In sexual reproduction in ciliates the sequence of events is
A. (1) In each conjugating cell, the macronucleus and micronucleus undergo meiosis. One haploid macronucleus and micronucleus disintegrate in each cell.
(2) The remaining nuclei undergo mitosis to produce two macronuclei and two micronuclei.
(3) One set of nuclei stays in the parent cell and the other moves to the opposite cell.
(4) The cells separate, each with two sets of nuclei, one of its own and one from its conjugant.
(5) The two haploid micronuclei in each cell fuse to form a diploid micronucleus, and the two macronuclei fuse to form a diploid macronucleus.
(6) The diploid nuclei mitotically, producing four diploid macronuclei and four micronuclei.
B. (1) In each conjugating cell, the micronucleus undergoes meiosis to produce four haploid micronuclei, of which three disintegrate.
(2) The remaining micronucleus undergoes mitosis to produce two.
(3) One micronucleus stays in the parent cell and the other moves to the opposite cell while the macronucleus in each cell disintegrates.
(4) The cells separate, each with two nuclei, one of its own and one from its conjugant.
(5) The two haploid micronuclei in each cell fuse to form a diploid micronucleus.
(6) The diploid micronucleus divides mitotically, producing four diploid macronuclei and four micronuclei.
C. (1) In the pair of conjugating cells, the micronuclei undergo mitosis to produce four diploid micronuclei. All but one of these micronuclei disintegrate.
(2) The remaining micronucleus undergoes meiosis to produce two.
(3) One micronucleus stays in the parent cell and the other moves to the opposite cell while the macronucleus in each cell disintegrates.
(4) The cells separate, each with two nuclei.
(5) One haploid micronucleus in each cell forms a new haploid macronucleus and the other divides mitotically to form eight new haploid micronuclei.
(6) The two haploid macronuclei fuse to form a diploid one and the eight haploid micronuclei fuse by pairs into four diploid micronuclei.
Answer: B
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