HOW CELLS DIVIDE
BACKGROUND ON MEIOSIS AND MITOSIS
As viewed from a human perspective, nature seems to have done ingenious engineering to overcome
obstacles. Take the evolution of sex, for instance. To make the move from asexual to sexual reproduction,
nature took a system by which parent cells reproduced simply by dividing (asexual reproduction) and altered
it to allow two parent cells to combine to create offspring (sexual reproduction).
Asexual reproduction relies on a process called mitosis, in which the nucleus of a cell divides to create two
new nuclei, each containing an identical copy of DNA. Mitosis allows the cells in your body to divide and
regenerate—your hair to grow, your skin to heal after being wounded. Almost all of the DNA duplication in
your body is carried out through mitosis.
Meiosis, on the other hand, is the process by which certain sex cells, or gametes, are created. If you're
male, your body uses meiosis to create sperm cells; if you're female, it uses meiosis to create egg cells.
While all other cells in your body contain 46 chromosomes (23 from your father and 23 from your mother),
your egg (or sperm) cells contain only half that number—a total of 23 chromosomes. When an egg and sperm
unite to make a fertilized egg, the chromosomes add up to equal 46.
How exactly does meiosis halve and mix chromosomes? Find out through this feature, which provides a
step-by-step, side-by-side comparison of meiosis and mitosis. Go to the following website and click on the
link “Launch Interactive”.
http://www.pbs.org/wgbh/nova/body/how-cells-divide.html
Complete the following as you work through the interactive website.
Slide 1:
Mitosis produces ______ cells that are ______________________, each containing ______
chromosomes for humans. Meiosis produces ______ cells that are all genetically different, each containing
_______ chromosomes.
Slide 2: Interphase
Is interphase the same for mitosis and meiosis? Circle one
What occurs during interphase?
YES or NO
For Slides 3-18 you are going to compare what you see happening in mitosis and meiosis on the chart below.
Use drawings to help you. Make sure to watch the video with each slide to see the animations as they occur.
Mitosis
Meiosis
Prophase
Prophase I
Prometaphase
Prometaphase I
Metaphase
Metaphase I
Anaphase
Anaphase I
Telophase
Telophase I
Cytokinesis
Cytokinesis I
The end result is 2 cells, each identical to each
Interphase II (not all organisms do this)
other and the original. They will contain 46
chromosomes and will immediately be in Interphase
again.
Prophase II
Prometaphase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis (II)
The end result is four cells, all that are genetically
different. They each contain 23 chromosomes for
humans, and are used for reproduction.