Descritpion of a double mutant strain of Drosophila melanogaster useful for genetic laboratory courses.

Many years ago, individuals showing drastically reduced eyes arose in our laboratory e (ebony) strain (Bridges and Morgan, 1923). We selected those flies presenting both traits and constituted a new double mutant strain e su (e, ebony; su, 'sense ulls', eyes drastically reduced). Both mutations were linked and located in the chromosome III. We used this strain in linkage analyses with our undergraduate students. [...

Molecular population genetics of the Polycomb genes in Drosophila subobscura

Polycomb group (PcG) proteins are important regulatory factors that modulate the chromatin state. They form protein complexes that repress gene expression by the introduction of posttranslational histone modifications. The study of PcG proteins divergence in Drosophila revealed signals of coevolution among them and an acceleration of the nonsynonymous evolutionary rate in the lineage ancestral to the obscura group species, mainly in subunits of the Pcl-PRC2 complex. Herein, we have studied the nucleotide polymorphism of PcG genes in a natural population of D. subobscura to detect whether natural selection has also modulated the evolution of these important regulatory genes in a more recent time scale. Results show that most genes are under the action of purifying selection and present a level and pattern of polymorphism consistent with predictions of the neutral model, the exceptions being Su(z)12 and Pho. MK tests indicate an accumulation of adaptive changes in the SU(Z)12 protein during the divergence of D. subobscura and D. guanche. In contrast, the HKA test shows a deficit of polymorphism at Pho. The most likely explanation for this reduced variation is the location of this gene in the dot-like chromosome and would indicate that this chromosome also has null or very low recombination in D. subobscura, as reported in D. melanogaster

Summary of synonymous and nonsynonymous polymorphism and divergence with <i>D</i>. <i>guanche</i> in the PcG genes.

<p>Summary of synonymous and nonsynonymous polymorphism and divergence with <i>D</i>. <i>guanche</i> in the PcG genes.</p

Location of the PcG genes on the <i>D</i>. <i>subobscura</i> chromosomes.

<p>The location of the sixteen studied PcG genes is indicated on the polytene chromosomes of <i>D</i>. <i>subobscura</i> (<i>ch cu</i> strain) by arrowheads. All chromosomes have the standard arrangement shown in the cytological map of the species [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0185005#pone.0185005.ref027" target="_blank">27</a>] except the O chromosome that has the O₃₊₄ arrangement that includes the overlapping inversions O₃ and O₄. Chromosomes are identified by capital letters (A, J, U, E and O) at the distal end. The dot-like chromosome is also indicated (Dot).</p

Nucleotide diversity and divergence along <i>Pho</i> and <i>Su(z)12</i>.

<p>Sliding window plots of the distribution of nucleotide diversity in <i>D</i>. <i>subobscura</i> (<i>π</i>, black line) and of nucleotide divergence between <i>D</i>. <i>subobscura</i> and <i>D</i>. <i>guanche</i> (<i>K</i>, gray line). Windows include 50 sites with successive displacements of 5 sites. The <i>x</i>-axis indicates nucleotide sites across the gene region and the <i>y</i>-axis indicates nucleotide diversity or divergence. Solid boxes in the lower part of the figure indicate the coding exons and thin lines show flanking regions and introns. The protein domains of the encoded proteins are indicated below the gene structure with empty boxes.</p

Summary estimates of the level and pattern of polymorphism.

<p>Summary estimates of the level and pattern of polymorphism.</p

Polymorphism and divergence in the coding region of the PcG genes.

<p>Ratio of nonsynonymous to synonymous polymorphism in <i>D</i>. <i>subobscura</i> (<i>π</i>_<i>a</i>/<i>π</i>_<i>s</i>) and of nonsynonymous to synonymous divergence between <i>D</i>. <i>subobscura</i> and <i>D</i>. <i>guanche</i> (<i>K</i>_<i>a</i><i>/K</i>_<i>s</i>) for each of the Polycomb genes studied. The <i>x</i>-axis indicates gene identity and the <i>y</i>-axis indicates <i>π</i>_<i>a</i>/<i>π</i>_<i>s</i> and <i>K</i>_<i>a</i><i>/K</i>_<i>s</i> values. <i>Pho</i> lacks synonymous polymorphism and <i>Caf1-55</i> nonsynonymous polymorphism. Genes on the <i>x</i>-axis are grouped according to Polycomb complex. dRAF also contains PSC and SCE.</p

Molecular population genetics of the Polycomb genes in <i>Drosophila subobscura</i>

<div><p>Polycomb group (PcG) proteins are important regulatory factors that modulate the chromatin state. They form protein complexes that repress gene expression by the introduction of posttranslational histone modifications. The study of PcG proteins divergence in <i>Drosophila</i> revealed signals of coevolution among them and an acceleration of the nonsynonymous evolutionary rate in the lineage ancestral to the <i>obscura</i> group species, mainly in subunits of the Pcl-PRC2 complex. Herein, we have studied the nucleotide polymorphism of PcG genes in a natural population of <i>D</i>. <i>subobscura</i> to detect whether natural selection has also modulated the evolution of these important regulatory genes in a more recent time scale. Results show that most genes are under the action of purifying selection and present a level and pattern of polymorphism consistent with predictions of the neutral model, the exceptions being <i>Su(z)12</i> and <i>Pho</i>. MK tests indicate an accumulation of adaptive changes in the SU(Z)12 protein during the divergence of <i>D</i>. <i>subobscura</i> and <i>D</i>. <i>guanche</i>. In contrast, the HKA test shows a deficit of polymorphism at <i>Pho</i>. The most likely explanation for this reduced variation is the location of this gene in the dot-like chromosome and would indicate that this chromosome also has null or very low recombination in <i>D</i>. <i>subobscura</i>, as reported in <i>D</i>. <i>melanogaster</i>.</p></div

Descritpion of a double mutant strain of Drosophila melanogaster useful for genetic laboratory courses.

Many years ago, individuals showing drastically reduced eyes arose in our laboratory e (ebony) strain (Bridges and Morgan, 1923). We selected those flies presenting both traits and constituted a new double mutant strain e su (e, ebony; su, 'sense ulls', eyes drastically reduced). Both mutations were linked and located in the chromosome III. We used this strain in linkage analyses with our undergraduate students. [...