Navigation Links
Muller's ratchet


In genetics, Muller's ratchet is a hypothesis that explains how functionally important genes may be lost when organism's genes are only transmitted vertically, without recombination caused by sex. Exclusive vertical transfer occurs when the organism is an endosymbiont, e.g. a bacterial endosymbiont of insects, which is only transmitted to offspring from the mother. Another example is mitochondria and chloroplasts, which are also transmitted only vertically (although, in this case, they are not generally considered a separate organism).

Muller's ratchet applies to any deleterious mutation that occurs in a vertically transmitted organism. It may be that the mutation is deleterious, but not lethal. Furthermore, the organism with the mutation may have another advantageous mutation -- or its host may have an advantageous mutation -- that will lead to their survival despite the deleterious mutation. Because there is no possibility for genetic mixing, e.g. through sexual reproduction, the organism's descendants have no opportunity to receive a good copy of the gene. If the other mutation is advantageous, their survival means that the deleterious mutation persists. These deleterious mutations resemble the operation of a ratchet, in that the organism can never go back.

By contrast, sexual reproduction allows most plants and animals to create offspring with good copies of two genes via crossover. That is, if one animal has the deleterious mutation in one gene and the advantageous mutation in another, while another animal has two normal copies of the gene, a mating of these animals can produce offspring with the advantageous mutation and without the deleterious one. Thus, a deleterious mutation coupled with an advantageous one can be undone in organisms with sexual reproduction. Horizontal gene transfer in bacteria allows a similar situation. Generally, only obligate endosymbionts, mitochondria and chloroplasts are exposed to Muller's ratchet. But even sexually reproducing organisms are exposed to Muller's ratchet in the case of single-copy chromosomes, such as the human Y chromosome.

Muller's ratchet is an important theory as to why sex evolved, but works better in small populations than larger ones. See the Red Queen for the hypothesis that is generally regarded as being superior, though note that the two are not mutually exclusive. Any discussion on the evolution of sex should include a discussion of the Muller's ratchet.

References

  • Muller, H.J. (1932). "Some Genetic Aspects of Sex". American Naturalist 66:118-138 (Muller's original paper)
  • Nancy A. Moran (1996), Accelerated evolution and Muller’s ratchet in endosymbiotic bacteria, Proceedings of the National Academy of Sciences USA, 93, pp. 2873-2878. [1] (An article that discusses Muller's ratchet in the context of endosymbiotic bacteria.)

'"/>


(Date:12/5/2014)... -- Tute Genomics, a leader in cloud-based solutions for genome ... led by UK-based Eurovestech. Peak Ventures and a number ... "We are at a pivotal time in ... seeks new approaches for the diagnosis, treatment and prevention ... and CEO of Tute Genomics. "One of the main ...
(Date:11/21/2014)... -- According to a new market research ... Access Control, Intrusion Detection, Parking Management, Under Vehicle Inspection), ... Geography - Global Forecasts to 2020", published by MarketsandMarkets, ... around $25 Billion in 2014 and is expected to ... of 8.69%. Browse 116 market data Tables ...
(Date:11/21/2014)... , Nov. 20, 2014   Atmel® Corporation ... microcontroller (MCU) and touch technology solutions, today launched the ... with the widest V cc range from ... accuracy and faster I 2 C bus communication speeds, ... EEPROM memory making them ideal for consumer, industrial, computer, ...
Breaking Biology News(10 mins):Tute Genomics Raises $2.3 Million to Scale Up Cloud-Based Genome Analytics and Accelerate Personalized Medicine 2Tute Genomics Raises $2.3 Million to Scale Up Cloud-Based Genome Analytics and Accelerate Personalized Medicine 3Industrial Security Systems Market Worth $38 Billion by 2020 2Industrial Security Systems Market Worth $38 Billion by 2020 3Atmel Launches Industry's First Wide-V(cc) Low-Power Temperature Sensor Family 2Atmel Launches Industry's First Wide-V(cc) Low-Power Temperature Sensor Family 3Atmel Launches Industry's First Wide-V(cc) Low-Power Temperature Sensor Family 4
... Sandia National Laboratories Truman Fellow Anne Ruffing has engineered ... a precursor to liquid fuels, but she has also ... Micro-algal fuels might be one way to ... would be renewable since they are powered by sunlight. ...
... changed diabetes from a death sentence to a chronic ... Case Western Reserve University School of Medicine announced a ... lives of people managing diabetes. After decades of ... international group of scientists finally found a definitive answer: ...
... can give synthetic materials the ability to "act alive" ... have found. In a paper published in ... of the National Academy of Sciences , the Pitt ... itself through a combination of chemical communication and interaction ...
Cached Biology News:Engineering alternative fuel with cyanobacteria 2Engineering alternative fuel with cyanobacteria 3After decades of research, scientists unlock how insulin interacts with cells 2After decades of research, scientists unlock how insulin interacts with cells 3Oscillating gel gives synthetic materials the ability to 'speak' 2
Other biology definitionOther Tags