uu.seUppsala University Publications
Change search
ReferencesLink to record
Permanent link

Direct link
Mutational interference and the progression of Muller's ratchet when mutations have a broad range of deleterious effects
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Molecular Evolution.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Molecular Evolution.
2007 (English)In: Genetics, ISSN 0016-6731, E-ISSN 1943-2631, Vol. 177, no 2, 971-986 p.Article in journal (Refereed) Published
Abstract [en]

Deleterious mutations can accumulate in asexual haploid genomes through the process known as Muller's ratchet. This process has been described in the literature mostly for the case where all mutations are assumed to have the same effect on fitness. In the more realistic situation, deleterious mutations will affect fitness with a wide range of effects, from almost neutral to lethal. To elucidate the behavior of the ratchet in this more realistic case, simulations were carried out in a number of models, one where all mutations have the same effect on selection [one-dimensional (1D) model], one where the deleterious mutations can be divided into two groups with different selective effects [two-dimensional (2D) model], and finally one where the deleterious effects are distributed. The behavior of these models suggests that deleterious mutations can be classified into three different categories, such that the behavior of each can be described in a straightforward way. This makes it possible to predict the ratchet rate for an arbitrary distribution of fitness effects using the results for the well-studied 1D model with a single selection coefficient. The description was tested and shown to work well in simulations where selection coefficients are derived from an exponential distribution.

Place, publisher, year, edition, pages
2007. Vol. 177, no 2, 971-986 p.
National Category
Biological Sciences
URN: urn:nbn:se:uu:diva-14378DOI: 10.1534/genetics.107.073791ISI: 000250657800027PubMedID: 17720933OAI: oai:DiVA.org:uu-14378DiVA: diva2:42148
Available from: 2008-01-30 Created: 2008-01-30 Last updated: 2011-11-03Bibliographically approved
In thesis
1. Surviving the ratchet: Modelling deleterious mutations in asexual populations
Open this publication in new window or tab >>Surviving the ratchet: Modelling deleterious mutations in asexual populations
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the most unforgiving processes in nature is that of Muller's ratchet, a seemingly irreversible accumulation of deleterious mutations that all organisms have to deal with or face extinction. The most obvious way to avoid fitness collapse is recombination, though asexual populations usually do not have the luxury of recombining freely.  With the aid of computational and mathematical models, we have studied other situations where this threat is averted and the organism can survive the ratchet.

The results show that a ratchet where all mutations have the same deleterious fitness effect is very effectively stalled for large effects. However, if mutations are allowed to have a broad range of effects, the fitness-loss rate can be substantial even with the same mean effect as the one-type ratchet, but we have  identified parameter regions where even the broad-range effects are effectively stopped.

The fitness-loss from a ratchet is very sensitive to the mutation rate and a mutation that increases the mutation rate (mutator) can easily start an otherwise stalled ratchet. Large effect mutators are heavily counter-selected, but smaller mutators can spread in the population. They can be stopped by reversals (antimutators), but even if the mutation rate is equilibrated in this way, there will be large fluctuations in mutation rate and even larger in the fitness-loss rate due to the feedback amplification in their coupling.   

Another way of preventing the ratchet is by reversal of the deleterious mutations themselves through back-mutations or compensatory mutations. The rate required to stop the ratchet using only back-mutations before the fitness collapses is very large. A detailed comparison between the deleterious mutations in the ratchet and in a sexual population was made and the difference was found to be greatest for large populations with large genomes.

There are obviously many ways to survive the ratchet, but even more ways to drive a species to extinction by enhancing and speeding up the ratchet. By modelling and testing the ratchet for numerous different situations, we show the effects of some of these threats and benefits.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 38 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 846
Theoretical biology, Population genetics, Stochastic modelling, Genome evolution, Muller's Ratchet
National Category
Genetics Microbiology Biological Sciences
Research subject
Biology with specialization in Molecular Evolution
urn:nbn:se:uu:diva-157897 (URN)978-91-554-8137-7 (ISBN)
Public defence
2011-10-07, Ekmansalen, Evolutionsbiologiskt centrum, EBC Norbyvägen 14, Uppsala, 13:00 (English)
Available from: 2011-09-15 Created: 2011-08-26 Last updated: 2011-11-03Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textPubMed

Search in DiVA

By author/editor
Söderberg, JonasBerg, Otto
By organisation
Molecular Evolution
In the same journal
Biological Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 197 hits
ReferencesLink to record
Permanent link

Direct link