MEIOSIS 2

Meiosis

CELL DIVISION/MEIOSIS

What is meiosis? 

  1. Meiosis is a cell division that produces the sex cells or the gametes. (for example: the sperms and the eggs)
  2. Meiosis produces four daughter cells that are NOT IDENTICAL (not the same).
  3. Sometimes meiosis is referred to as thereduction of the chromosomes because cells that are produced by meiosis have half the number of chromosomes as the parent cells.

        Meiosis

        Parent cell

         Four daughter cells

        1. How are these daughter cells similar to each other? 
        2. How are they different from each other?
        3. How do they compare to the parent cell?

        Note: 
        • Only  sex cells are produced by meiosis
        • Meiosis only takes place in the testis of males and ovaries of females

        For more information, click on this:

        List three events that occur in meiosis that are responsible for diversity in sexually reproducing organisms.
        1. Crossing-over
        2. Independent assortment
        3. Two consecutive cell divisions
        What are sex cells?
        1. Sex cells or gametes are the sperms and the eggs.
        2. These cells have half the number of chromosomes as the body cells.
        3. Additionally, each of the sperm cells or the eggs has adifferent combination of chromosomes to each other.
        4. The male sex cells or sperms are produced in the male testis, and the female sex cells or eggs are produced in the ovaries

        -How are sperm cells different from egg cells?
        -How are they similar? 


        LOOK AT THESE SPERM CELLS!


        CHECK OUT THIS EGG CELL!


        Where do you get your genes from? 
        1. You inherit (get) your genes from your parents.
        2. You receive half of your genes from your mom and the other half from your dad.
        3. The sperm brings the half from your dad and the egg brings the half from you mom.

        If you and your siblings are receiving genes from the same parents, how come you are not identical?

        HEREDITY: 
        IS THE PASSING OF TRAITS FROM PARENTS TO OFFSPRING

        NOTE:  CELLS PRODUCED BY MEIOSIS EACH HAS A UNIQUE COMBINATION
        • For example, each time a man ejaculates, he releases 3 million to 5 million sperms and each sperm has a slightly different combination.

        Why do you think it is necessary for a man to release so many sperms?

        How are cells produced by mitosis different from cells produced by meiosis?
        • In cells produced by mitosis the chromosomes are in pairs.
        • In cells produced by meiosis the chromosomes are not in pairs.
        Learn more here:


        What are three types of reproduction?
        1. Asexual reproduction
        2. Sexual reproduction
        3. Cloning.

        How is a asexual reproduction different from sexual reproduction?
        • Asexual reproduction involves just one parent and theoffspring are identical to the parent.
        • Sexual reproduction involves two parents and theoffspring are similar, but not identical either parent.

        Additional questions
        • What are some advantages of sexual reproduction?
        • What are some disadvantages of sexual reproduction?
        • What are some advantages of asexual reproduction?
        • What are some disadvantages of asexual reproduction?

        What are 3 types of asexual reproduction?
        1. fragmentation
        2. binary fission
        3. budding.

        Fragmentation
        Occurs in star fish. For instance, if you step on a star fish and break in four pieces, as long as each part contains portion of the nucleus, each part of the star fish will become a new organism.

        Budding
        Some organisms like certain plants are able to form a bud. This bud can fall to the ground and grow to become a new plant.

        Binary fission
        A process similar to mitosis that bacteria use to reproduce

        What is FERTILIZATION?
        • Fertilization is the union of the sperm and the egg. Zygote is the new cell that is formed by the egg and the sperm.

        What is cloning?
        Cloning is a technique that produces the same end result as asexual reproduction.Cloning produces organisms that are identical. This procedure involves the removal of nucleus from one cell and placing it into another cell.

        Is there an advantage to sexual reproduction?
        Yes, Sexual reproduction creates differences or diversity. Because sexual reproduction creates so many different combination, when the environment changes, there is a better chance that some organisms will survive.

        FOR INSTANCE, if two members of the same family are exposed to H1N1, however, it is possible that only one of them dies from the disease and the other member is not affected. If they were identical, if one dies, the other would also die. Sexual reproduction increases the chances for survival when there is change in the environment.

        Is there a disadvantage to sexual reproduction? 
        • You cannot guaranty the expression of the desirable trait.
        • Undesirable recessive traits may be expressed.
        • Produces less offspring
        • Reproduces slower
        • Requires two parents

        Is there an advantage to asexual reproduction?
        • Offspring are identical
        • Requires only one parent
        • Produces more offspring
        • Reproduces much faster

        Is there a disadvantage to asexual reproduction?
        • Lack of diversity

        REVIEW QUESTIONS
        What is mitosis?
        • Mitosis is a cell division that produces two daughter cells that are identical.
        What is meiosis?
        • Meiosis is a cell division that produces the sex cells or the gametes.
        Where does meiosis occur? 
        • Meiosis only occurs in the male testis and the female ovaries.
        How are cells produced by mitosis different from cells produced by meiosis?
        • Cells produced by mitosis have a full set of chromosomes and cells produced by meiosis have half the number of chromosomes as the organism
        In reference to evolution, what type of cell division came first, mitosis or meiosis?
        • First, we must acknowledge that meiosis only occurs in sexually reproducing organisms. Since the first life forms were asexually reproducing organisms, meiosis is an evolutionary trait. Therefore, it is logical to conclude that mitosis came first.
        Where does fertilization occur?
        • Fertilization occurs in the Fallopian tube or oviduct.
        What happens after the egg is fertilized?
        • The new cell, the zygote moves to the uterus where the baby will grow and develop through mitotic cell division.
        The most important thing to remember about meiosis is:
        • It reduces the chromosome number in half.
        • It is one of the mechanisms responsible for the diversity or differences in organisms and that is because each sperm or egg created by meiosis is different.

        THINK!
        How would the world be different, if humans could only reproduce asexually?

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