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Figure 3 | BMC Genetics

Figure 3

From: A single mutation results in diploid gamete formation and parthenogenesis in a Drosophila yemanuclein-alpha meiosis I defective mutant

Figure 3

yem1 chromosomes bypass the meiotic arrest in a recombination defective background but fail to undergo the two divisions within the oocyte. A - Schematic representation of meiosis progression in stage 14 oocytes. In a wild type oocyte, the meiotic cycle pauses at metaphase I as a result of the tension generated between chiasmata and kinetochores. Meiosis resumption is triggered by ovulation. Recombination defective mutants (mut-rec) do not experience metaphase I arrest in the oocyte; their chromosomes undergo precocious anaphase as does achiasmate 4th chromosome. (B, C) Gallery of pictures showing oocytes with various recombination defective genotypes stained for DNA (DAPI) and the spindle (anti alpha-tubulin antibody). (B) Precocious anaphase (left) and anaphase II (right) spindles in mei-2181 oocytes. (C) Prometaphase and metaphase I yem1/Df3450 oocytes (upper panel). Precocious anaphase I and exceptional anaphase II (arrow) in mei-W681; yem1/Df3450 and mei-9a; yem1/Df3450 oocytes (lower panel). Note that the mutant chromosomes are not equally partitioned on the spindle. The last picture (*) shows a highly elongated double mutant spindle. Scale: the bar represents 5 μm. D - Histogram representing the ratio of the 3 classes of meiotic figures scored for 4 different genotypes. (n) Represents total number of oocytes scored for each genotype. The 3 meiotic classes considered here are: prometaphase, metaphase I (light purple), anaphase I (white) and meiosis II (dark purple). In a mut-rec background (here mei-W681 and mei-9a), yem1 mutants bypass the metaphase I arrest. In contrast to simple recombination defective mutants (mut-rec), meiosis II spindles are hardly observed in mut-rec; yem1/Df3450 oocytes. Obviously these mutant chromosomes were not able to support the two meiotic divisions within the oocyte. Abbreviations: PMI (prometaphase I); MI (metaphase I); AI (anaphase I); MII (metaphase II); AII (anaphase II).

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