Groupes abstraits by De Seguir J.-A.

By De Seguir J.-A.

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Later in the chapter the relationship between genetic diversity and fitness will be discussed. In that context the issues of inbreeding depression and heterosis will be covered. 1 Inbreeding within populations In understanding the processes that affect allele frequencies in natural populations and thus population structure, it is useful to start with the concept of an ‘ideal population’ (Wright 1931, 1938). An ideal population is a theoretical concept defined by Wright as ‘the number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration’.

The following example is from my own research group’s work on the black grouse Tetrao tetrix in populations in western Europe. The black grouse is a sedentary bird species adapted to the ecotone between open myre/moorland within taiga forest habitats. It has a breeding range from Britain in the west to the borders of China and Korea in the east. Not much is known about population trends in the east but the species has been carefully monitored in the western part of its range. Here, there has been a general decline in population size, range contraction, and fragmentation of habitats during the last 100 years (and perhaps longer; BirdLife International 2004).

As already noted in Chapter 1 and above, the population size that matters in conservation genetic studies is not 48 Inbreeding, geographic subdivision, and gene flow always the census population size. Instead it is the number of individuals which actually reproduce and propagate their genetic material to future generations that is the determining factor for future genetic variation. Therefore geneticists are concerned with the effective population size, Ne. Theoretically this is defined as the population size that is expected given the observed allele frequencies assuming a randomly mating population.

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