few years, because of several advancements.

Accuracy of calibration technique using fossil remains that are used as evidence.
High-efficiency algorithm data used in genome sequencing, improved results.
Algorithms have improved in determining the divergence in species with ease.
Single gene analysis has a significant achievement in uncovering discoveries.

Q&A

1. What is the molecular clock in simple terms?

It is also called a gene clock that is used in evolutionary biology and population genetics. Molecular clocks are used to calibrate the period between two particular species to figure out a common ancestry.

2. What is an example of a molecular clock?

It is a technique based on their genetic similarity. Suppose, species are found to have a 20% difference in their DNA substitution sequences, it can be predicted that these two species come from a common ancestor of about 2% divergence nearly 5 mya.

3. Which RNA is the molecular clock?

tRNA molecular clocks are used in the case study of molecular clocks. TRNAs are generally single-stranded RNAs used during protein synthesis. Thus, it proves to be a great tool in the estimation of mutation rates in molecular clocks.

4. What is the molecular clock for humans?

A molecular clock for humans is a method of estimating the time at which certain genetic events occurred in human evolution. This technique uses DNA sequences from different species to estimate when two lineages diverged and to have a clearer view of population dynamics.

Summary

The molecular clock hypothesis was given by Zuckerkandl and Pauling.
It is also called a gene clock that is used in evolutionary biology and population genetics.
Molecular clocks are used to calibrate the period between two particular species to figure out a common ancestry.
Natural selection and genetic drift play an important influence on the gene clock.
Genetic drift causes alterations in allele frequencies between different populations or even within the same population.
Fossils are used to understand the dating of gene clocks.
One of the major applications of epidemiology is to track disease outbreaks and identify new pathogens.
In the case of humans, this technique uses DNA sequences from different species to estimate when two lineages diverged and to have a clearer view of population dynamics.
It has become an important key in evolutionary biology that defines DNA and protein sequences evolve at a constant rate over time.
Hence, molecular clocks are used to study the history of human evolution and to find the connecting link between plants and animals.

Molecular Clock