Bottlenecks, Finite Populations, and Inbreeding

• Published in: Evolutionary Quantitative Genetics pp. 285 - 338
• Main Author: Roff, Derek A
• Format: Book Chapter
• Language: English
• Published: United States Springer 1997; Springer US
• Subjects: Additive Genetic Variance; Effective Population Size; Finite Population; Inbreeding Depression; Wing Length
• ISBN: 9780412129711; 041212971X
• DOI: 10.1007/978-1-4615-4080-9_8

Although not explicitly stated, an assumption made throughout most of the analyses of the foregoing CHAPTERs is that population size, N, is an appropriate index of the number of individuals making a genetic contribution to the next generation. Specifically, it has typically been implicitly assumed that mating is at random, family size follows a Poisson distribution, N is constant, and the sex ratio is 1:1. Perhaps more significantly, it has generally been assumed that population size is sufficiently large that effects due to sampling variation can be ignored. In nature there will be many circumstances in which one or more of the preceding assumptions are violated. The consequences of such violations is the subject of this CHAPTER. Three important issues are dealt with: (1) Effective population size. Analysis of the relationship between the census population size (the total number of organisms counted in the population) and the effective population size, which is the population size that is relevant for the discussion and analysis of genetic changes in a population. (2) Effect of a finite population size on genetic variance. This analysis is divided into two components: first, the consequences of a population passing through a single generation in which population size is restricted and, second, the effect of a population being maintained over many generations at a finite size. (3) Inbreeding. One consequence of a finite population size is that mating may occur between close relatives, a phenomenon that can also occur in a very large or infinite population due to characteristics of the life history of the organism. Inbreeding frequently leads to inbreeding depression, the subject of the third section of this CHAPTER. Also considered is the converse of inbreeding depression, outbreeding depression, a phenomenon for which there is much less clear evidence of its general occurrence.