meiosis(bio) - Meiosis and Sexual Life Cycles - 1 We have...

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Meiosis and Sexual Life Cycles - 1 We have just finished looking at the process of mitosis, which ensures that each cell of an organism has the same DNA as the original fertilized egg or zygote (absent mutations). Transmitting chromosomes and genetic information from generation to generation is equally important. A critical role of heredity is to maintain and obtain variation among members of a species. These variations are the result of the specific genes we inherit from our parents. We did not always know that genes were located on chromosomes. We didn't even know how genetic information was transmitted from parent to offspring. The mechanism for transmitting genetic information was first proposed by Gregor Mendel in the mid-1800's. It was pretty much forgotten until the early 1900's when Mendel's papers were "discovered" about the time other researchers were drawing the same conclusions based on similar research. Soon after, Walter Sutton showed that Mendel's principles of inheritance applied to chromosomes and that chromosomes are the units of heredity. We shall discuss Mendel's principles and inheritance patterns soon, but first we'll look at how chromosomes are transmitted from generation to generation by the process of meiosis and sexual reproduction . Although asexual reproduction, which uses mitosis to make new individuals (genetically the same as the parent) is common in protists, plants, fungi and some animals, most organisms produce offspring by a process of sexual reproduction, in which a gamete from one parent joins a gamete from the other parent to form a zygote (or fertilized egg). This process results in offspring that have a combination of parental chromosomes. However, each generation of a species retains the same chromosome number as the preceding generations. Meiosis is the process that ensures that each new generation has the same chromosome number as the preceding generation. Meiosis is a process that reduces chromosome number by half and occurs at just one stage in an organism's life cycle (to form gametes in animals, or to start the gamete producing stage in plants, or for some organisms to restore the appropriate chromosome number for the assimilative stage of its life history). Sexual reproduction then restores the "typical" number of chromosomes for the next generation. In this context, we need to look not just at the process of meiosis, but also take a look at the sexual life cycles of organisms. In addition to providing a mechanism to reduce chromosome number for sexual reproduction, meiosis has a second, most important function for living organisms: maintaining genetic variation . Each time meiosis occurs, followed by, at some point, sexual reproduction, the new individual is genetically different from either parent. Because meiosis is involved with genetic variation and is needed for sexual reproduction, we will discuss this important genetic function of meiosis as well as its chromosome reduction function in this section.
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meiosis(bio) - Meiosis and Sexual Life Cycles - 1 We have...

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