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  1. Vol. 39 No. 5, p. 1282-1294
     
    Received: May 12, 1998
    Published: Sept, 1999


    * Corresponding author(s): jcrossa@cimmyt.mx
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doi:10.2135/cropsci1999.3951282x

Variance Effective Population Size under Mixed Self and Random Mating with Applications to Genetic Conservation of Species

  1. Roland Vencovskya and
  2. José Crossa *b
  1. a Dep. Genetica, ESALQ-Univ. Sao Paulo, Cx.P. 83, 13.400-970, Piracicaba, SP, Brazil
    b Biometrics and Statistics Unit, International Maize and Wheat Improvement Center (CIMMYT), Lisboa 27, Apdo. Postal 6-641, 06600 Mexico, D.F., Mexico

Abstract

When collecting and regenerating genetic resources, genetic drift affects the representation of a population and occurs at two stages: when sampling the parents and when gametes are sampled from these parents. The variance effective population size [Ne ( v )] quantifies genetic drift. In this study, a model for calculating Ne ( v ), that considers the two-stage sampling of mixed self and random mating species, is developed. For germplasm collection, as the rate of natural or artificial self-fertilization (s) increases, Ne ( v ) is reduced and becomes increasingly dependent on the number of seed parents (P) and is less influenced by the number of seeds sampled per parent (n/P). Female gametic control (GC) leads to higher Ne ( v ) than with random sampling of seeds (RS), but its effect is tangible only when n/P is small. For accession regeneration, maintaining accession integrity (the proportion of functional parents, u) at an adequately high level and adopting GC are required for assuring Ne ( v ) equal to or greater than the actual size of the accession (Ne ( v )n). The importance of these two factors is enhanced as s increases. For arbitrary rates of selfing (0 ≤ s ≤ 1), under inbreeding equilibrium (IE) and with constant population size (n = N), Ne ( v ) can be adequately maintained through GC with a loss of ≤20% within accessions. For large sample size (n → ∞), an accession loss of ≤33% can be recovered. For maintaining adequate Ne ( v ), artificial selfing followed by GC is more efficient than accession regeneration by natural reproduction. For achieving appropriate Ne ( v )s, increasing the rate of self-fertilization in polymorphic materials makes collection more difficult but regeneration easier for minimal loss (≤20%) within accessions.

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Copyright © 1999. Crop Science Society of AmericaCrop Science Society of America