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    Meiosis, independent assortment

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    Eukaryotic cells can divide by mitosis or meiosis. In humans, mitosis produces new cells for growth and repair; meiosis produces sex cells (gametes) called sperm and eggs.
    Although mutations are the ultimate source of genetic variability, both meiosis and sexual reproduction also can contribute to new genetic combinations in offspring.

    How do both meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents? Be sure to talk about the two specific steps in meiosis that increase variability as well as the process of fertilization.

    © BrainMass Inc. brainmass.com December 24, 2021, 11:24 pm ad1c9bdddf
    https://brainmass.com/biology/mutation/meiosis-independent-assortment-565584

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    Eukaryotic cells can divide by mitosis or meiosis. In humans, mitosis produces new cells for growth and repair; meiosis produces sex cells (gametes) called sperm and eggs.
    Although mutations are the ultimate source of genetic variability, both meiosis and sexual reproduction also can contribute to new genetic combinations in offspring.
    How do both meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents? Be sure to talk about the two specific steps in meiosis that increase variability as well as the process of fertilization.

    Meiosis produce offspring that differ genetically from the parents by several steps:
    Let look at the stage of meiosis first

    Interphase- is the step where chromosomes duplicate. This stage is where each chromosome consists of two genetically identical sister chromatids attached together.

    Prophase I is the most complex phase of meiosis and take the longest. In this stage, the chromatin coils up and chromosome becomes visible with microscope. In this stage, homologous chromosome composed of two sister chromatids come together as pairs called synapsis The structure consists of four chromatids called a tetrad. During this process of synapsis, chromatids of homologous chromosomes exchange segments in a process called crossing over. Crossing over is the step in which it contributes to the genetic variability. Because the genes on a chromosome or one of its chromatids may be different from those on its homologue, it is thought that crossing over rearranges genetic information. As a result, the genetic shuffling produced by crossing over can produce offspring that differ genetically from the parents.

    Metaphase I
    The stage where chromosome tetrads are aligned on the metaphase plate. Each chromosome is condensed and the sister chromatid attached at their centromere. In each tetrad, the homologous chromosomes are held together at sites of crossing over.

    Anaphase I - where chromosomes migrate toward the two poles of the cell. In contrast to mitosis, the sister chromatid making up each doubled chromosomes remain attached at their centromeres. Homologous chromosomes separate while sister chromatids remain attached.

    Telophase I- cytokinesis occur and you have two haploid daughter cells

    Meiosis II- No further chromosome duplication. sister chromatids separate during anaphase II

    The stages where there offsprings are produced that are genetically different from the parents happen during the crossing over occur in prophase I of meiosis when homologous chromosomes are paired along their length. Crossing over is an exchange of genes between two homologous chromosomes that contribute to the genetic variability.
    The other stages that can contribute to genetic variability in the offspring is the independent arrangement of homologous chromosome pairs at metaphase of meiosis I that affects the resulting gametes. The orientation of the homologous pairs of chromosomes tetrads at metaphase I from the maternal or paternal chromosome is random just like the flip of a coin. There is a 50% chance that a particular daughter cell will get the maternal chromosome of a certain homologous pair and a 50% chance that it will receive the paternal chromosome. So there are two possible ways that the two tetrads can align during metaphase I.

    Another possibility of genetic variation in the offsprings is when meiosis fail to occur normally. The meiotic spindle distributes chromosomes to daughter cells without error most of the time. Sometime, there can be errors that lead to nondisjunction in which members of chromosome pair fail to separate. When a homologous pair of chromosomes does not separate during meiosis I, this lead to gametes with abnormal numbers of chromosomes. For example, one gametes can have three chromosomes and the others can have two or one chromosomes. This also lead to genetic variability of the offsprings.

    Sexual reproduction happen in meiosis so the steps are the same and it contributes to genetic variation just like meiosis.

    This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!

    © BrainMass Inc. brainmass.com December 24, 2021, 11:24 pm ad1c9bdddf>
    https://brainmass.com/biology/mutation/meiosis-independent-assortment-565584

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