Which of the following statements are correct?
Meiosis requires just one cycle of DNA replication but two successive rounds of nuclear and cell division called meiosis I and meiosis II.
After the paternal chromosomes have duplicated to form identical sister chromatids at the M phase, meiosis I begins.
At the conclusion of meiosis I, four haploid cells are produced.
In the life cycle of sexually reproducing organisms, fertilisation guarantees the creation of the haploid phase, whereas meiosis restores the diploid phase.
Statement A is true because the cell goes through two sequential cycles of nuclear and cell division to generate four haploid daughter cells, while DNA replication only happens once during meiosis. Hence option A is correct.
Statement B is untrue because sister chromatid formation does not start with the duplication of the paternal chromosomes. As opposed to that, it starts with the pairing and crossing over of homologous chromosomes, which takes place in the prophase I stage. Following this, homologous chromosomes are separated during the first meiotic division (meiosis I), which creates two haploid daughter cells. The sister chromatids are subsequently split apart during meiosis II, producing four haploid daughter cells.
Statement C is untrue due to the fact that meiosis I only generates two haploid daughter cells, not four. The production of four haploid daughter cells occurs during meiosis II.
Statement D is untrue because the production of the diploid phase, not the haploid phase, is guaranteed by fertilisation throughout the life cycle of sexually reproducing organisms. To create a zygote, which is diploid because it has all of the chromosomes from both parents, haploid gametes (sperm and egg) must undergo fertilisation. After then, the zygote divides by mitosis to become a multicellular creature. On the other hand, in sexually reproducing species, meiosis is the mechanism that brings back the haploid phase. It takes place in the testes and ovaries and results in haploid gametes (egg and sperm) that have half as many chromosomes as diploid cells. The haploid gametes combine during fertilisation to create a diploid zygote, which later grows into a multicellular creature.
Option 1 is the correct answer.