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Meiosis

Meiosis

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This lesson will explore the process of meiosis in developing sperm and egg cells.

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Tutorial

What's Covered

This lesson is going to cover the process of Meiosis by looking at

  1. Meiosis
  2. Meiosis I
  3. Meiosis II

1.Meiosis

Meiosis is a type of cell division that is specific to sex cells. In this type of cell division, germ cells are going through a division in order to form gametes, which are sperm cells or egg cells. The result of meiosis is haploid daughter cells, and haploid cells contain half as many chromosomes as the original parent cell.

ExampleIn humans, meiosis starts out with a germ cell of 46 chromosomes and ends up with haploid daughter cells that each have 23 chromosomes.

Terms to Know

    • Meiosis
    • A type of cell division that occurs in sex cells to produce haploid gametes.
    • Haploid
    • The number of chromosomes in the gametes of an organism which is equal to half of the number of chromosomes of somatic cells.
    • Gamete
    • A sex cell such as sperm or egg which contains a haploid number of chromosomes.

There are two rounds of cell division to form gametes, called meiosis I and meiosis II. Each round of meiosis is similar to mitosis. There are two types of meiosis depending on if it is creating a sperm or an egg gamete:

  • Spermatogenesis is meiosis in sperm cells and leads to four sperm cells.
  • Oogenesis is the formation of egg cells and leads to one egg cell and a polar body.

Terms to Know

    • Meiosis I
    • The first round of cell division in meiosis.
    • Meiosis II
    • The second round of cell division in meiosis.
    • Spermatogenesis
    • The process that forms 4 haploid sperm cells.
    • Oogenesis
    • The process that forms a haploid egg cell and a polar body.

2. Meiosis I

The process of meiosis is similar to mitosis.

  • The germ cell begins in prophase I. In this phase, similar to prophase of mitosis, homologous chromosomes will condense and pair and also swap segments.The swapping of segments between these chromosomes creates genetic variability. Also during this stage, the nuclear envelope will break down and spindle microtubules will attach to the sister chromatids.
  • In metaphase I, the homologous chromosome pairs will align at the metaphase plates in the middle of the cells.
  • Anaphase I follow, and homologous chromosomes will then start to separate. They start moving towards the opposite ends of the cell.
  • During telophase I, the nuclear envelope then starts to reform, and we end up with two haploid nuclei.

The cells still need to go through another round of cell division in order to ensure they end up with only 23 chromosomes in each cell.


3. Meiosis II

After telophase I is done, the cells begin meiosis II.

  • During prophase II, similar to prophase I, spindle microtubules will attach to the sister chromatids and the nuclear envelope will start to break down.
  • In metaphase II, the chromosomes well then again line up at the middle of thecell.
  • In anaphase II, sister chromatids separate, and start moving towards opposite poles.
  • Again, in Telophase II the nuclear envelope will reform. This time the end will result in four haploid nuclei, all that have 23 chromosomes.

The reason sex cells are haploid is because when the sperm fertilizes the egg and the nuclei combine with to form a diploid cell.

Example In humans the both the sperm cell and the egg contain 23 chromosomes which combine to give a total of 46. In you, half of these came from your mother and half from your father.

Term to Know

    • Diploid
    • Cells that contains two sets of each chromosome.

Summary

Meiosis.png

Meiosis is the process of cell division that creates gametes. There are two phases of Meiosis. In Meiosis I the cell goes through prophase I, like in mitosis, homologous chromosomes will condense and pair up. Unlike mitosis, they will also swap segments of themselves to create genetic variability. The cell will move through metaphase I and anaphase I, ending in telophase I with two haploid cells. Meiosis II is similar, but result in four haploid cells.

Keep up the learning and have a great day!

Source: SOURCE: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
  • Meiosis

    A type of cell division that occurs in sex cells to produce haploid gametes.

  • Spermatogenesis

    The process that forms 4 haploid sperm cells.

  • Oogenesis

    The process that forms a haploid egg cell and a polar body.

  • Diploid

    Cells that contains two sets of each chromosome.

  • Haploid

    The number of chromosomes in the gametes of an organism which is equal to half of the number of chromosomes of somatic cells.

  • Meiosis I

    The first round of cell division in meiosis.

  • Meiosis II

    The second round of cell division in meiosis.

  • Gamete

    A sex cell such as sperm or egg which contains a haploid number of chromosomes.