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Related Concept Videos

Biological Clocks and Seasonal Responses02:45

Biological Clocks and Seasonal Responses

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The circadian—or biological—clock is an intrinsic, timekeeping, molecular mechanism that allows plants to coordinate physiological activities over 24-hour cycles called circadian rhythms. Photoperiodism is a collective term for the biological responses of plants to variations in the relative lengths of dark and light periods. The period of light-exposure is called the photoperiod.
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Generation Time01:22

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Bacterial generation time, the period required for a bacterial population to double during its exponential growth phase, serves as a critical measure of microbial growth dynamics under optimal conditions. This parameter varies significantly across bacterial species and can be influenced by factors such as temperature, pH, and the availability of nutrients. For example, Escherichia coli can achieve a generation time of approximately 20 minutes, while Mycobacterium tuberculosis exhibits a much...
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The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent...
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Lagging Strand Synthesis01:59

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During replication, the complementary strands in double-stranded DNA are synthesized at different rates. Replication first begins on the leading strand. Replication starts later, occurs more slowly, and proceeds discontinuously on the lagging strand.
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Circadian rhythms are cyclic changes that are crucial in plasma drug concentrations. Various standard circadian parameters, including core body temperature, heart rate, and other cardiovascular factors, directly impact disease states and the therapeutic response to drug therapy.
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John H. Renwick first coined the term “synteny” in 1971, which refers to the genes present on the same chromosomes, even if they are not genetically linked. The species with common ancestry tend to show conserved syntenic regions. Therefore, the concept of synteny is nowadays used to describe the evolutionary relationship between species.
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Related Experiment Videos

The molecular clock may be an episodic clock.

J H Gillespie

    Proceedings of the National Academy of Sciences of the United States of America
    |December 1, 1984
    PubMed
    Summary

    Molecular evolution is not constant but episodic, occurring in rapid bursts followed by long, slow periods. This challenges the neutral allele theory and the standard molecular clock interpretation.

    Area of Science:

    • Evolutionary biology
    • Molecular evolution
    • Genetics

    Background:

    • The perceived constant rate of molecular evolution is a long-standing observation in evolutionary biology.
    • This constancy has been interpreted through the lens of the neutral allele theory and the molecular clock hypothesis.
    • However, the slow rate of individual amino acid evolution raises questions about this interpretation.

    Purpose of the Study:

    • To investigate the dynamics of molecular evolution.
    • To test whether the rate of molecular evolution is truly constant or episodic.
    • To re-evaluate the compatibility of observed evolutionary dynamics with the neutral allele theory and the molecular clock.

    Main Methods:

    • Statistical analysis of protein evolution data.

    Related Experiment Videos

  • Application of a stationary point process as a null hypothesis.
  • Modeling molecular evolution dynamics.

    • Main Results:

    • The study concludes that molecular evolution is episodic, not constant.
    • Evidence suggests short, rapid bursts of evolution interspersed with long periods of stasis.
    • The observed episodic dynamics are inconsistent with a stationary process.

    Conclusions:

    • The apparent constancy of molecular evolution is likely an artifact of slow individual amino acid evolution.
    • Molecular evolution proceeds in episodic bursts, challenging the neutral theory.
    • A revision of the standard interpretation of the molecular clock is necessary based on these findings.