As duplicates age, both the population genetic process of failed fixation and the mutation-driven process of nonfunctionalization act to reduce the observed number of duplicates.
Although the frequency of noncycling duplicates decreased with Ks, the frequency of cycling duplicates was greater on average for Ks > 0.9 indicating a net gain of cycling expression as duplicates age.
This observation was interpreted as evidence of relaxed purifying selection immediately after duplication that was then followed by increased selective constraints as the duplicates aged.
Our results suggest that duplication age and genetic buffering determine the essentiality of mouse duplicates.
We then calculated the mean of protein interaction number for duplicated genes in each age bin and found no correlation of the mean protein connectivity with the duplication age (t) (Spearman rank ρ = 0.04, P = 0.19, Figure 4(b)).
As expected, P E * t) increases with the duplication age t, but much slower than P E -dup(t), indicating that the P E - d N / d S correlation can only explain a small portion of the P E -age correlation in duplicates.
Consistent with the duplicate gene age distributions, phylogenetic analyses of these gene families demonstrate that At-β is shared by Arabidopsis and Cleome and that At-α is restricted to the Brassicaceae (fig. 3, supplementary table S3, Supplementary Material online).
Six of them were duplicates (same age, gender, area code, etc).; and 35 were from subjects outside Créteil.
We therefore conclude that the proportion of essential genes (P E ) of mouse duplicates is age dependent, even after correcting the potential confounding effect from the essentiality-conservation dependence.
Distinguishing FSGD duplicates from other types of WGD (1R/2R) or local gene duplications is essential because duplicates of varying age and type show different patterns of duplicate retention and functional evolution (Maere et al. 2005; Aury et al. 2006; Wapinski et al. 2007).
