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14.2: Introduction

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  • If the only type of cell division eukaryotes underwent was mitosis, the only source of genetic variation we would have would be through mutations. Mutations still provide the foundation for differences, but another type of cell division allows organisms to mix and match their own DNA. In meiosis, the sets of chromosomes that an organism inherited from each parent interact and recombine to form novel combinations. The haploid cells or organisms produced through this process can then fuse with another haploid cell or organism that has gone through the same process of recombination.

    The result is that these sexually reproducing populations are composed of genetically distinct individuals. As environmental conditions change, genetically diverse populations have more options within the gene pool to adapt to those conditions. This increases the overall likelihood of survival of that species. As always, there are trade-offs to each type of reproduction.

    Asexually reproducing organisms can mass-clone themselves and often reproduce quickly, investing very little in the survival of individual clones and instead relying on the probability that some might survive. Often, these organisms are found in high-resource environments (like mold on a sugary fruit) or colonizing a new area because they do not need a partner to reproduce.

    Sexually reproducing organisms generally require a compatible partner to reproduce with, though some species can “self”, combining their own products of meiosis with each other. This process still results in an increase in diversity, as the offspring can still differ from the parent due to the novel recombinations that occur during meiosis. Finding a partner might be a passive process, such as release into the ocean, or a more active one, such as courtship rituals performed by birds of paradise.

    Organisms that undergo sexual reproduction have a defined life cycle that describes the events from fertilization to meiosis and back again. The type of life cycle an organism has can offer insight into its evolutionary history, as well as its ecology. In this lab, you will learn the process of meiosis and the three generalized life cycles of multicellular eukaryotes.

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