GN 301 Module 2: Mitosis and Meiosis

Mitosis

Purpose of mitosis:

  • to replicate identical cells for different functions in the body

Define ==somatic cell==:

  • a cell that does not produce gametes

List stages and what happens in each stage

  1. ==Prophase:== The chromosomes shorten and thicken. (60% of time)
  2. ==Metaphase:== Chromosomes line up in the middle of the cell. (5% of time)
  3. ==Anaphase:==  Chromatids break apart at the centromere and move to opposite poles. (5% of time)
  4. ==Telophase:== Two nuclei formed after nuclear envelopes reform around each group of chromosomes. (30% of time)

Define ==Cytokinesis==

  • the cytoplasmic division of a cell at the end of mitosis, bringing about the separation into two daughter cells. \n
Synchronized Swimming Mitosis Video

  • What do the green noodles represent?

    • Spindle fibers.

  • What do the people holding the green noodles represent?

    • centrioles

  • What do the swimmers with the swim caps represent?

    • cell membrane

Meiosis

  • Define ==meiosis==:
    • Cell division in a diploid cell that leads to gamete formation.
  • Two division – what happens in each?
    • Reductional division: The number of chromosomes in daughter cells gets cut in half from the original number.
    • Equational division: The chromosome number is the same at the end as it was at the beginning.
  • Define ==crossing over== and describe its importance:
    • Crossing over is recombination in Prophase I. 2 chromosomes come together and break apart when they overlap and switch some of their alleles. This allows variation from generation to generation as alleles switch around.

List the stages of meiosis and what happens in each

==MEIOSIS I==

  1. Prophase I:
  • The chromosomes begin to condense and pair up, aligning with their partner so they can match up at corresponding positions along full length.
  1. Crossing over:
  • chromosomes shuffle their alleles between each other
  1. Metaphase I:
  • homologue pairs line up at the metaphase plate for separation
  1. Anaphase I:
  • Homologues break apart and move to opposite ends of the cell, while the sister chromatids remain attached
  1. Telophase I:
  • The chromosomes end up on opposite poles of the cell, starting cytokinesis and producing 2 haploid daughter cells

==MEIOSIS II==

  1. Prophase II:
  • chromosomes condense and, if needed, the nuclear envelope breaks down. The centrosomes move apart, forming the spindle, which begins to capture chromosomes
  1. Metaphase II:
  • The chromosomes line up individually on the metaphase plate
  1. Anaphase II:
  • the sister chromatids separate and move to opposite ends of the cell
  1. Telophase II:
  • Nuclear membranes form along the chromosomes, allowing them to decondense and start cytokinesis, which produces 4 haploid cells (which are sperm or egg cells) \n
Biological Significance of meiosis

  • ==Constant Number of chromosomes== (along with fertilization)

    • Since meiosis creates cells that become gametes, it’s important that the chromosome number is reduced to the original size because it would not be good if there were twice the number of original chromosomes.

  • ==Provides variation from generation to generation== (2 ways)

    • 1. crossing over: shuffling chromosomes between parents
    • 2.  independent assortment: genes independently separate themselves from one another when reproductive cells develop

Compare Mitosis and Meiosis

  • Meiosis is vital for fertilization.
    • Mitosis is vital for cell replication for different tasks in the body.
  • Meiosis maintains a constant number of chromosomes.
    • Mitosis does not pair chromosomes and so it ends up producing twice the original amount of cells.
  • Meiosis provides variation from generation to generation.
    • Mitosis replicates the exact same cell without any variation.
  • Meiosis shuffles chromosomes between parents (there are 2^23 possible combinations of chromosomes).
    • Mitosis creates the same mitotic problems each time.