1. Meiosis
Textbook Section 8.3

2. Sexual Reproduction
► Organisms receive half of their
DNA from each parent
► Sperm and eggs cells (haploid)
combine to create a zygote
(diploid)
► Used by most animals, fungi,
plants, and algae

3. Remember…
► Organisms have two
copies of each
chromosome, called
“homologous
chromosomes”
► Can be autosomes or
sex chromosomes

4. Meiosis
► A cell replicates its DNA,
then divides twice, forming
four haploid cells
► Stages are the same, but
they occur TWICE!

5. Meiosis I vs. Meiosis II

6. Steps of Meiosis
► PROPHASE I

7. Steps of Meiosis
► METAPHASE I
 Homologous
chromosomes line up
along center in pairs

8. Steps of Meiosis
► ANAPHASE I
 Sister chromatids DO
NOT separate.
 Homologous
chromosomes DO!
► TELOPHASE I
 Nuclear membrane does
not re-form

9. Steps of Meiosis
► PROPHASE II
 Cell has been split in
two, so all “II” stages
take place in both cells

10. Steps of Meiosis
► METAPHASE II

11. Steps of Meiosis
► ANAPHASE II
 Sister chromatids finally
separate
► TELOPHASE II

12. AN IMPORTANT DIFFERENCE
►In the first cell division, CHROMOSOME
PAIRS (HOMOLOGOUS CHROMOSOMES) are
separated.
►In the second cell division, SISTER
CHROMATIDS are pulled apart.

13. Comparing Mitosis and Meiosis
► Mitosis makes
cells for growth,
development,
repair, and
asexual
reproduction
► Meiosis makes
cells for sexual
reproduction

14. Comparing Mitosis and Meiosis
► Mitosis produces two
cells identical to the
parent cell (diploid -
called daughter cells)
► Meiosis produces four
cells with half the
number of
chromosomes as the
parent (haploid)

15. Comparing Mitosis and Meiosis
► In meiosis, “crossing
over” occurs during
prophase I.
► Chromosomes form tetrads
► Homologous chromosomes
“swap” parts of their DNA
 leads to genetic
variation

16. Sperm vs. Eggs
►Spermatogenesis creates four equally-sized
sperm cells
►Oogenesis creates three tiny cells that will
die (polar bodies) and one large ovum (egg)

17. Spermatogenesis vs. Oogenesis