Affiliation:
1. Department of Evolutionary Biology, Uppsala University, Uppsala 752 36, Sweden
Abstract
ABSTRACT
The origin and early evolution of sex chromosomes are currently poorly understood. The
Neurospora tetrasperma
mating-type (
mat
) chromosomes have recently emerged as a model system for the study of early sex chromosome evolution, since they contain a young (<6 million years ago [Mya]), large (>6.6-Mb) region of suppressed recombination. Here we examined preferred-codon usage in 290 genes (121,831 codon positions) in order to test for early signs of genomic degeneration in
N. tetrasperma
mat
chromosomes. We report several key findings about codon usage in the region of recombination suppression, including the following: (i) this region has been subjected to marked and largely independent degeneration among gene alleles; (ii) the level of degeneration is magnified over longer periods of recombination suppression; and (iii) both
mat a
and
mat A
chromosomes have been subjected to deterioration. The frequency of shifts from preferred codons to nonpreferred codons is greater for shorter genes than for longer genes, suggesting that short genes play an especially significant role in early sex chromosome evolution. Furthermore, we show that these degenerative changes in codon usage are best explained by altered selection efficiency in the recombinationally suppressed region. These findings demonstrate that the fungus
N. tetrasperma
provides an effective system for the study of degenerative genomic changes in young regions of recombination suppression in sex-regulating chromosomes.
Publisher
American Society for Microbiology
Subject
Molecular Biology,General Medicine,Microbiology
Cited by
36 articles.
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