Diploidy and Muller's ratchet

✍ Scribed by J. T. Manning

• Publisher: Springer
• Year: 1983
• Tongue: English
• Weight: 223 KB
• Volume: 32
• Category: Article
• ISSN: 0001-5342
• DOI: 10.1007/bf00048239

✦ Synopsis

Under the influence of deleterious mutation and selection a population will reach equilibrium and contain individuals with [0, 1, 2 --mutations. ] This deterministic equilibrium distribution is exactly the same for asexual and sexual populations. The size of the optimal class (no) , i.e. the class with the smallest number of mutations, is determined by the genome mutation rate (U) and the average selective disadvantage (s) of the mutations. A large U and small s gives a very small no. If n o is small in an asexual population it will be lost by drift and this causes a reduction in the mean fitness of the population (by the ratchet mechanism). It is argued that diploidy (when compared to haploidy) increases U and reduces s. Values of U and s observed from Drosophila indicate a diploid would have a vanishingly small n o. The argument suggests Muller's ratchet is more powerful than previously accepted in asexual species derived from diploid sexual ancestors.