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Intron size and exon evolution in Drosophila - PubMed

Intron size and exon evolution in Drosophila

Gabriel Marais et al. Genetics. 2005 May.

Abstract

We have found a negative correlation between evolutionary rate at the protein level (as measured by d(N)) and intron size in Drosophila. Although such a relation is expected if introns reduce Hill-Robertson interference within genes, it seems more likely to be explained by the higher abundance of cis-regulatory elements in introns (especially first introns) in genes under strong selective constraints.

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Figures

F<sc>igure</sc> 1.—
Figure 1.—

The relationship between intron size and rate of nonsynonymous substitutions per site (dN) in D. melanogaster. (A) dN is 1.6 times lower in genes with introns than in genes without introns (a nonparametric Kolmogorov, P = 0.02). As in the rest of the article, we used nonparametric statistics because most of the variables with which we are dealing do not follow the normal distribution. Error bars are 95% confidence intervals. (B) dN is negatively correlated with total intron size (Spearman nonparametric correlation coefficient Rs = −0.19, P < 10−4). (C) dN for different intron size categories (each category contains ∼20% of the genes). Error bars are 95% confidence intervals.

F<sc>igure</sc> 2.—
Figure 2.—

The relationship between intron size and expression level (estimated by EST counting) for the complete genome of D. melanogaster (data set from M

arais

and P

iganeau

2002). For first introns, Rs = 0.06, P < 10−4. For other introns, Rs = −0.03, NS. Only introns located in regions of high recombination were included (the total number of these introns is shown). Error bars are 95% confidence intervals.

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