053 CLONAL DECLINE IN HORTICULTURAL CROPS DUE TO MULLER'S RATCHET

It should be possible to maintain horticultural clones unchanged forever through asexual generations, as commercial propagators and clonal repositories maintain clonal integrity, disease-free stock plants, or remove mutations. However, unintentional selection for nonhorticultural traits could still be occurring. Accumulations of such traits would be due to the operation of Muller's ratchet and include fertility losses, increases in virus titer, and stunted growth habit. In chrysanthemums, Dendranthema grandiflora. clones separated from sexual cycles for generations become increasingly sterile. Seed set across years, using coefficients of crossability (FCC/MCC), was examined for garden clones (forced through sexual cycles annually) and greenhouse clones (asexual cycles only). Garden clones 40 years old (54-101-11) had only depressed levels of fertility. In other cases (77-AM 3-17), the ratchet was reversed >1 sexual cycle. Greenhouse clones were often completely sterile since their propagation is primarily asexual.

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Genetic Hitchhiking and the Evolution of Reduced Genetic Activity of the Y Sex Chromosome

Genetics ◽

10.1093/genetics/116.1.161 ◽

1987 ◽

Vol 116 (1) ◽

pp. 161-167

Author(s):

William R Rice

Keyword(s):

Y Chromosome ◽

Alternative Model ◽

Sex Chromosome ◽

Deleterious Mutations ◽

Genetic Hitchhiking ◽

New Model ◽

Muller's Ratchet ◽

Genetic Activity ◽

Muller’S Ratchet ◽

Selection For

ABSTRACT A new model for the evolution of reduced genetic activity of the Y sex chromosome is described. The model is based on the process of genetic hitchhiking. It is shown that the Y chromosome can gradually lose its genetic activity due to the fixation of deleterious mutations that are linked with other beneficial genes. Fixation of deleterious Y-linked mutations generates locus-specific selection for dosage tolerance and/or compensation. The hitchhiking effect is most pronounced when operating in combination with an alternative model, Muller's ratchet. It is shown, however, that the genetic hitchhiking mechanism can operate under conditions where Muller's ratchet is ineffective.

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Sex, fitness decline and recombination – Muller’s ratchet vs. Ohta’s ratchet

10.1101/2020.08.06.240713 ◽

2020 ◽

Author(s):

Yongsen Ruan ◽

Haiyu Wang ◽

Lingjie Zhang ◽

Haijun Wen ◽

Chung-I Wu

Keyword(s):

Parameter Space ◽

Asexual Population ◽

Main Hypothesis ◽

Muller's Ratchet ◽

Restricted Parameter Space ◽

Biological Phenomena ◽

Muller’S Ratchet ◽

Selection For ◽

Driving Fitness ◽

Special Case

AbstractIt is generally accepted that the absence of recombination reduces the efficacy of natural selection for, or against, mutations. A special case is Muller’s Ratchet (MR) whereby non-recombining genomes experience irreversible fitness decline due to the accumulation of deleterious mutations. MR has been a main hypothesis for sexual reproduction as well as many other biological phenomena. We now ask whether the fitness decline can indeed be stopped if an asexual population turns sexual to become recombining. The possible fitness decline under recombination is referred to as Ohta’s Ratchet (OR). In comparison, MR is more effective in driving fitness reduction than OR, but only in a restricted parameter space of mutation rate, population size and selection. Outside of this space, the two ratchets are equally effective or, alternatively, neither is sufficiently powerful. Furthermore, beneficial mutations can affect the population fitness, which may diverge between the two ratchets, but only in a small parameter space. Since recombination plays a limited role in driving fitness decline, the operation of MR could be far less common in nature than believed. A companion report (see Supplement) surveying the biological phenomena attributed to MR indeed suggests the alternative explanations to be generally more compelling.

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The accumulation of deleterious genes in a population—Muller's Ratchet

Theoretical Population Biology ◽

10.1016/0040-5809(78)90027-8 ◽

1978 ◽

Vol 14 (2) ◽

pp. 251-267 ◽

Cited By ~ 302

Author(s):

John Haigh

Keyword(s):

Muller's Ratchet ◽

Muller’S Ratchet ◽

Deleterious Genes

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CORRELATED RESPONSE IN BROWN SARSON

Canadian Journal of Genetics and Cytology ◽

10.1139/g70-114 ◽

1970 ◽

Vol 12 (4) ◽

pp. 905-913 ◽

Cited By ~ 1

Author(s):

T. Swamy Rao

Keyword(s):

Gamma Irradiation ◽

Seed Set ◽

Previous History ◽

The Self ◽

Correlated Response ◽

History Of ◽

Self Compatibility ◽

Selection For ◽

Direction Opposite ◽

Brown Sarson

The correlated response with changes in self-compatibility in three varieties of brown sarson subjected to gamma irradiation was examined. Selection for improved seed set in the irradiated populations showed that substantial correlated response can result for a constellation of other characters in which the self-compatible and self-incompatible forms differ. The correlated response was in a direction opposite to that of the previous history of selection.

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Muller’s ratchet of the Y chromosome with gene conversion

Genetics ◽

10.1093/genetics/iyab204 ◽

2021 ◽

Author(s):

Takahiro Sakamoto ◽

Hideki Innan

Keyword(s):

Gene Duplication ◽

Gene Conversion ◽

Y Chromosome ◽

Conversion Rate ◽

Single Copy ◽

Duplicated Genes ◽

Fitness Effect ◽

Muller's Ratchet ◽

Y Chromosomes ◽

Muller’S Ratchet

Abstract Muller’s ratchet is a process in which deleterious mutations are fixed irreversibly in the absence of recombination. The degeneration of the Y chromosome, and the gradual loss of its genes, can be explained by Muller’s ratchet. However, most theories consider single-copy genes, and may not be applicable to Y chromosomes, which have a number of duplicated genes in many species, which are probably undergoing concerted evolution by gene conversion. We developed a model of Muller’s ratchet to explore the evolution of the Y chromosome. The model assumes a non-recombining chromosome with both single-copy and duplicated genes. We used analytical and simulation approaches to obtain the rate of gene loss in this model, with special attention to the role of gene conversion. Homogenization by gene conversion makes both duplicated copies either mutated or intact. The former promotes the ratchet, and the latter retards, and we ask which of these counteracting forces dominates under which conditions. We found that the effect of gene conversion is complex, and depends upon the fitness effect of gene duplication. When duplication has no effect on fitness, gene conversion accelerates the ratchet of both single-copy and duplicated genes. If duplication has an additive fitness effect, the ratchet of single-copy genes is accelerated by gene duplication, regardless of the gene conversion rate, whereas gene conversion slows the degeneration of duplicated genes. Our results suggest that the evolution of the Y chromosome involves several parameters, including the fitness effect of gene duplication by increasing dosage and gene conversion rate.

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Muller's Ratchet

Encyclopedia of Genetics, Genomics, Proteomics and Informatics ◽

10.1007/978-1-4020-6754-9_10903 ◽

2008 ◽

pp. 1283-1284

Keyword(s):

Muller's Ratchet ◽

Muller’S Ratchet

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SELECTION FOR SEED SET IN NONINBRED AND PARTLY INBRED POPULATIONS OF ALFALFA

Canadian Journal of Plant Science ◽

10.4141/cjps77-126 ◽

1977 ◽

Vol 57 (3) ◽

pp. 873-881 ◽

Cited By ~ 2

Author(s):

R. MICHAUD ◽

T. H. BUSBICE

Keyword(s):

Medicago Sativa ◽

Seed Set ◽

Exponential Model ◽

Seed Setting ◽

Medicago Sativa L ◽

Selection For ◽

Inbred Populations ◽

The Relationship ◽

Advanced Generation ◽

Coefficient Of Inbreeding

Alfalfa (Medicago sativa L.) is a highly heterozygous cross-pollinating species, and most breeding efforts have been conducted on noninbred populations. The purpose of this study was to determine whether greater breeding progress could be made by selecting within partly inbred populations rather than within noninbred ones. One hundred and twenty F1 (noninbred) and 120 S1 (partly inbred) plants that were issued from crossing and selfing four alfalfa clones were evaluated for self-fertility. The most self-fertile 10% of the plants from each family were selected in each population. The selected plants within each level of inbreeding were intercrossed to produce an advanced generation in which the effectiveness of the selection was evaluated. Selection increased both self- and cross-fertility in the advanced generation. Selection was more effective at the F1 level than at the S1 level. Fertility was reduced drastically by inbreeding. The average self-fertility of the S1’s was only about 7% of the cross-fertility of their parental clones. An exponential model was proposed to describe the relationship between seed setting and the coefficient of inbreeding in the developing zygote. This model explained 95% of the variation among 11 unselected populations having differing levels of inbreeding.

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Amazon molly and Muller's ratchet

Nature ◽

10.1038/375111c0 ◽

1995 ◽

Vol 375 (6527) ◽

pp. 111-112 ◽

Cited By ~ 1

Author(s):

Leo W. Beukeboom ◽

Rolf P. Weinzierl ◽

Nico K. Michiels

Keyword(s):

Muller's Ratchet ◽

Amazon Molly ◽

Muller’S Ratchet

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Drastic Fitness Loss in Human Immunodeficiency Virus Type 1 upon Serial Bottleneck Events

Journal of Virology ◽

10.1128/jvi.73.4.2745-2751.1999 ◽

1999 ◽

Vol 73 (4) ◽

pp. 2745-2751 ◽

Cited By ~ 121

Author(s):

Eloisa Yuste ◽

Sonsoles Sánchez-Palomino ◽

Concha Casado ◽

Esteban Domingo ◽

Cecilio López-Galíndez

Keyword(s):

Human Immunodeficiency Virus ◽

Human Immunodeficiency Virus Type ◽

Virus Type ◽

Field Isolate ◽

Plaque Assay ◽

Muller's Ratchet ◽

Immunodeficiency Virus ◽

Muller’S Ratchet ◽

Hiv 1

ABSTRACT Muller’s ratchet predicts fitness losses in small populations of asexual organisms because of the irreversible accumulation of deleterious mutations and genetic drift. This effect should be enhanced if population bottlenecks intervene and fixation of mutations is not compensated by recombination. To study whether Muller’s ratchet could operate in a retrovirus, 10 biological clones were derived from a human immunodeficiency virus type 1 (HIV-1) field isolate by MT-4 plaque assay. Each clone was subjected to 15 plaque-to-plaque passages. Surprisingly, genetic deterioration of viral clones was very drastic, and only 4 of the 10 initial clones were able to produce viable progeny after the serial plaque transfers. Two of the initial clones stopped forming plaques at passage 7, two others stopped at passage 13, and only four of the remaining six clones yielded infectious virus. Of these four, three displayed important fitness losses. Thus, despite virions carrying two copies of genomic RNA and the system displaying frequent recombination, HIV-1 manifested a drastic fitness loss as a result of an accentuation of Muller’s ratchet effect.

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