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MEIOSIS NOTES
1. WHY MEIOSIS? Why don’t we look exactly like our siblings or parents? One main
reason is because of how sperm and egg are made. Sperm and egg are created through the
process of cell division called meiosis. In meiosis, DNA from mom and dad are reshuffled
and new combinations of chromosomes end in our sperm and egg. If you could create 1
trillion sperm or eggs, every sperm and egg will always be different! Differences, aka
variations, are what help us adapt to our environment.
2. HOW DOES CELL DIVISION (MITOSIS AND MEIOSIS) IMPACT OUR LIFE????
To make a baby, mom and dad go through meiosis to create the sex cells, or gametes. Meiosis
occurs in special diploid cells in males and females which contain 46 chromosomes. Meiosis
in male testicles, aka testes, creates sperm. Meiosis in female ovaries creates egg cells. The
gametes are now haploid and contain 23 chromosomes each. Males make 125 million sperm
per day and females are born with 2 million follicles, of which only about 400 will become
eggs! Only 1 egg is released each month for possible fertilization. If the egg is not fertilized, it
is released from the body through menstruation. Meiosis usually begins at age 12 (puberty); it
continues in males until death and stops in women during menopause at age 50.
When a sperm fertilizes an egg, a zygote is created which becomes diploid again with 46
chromosomes again. The zygote uses mitosis to grow into an adult and to replace old, dead
or damaged cells.
(process of cell division)
Meiosis
(process of cell division)
(process of cell division)
(process of cell division)
process where sperm meets egg
In males, meiosis is called spermatogenesis
and results in 4 sperm, and in females, it is
called oogenesis and it results in only 1 egg
because the other 3 die because one egg must
get all the cytoplasm and machinery to support
a developing zygote if fertilized!
Use the following words
to label the picture:
 Meiosis
 Ovaries
 Zygote
 Testes
 Adult
 Sperm
 Egg
 Fertilization
 Child
 Mitosis
 Mitosis
THE PURPOSE OF MITOSIS and MEIOSIS
Summary: Mitosis v. Meiosis
1. Mitosis results in the production of two genetically identical diploid somatic (body) cells
a. One diploid cell results in two diploid daughter cells
b. The two daughter cells have sets of chromosomes identical to each other and the
original cell.
c. Allows an organism to grow and replace cells
d. Mitosis occurs in somatic cells: any cell in the body that’s not a reproductive cell
*Remember: MITOsis is the division of body cells. My TOE is part of my body.
2. Meiosis results in the production of four genetically different haploid gametes (sex cells)
a. Begins with a diploid cell but produces four haploid daughter cells
b. These daughter cells are genetically different from each other and from the original
diploid parent cell.
c. This is how sexually reproducing organism produces gametes (sex cells)
d. Meiosis occurs in reproductive cells like the ovaries and testes
*Remember: MEiosis forms sex cells. Sperm and egg make ME.
Compare and Contrast: In the space below, write at least 3 differences between mitosis and
meiosis