Skip to main content
    • Aa
    • Aa

Mutation accumulation in finite outbreeding and inbreeding populations

  • D. Charlesworth (a1), M. T. Morgan (a1) and B. Charlesworth (a1)

We have carried out an investigation of the effects of various parameters on the accumulation of deleterious mutant alleles in finite diploid populations. Two different processes contribute to mutation accumulation. In random-mating populations of very small size and with tight linkage, fixation of mutant alleles occurs at a high rate, but decreases with extremely tight linkage. With very restricted recombination, the numbers of low-frequency mutant alleles per genome in randommating populations increase over time independently of fixation (Muller's ratchet). Increased population size affects the ratchet less than the fixation process, and the decline in population fitness is dominated by the ratchet in populations of size greater than about 100, especially with high mutation rates. The effects of differences in the selection parameters (strength of selection, dominance coefficient), of multiplicative versus synergistic selection, and of different amounts of inbreeding, are complex, but can be interpreted in terms of opposing effects of selection on individual loci and associations between loci. Stronger selection slows the accumulation of mutations, though a faster decline in mean fitness sometimes results. Increasing dominance tends to have a similar effect to greater strength of selection. High inbreeding slows the ratchet, because the increased homozygous expression of mutant alleles in inbred populations has effects similar to stronger selection, and because with inbreeding there is a higher initial frequency of the least loaded class. Fixation of deleterious mutations is accelerated in highly inbred populations. Even with inbreeding, sexual populations larger than 100 will probably rarely experience mutation accumulation to the point that their survival is endangered because neither fixation nor the ratchet has effects of the magnitude seen in asexual populations. The effects of breeding system and rate of recombination on the rate of molecular evolution by the fixation of slightly deleterious alleles are discussed.

Corresponding author
* Corresponding author.
Linked references
Hide All

This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

K. C Attwood , L. K. Schneider & F. J. Ryan (1951). Selective mechanisms in bacteria. Cold Spring Harbor Symposium on Quantitative Biology 16, 345355.

J. C Avise , J. C Trexler , J. Travis & W. S. Nelson (1991). Poecilia mexicana is the female parent of the unisexual fish. P. formosa. Evolution 45, 15301533.

G. Bell (1988). Recombination and the immortality of the germ line. Journal of Evolutionary Biology 1, 6782.

C. W. Birky & J. B. Walsh (1988). Effects of linkage on rates of molecular evolution. Proceedings of the National Academy of Sciences of the USA 85, 64146418.

L. Chao , T. Tran & C. Matthews (1992). Muller's ratchet and the advantage of sex in the RNA virus f6. Evolution 46, 289299.

B. Charlesworth (1978). A model for the evolution of Y chromosomes and dosage compensation. Proceedings of the National Academy of Sciences of the USA 75, 56185622.

B. Charlesworth (1992). Evolutionary rates in partially selffertilizing species. American Naturalist 140, 126148.

D. Charlesworth , M. T. Morgan & B. Charlesworth (1990). Inbreeding depression, genetic load and the evolution of outcrossing rates in a multi-locus system with no linkage. Evolution 44, 14691489.

J. F. Crow (1970). Genetic loads and the cost of natural selection. In Mathematical Models in Population Genetics (ed. K.-I. Kojima ), pp. 128177. Berlin: Springer-Verlag.

J. Haigh (1978). The accumulation of deleterious genes in a population. Theoretical Population Biology 14, 251267.

J. B. S. Haldane (1950). The association of characters as a result of inbreeding and linkage. Annals of Eugenics 15, 1523.

D. Houle , D. K. Hoffmaster , S. Assimacopoulos , and B. Charlesworth (1992). The genomic rate of mutation for fitness in Drosophila. Nature 359, 5860.

W.-H Li . (1987). Models of nearly neutral mutations with particular implications for nonrandom usage of synonymous codons. Journal of Molecular Evolution 24, 337345.

M. Lynch & W. Gabriel (1990). Mutation load and the survival of small population. Evolution 44, 17251737.

J. T. Manning (1983). The consequences of mutation in multi-clonal asexual species. Heredity 50, 1519.

A. L. Melzer & J. H. Koeslag (1991). Mutations do not accumulate in asexual isolates capable of growth and extinction: Muller's ratchet re-examined. Evolution 45, 649655.

H. J. Muller (1964). The relation of recombination to mutational advance. Mutation Research 1, 29.

M. Nei (1970). Accumulation of nonfunctional genes on sheltered chromosomes. American Naturalist 104, 311322.

T. Ohta (1976). Role of very slightly deleterious mutations in molecular evolution and polymorphism. Theoretical Population Biology 10, 254275.

J. M. Quattro , J. C. Avise & R. C. Vrijenhoek (1992). An ancient clonal lineage in the fish Poeciliopsis (Atheriniformes: Poeciliidae). Proceedings of the National Academy of Sciences of the USA 89, 348352.

R. C Vrijenhoek , R. A. Angus & R. J. Schultz (1977). Variation and heterozygosity in sexually versus clonally reproducing populations of Poeciliopsis. Evolution 31, 767781.

R. C. Vrijenhoek (1979). Factors affecting clonal diversity and coexistence. American Zoologist 19, 787797.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Genetics Research
  • ISSN: 0016-6723
  • EISSN: 1469-5073
  • URL: /core/journals/genetics-research
Please enter your name
Please enter a valid email address
Who would you like to send this to? *


Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 29 *
Loading metrics...

Abstract views

Total abstract views: 165 *
Loading metrics...

* Views captured on Cambridge Core between September 2016 - 29th May 2017. This data will be updated every 24 hours.