These results suggest that in addition to the mean admixture, other easily measured quantities such as the variance and higher moments of the admixture fraction are likely to be informative, together with the mean, in statistical procedures for estimating the parameters of the historical admixture model that gives rise to a hybrid population.
We show that very different admixture processes can produce identical mean admixture proportions, but that such processes produce different values for the variance of the admixture proportion.
To determine whether and how admixture affects genetic diversity, we ran a linear regression analysis between the mean allelic richness AR and the mean admixture proportion of populations.
For admixture on the autosomes, the mean admixture is constant after the founding of the admixed population, and for the X chromosome, the mean X-chromosomal admixture approaches a limit rather than remaining constant in time.
If, instead, we could only detect 0.5% mean admixture in the present-day population, we have ∼0 power to detect 5% ancient admixture and ∼35% power to detect 10% ancient admixture (Fig. 2C).
We have found that because of model dependence, time dependence, and a lack of identifiability of admixture parameters from mean admixture alone, a variety of admixture processes and parameter values might be compatible with estimates of the mean admixture on X chromosomes and the autosomes.
For recent admixture in the single-admixture model, or in a model with continuing admixture after the founding of the admixed population, the mean admixture fractions from S 1 for the X chromosome depend on the sex-specific contributions in a more complex way, incorporating the sex-specific contributions from S 2 (Equations 12, 13, and 17 20).
Thus, Equation 35 predicts that the distribution of the admixture fraction for a random individual in the hybrid population contracts around the mean, converging to a constant equal to the mean admixture from the first generation.
Mean admixture from BOU was estimated at 0.090 ± 0.151 in BER, and 0.020 ± 0.038 in MET (Table 1).
Mean admixture coefficients were computed for each population in the database (see Elhaik et al. [ 21] for details).
