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121.
Positive selection driving the evolution of a gene of male reproduction, Acp26Aa, of Drosophila: II. Divergence versus polymorphism 总被引:5,自引:1,他引:4
The evolution of the gene for a male ejaculatory protein, Acp26Aa, has been
shown to be driven by positive selection when nonsibling species in the
Drosophila melanogaster subgroup are compared. To know if selection has
been operating in the recent past and to understand the details of its
dynamics, we obtained DNA sequences of Acp26Aa and the nearby Acp26Ab gene
from 39 D. melanogaster chromosomes. Together with the 10 published
sequences, we analyzed 49 sequences from five populations in four
continents. The southern African population is somewhat differentiated from
all other populations, but its nucleotide diversity is lower at these two
loci. We find the following results for Acp26Aa: (1) The R: S (replacement
: silent changes) ratio is significantly higher in the between-species
comparisons than in the within-species data by the McDonald and Kreitman
test. Positive selection is probably responsible for the excess of amino
acid replacements between species. (2) However, within-species nucleotide
diversity is high. Neither the Tajima test nor the Fu and Li test indicates
a reduction in nucleotide diversity due to positive selection in the recent
past. (3) The newly derived nucleotides in D. melanogaster are at high
frequency significantly more often than predicted by the neutral
equilibrium. Since the nearby Acp26Ab gene does not show these patterns,
these observations cannot be attributed to the characteristics of this
chromosomal region. We suggest that positive selection is active, but may
be weak, for each amino acid change in the Acp26Aa gene.
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