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Unlike some organisms, horses and donkeys can't reproduce asexually. So the mule cannot reproduce because its chromosomes cannot properly pair up during meiosis, the critical step in sexual reproduction.
In this activity, we learned that in asexual reproduction, organisms create genetically identical copies of themselves. We discussed four types of asexual reproduction: parthenogenesis, binary fission, budding, and fragmentation with regeneration.
Sexual reproduction produces new combinations of genes. The sexual life cycle includes an alternation between haploid and diploid cells. Fertilization and meiosis are the hallmarks of the sexual life cycle. Meiosis consists of two rounds of cell division, meiosis I and meiosis II. The stages of meiosis I and II have similar names to those of mitosis, and are sometimes separated by interkinesis. The purpose of meiosis is to reduce the number of chromosomes in a diploid cell from 2n to 1n, and to produce genetic diversity. Genetic diversity is produced during crossing over during prophase I, and by independent assortment during metaphase I.
Asexual reproduction is favored in stable environments, while sexual reproduction is favored in changing environments. Some animals can switch between sexual and asexual reproduction in response to their environment.
In the Demonstration that follows, we’re going to learn how observing crossing over can help us measure the distances between genes, which is the first step in gene mapping.
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