Meiosis160-page3

Meiosis160-page3 - Although we are familiar with and...

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Meiosis and Life Cycles - 3 The offspring (children) formed by sexual reproduction will have genetic variation, important for the long-term response of species to their environment. Such variations among offspring lead to physical, behavioral and physiological differences. These differences may be more or less useful in the surroundings of that organism, and are subject to the agents of selection. This variation is an important basis for evolutionary change, which will be discussed later. Meiosis and the Life Cycles of Organisms Meiosis is something that takes place at just one point in any sexually reproducing organism's life cycle. In animals, meiosis generally occurs to form gametes: sperm or eggs. In many other types of organisms, meiosis occurs at some different point in the life cycle, and the products of meiosis may be spores, (as in plants) or the first cells of the next generation (for most protists and most fungi). At some point however, all organisms that sexually reproduce will make haploid gametes.
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Unformatted text preview: Although we are familiar with, and comfortable with the animal life cycle, it's good to know how different organisms fit meiosis into their life cycles. Similarly, fertilization occurs at one point in an organism's life history. Fertilization occurs between two different haploid cells, called gametes, to form the zygote, or fertilized egg. The zygote obtains half its chromosomes from the sperm and half from the egg or from different gametes, the more general term. Fusion of gametes restores the diploid number, and in so doing, also restores homologous chromosomes (one of each kind being provided by the sperm and one of each kind coming from the egg). Since each gamete has a unique combination of chromosomes, each zygote will be unique, and genetic variation is both maintained and obtained within the species. We will now discuss typical life cycle patterns and look at the timing of meiosis in the life cycle....
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