The document discusses meiosis and how it differs from mitosis. Meiosis produces gametes with half the number of chromosomes as body cells through two cell divisions. In the first division, homologous chromosomes pair up and may exchange DNA through crossing over, then separate. This leads to independent assortment of chromosomes. The second division separates sister chromatids, resulting in four haploid cells. Meiosis ensures fertilization restores the diploid number through halving the number of chromosomes in gametes.

1. Interest Grabber
1. How many chromosomes would a sperm or an egg contain if
either one resulted from the process of mitosis?

2. Interest Grabber
1. How many chromosomes would a sperm or an egg contain if
either one resulted from the process of mitosis?
46 chromosomes

3. Interest Grabber
2. If a sperm containing 46 chromosomes fused with an egg
containing 46 chromosomes, how many chromosomes would the
resulting fertilized egg contain? Do you think this would create
any problems in the developing embryo?

4. Interest Grabber
2. If a sperm containing 46 chromosomes fused with an egg
containing 46 chromosomes, how many chromosomes would the
resulting fertilized egg contain? Do you think this would create
any problems in the developing embryo?
46 + 46 = 92; a developing embryo would not survive if it
contained 92 chromosomes.

5. Interest Grabber
3. In order to produce a fertilized egg with the appropriate
number of chromosomes (46), how many chromosomes should
each sperm and egg have?

6. Interest Grabber
3. In order to produce a fertilized egg with the appropriate
number of chromosomes (46), how many chromosomes should
each sperm and egg have?
Sperm and egg should each have 23 chromosomes.

7. MEIOSIS
10.1
Making gametes…
All living things…
reproduce.

8. ASEXUAL REPRODUCTION
Bacteria reproduce
using binary fission
Budding and
regeneration are
used by plants and
animals to reproduce
asexually (mitosis)

9. BINARY FISSION & MITOSIS
Produces cells that are identical copies
of parent cells.

10. ADVANTAGES OF
ASEXUAL REPRODUCTION
• Can make offspring
faster
• Don’t need a partner

11. DISVANTAGES OF
ASEXUAL REPRODUCTION
• All offspring are
alike
• Species cannot
adapt and change
• One disease can
wipe out whole
population

12. SEXUAL REPRODUCTION
Combines the genetic
material from two parents
(sperm and egg) so
offspring are genetically
different.

13. ADVANTAGES OF
SEXUAL REPRODUCTION
• Allows for variation in population
• Individuals can be different
• Provides foundation for EVOLUTION
• Allow species to adapt to changes in their
environment

14. EGG + SPERM 
If egg and sperm had same number
of chromosomes as other body cells .
. .
…baby would have too many
chromosomes!

15. MEIOSIS is the way…
to make cells
with half the
number of
chromosomes
for sexual
reproduction

16. DIPLOID & HAPLOID
Most cells have 2 copies of each chromosome
(one from mom; one from dad)
These cells are diploid (2n) and are called:
HOMOLOGOUS
CHROMOSOMES
Body cells (aka somatic cells) are diploid (2n)

17. HOMOLOGOUS CHROMOSOMES
• Same size
• Same shape
• Carry genes for the same
trait
• But are NOT identical!
(Don’t have to have the
SAME CHOICES)

18. DIPLOID & HAPLOID
• Some cells have only one copy of
each chromosome.
• These cells are haploid (1n)
• All sperm and egg cells are haploid

19. MITOSIS
• Makes 2 cells genetically identical
to parent cell and to each other
• Makes 2n cells
• Makes somatic (body) cells
• Used by organisms to:
– increase size of organism,
– repair injuries,
– replace worn out cells

20. MEIOSIS
• Makes 4 cells genetically
different from parent cell
& from each other
• Makes 1n cells
• Makes germ cells or
gametes (sperm & egg)
• Used for sexual
reproduction

21. WHAT MAKES MEIOSIS DIFFERENT ?
1. Synapsis and Crossing over during
(PROPHASE I)
1. Segregation and Independent
Assortment during (ANAPHASE I)
3. Skip Interphase II (NO Synthesis)
CELL DIVIDES TWICE, BUT…
ONLY COPIES DNA ONCE

22. WHAT MAKES MEIOSIS DIFFERENT? #1
Homologous chromosomes pair up
during Prophase I = Synapsis
This group of FOUR (4)
chromatids is called a
Tetrad.

23. WHAT MAKES MEIOSIS DIFFERENT? #1
Exchange of DNA between
homologous pairs = crossing over
during Prophase I
Allows for shuffling
of genetic material

24. WHAT MAKES MEIOSIS DIFFERENT? #1
CROSSING
OVER
• Allows for rearranging of DNA in different
combinations
• After crossing over, chromatid arms are
not identical anymore

25. WHAT MAKES MEIOSIS DIFFERENT? #2
Separation of homologous
chromosomes during ANAPHASE I
• Segregation
• Independent Assortment
Separates gene choices and allows
shuffling of genetic material

26. WHAT MAKES MEIOSIS DIFFERENT? #2
SEGREGATION
(Anaphase I)

27. WHAT MAKES MEIOSIS DIFFERENT? #2
SEGREGATION & CROSSING OVER
together make even more combinations

28. WHAT MAKES MEIOSIS DIFFERENT? #2
INDEPENDENT ASSORTMENT

29. WHAT MAKES MEIOSIS DIFFERENT? #2
INDEPENDENT ASSORTMENT at ANAPHASE I
Lots of different
combinations are
possible!
This is why you don’t
look exactly like
your brothers and
sisters even
though you share
the same parents!

30. WHAT MAKES MEIOSIS DIFFERENT
recap so far:
• Crossing over, independent assortment
and segregation are all ways MEIOSIS
results in genetic recombination
• So daughter cells are different from
parents and from each other

31. WHAT MAKES MEIOSIS DIFFERENT? #3
Skip INTERPHASE II (No Synthesis)
CELL DIVIDES TWICE, BUT …
…ONLY COPIES ITS DNA ONCE
MITOSIS:
G1  S  G2  P  M  A  T  C
MEIOSIS:
S G2 P M A T C
G1       
P  M  A  T 
C
( I )
( II )

32. Go to
Section:
Meiosis I
Section 11-4
Figure 11-15 Meiosis

33. Go to
Section:
Meiosis I
Section 11-4
Figure 11-15 Meiosis

34. Go to
Section:
Meiosis I
Section 11-4
Figure 11-15 Meiosis

35. Section 11-4
Go to
Section:
Figure 11-15 Meiosis
Meiosis I

36. Section 11-4
Go to
Section:
Figure 11-15 Meiosis
Meiosis I

37. Prophase II Metaphase II Anaphase II Telophase II
Go to
Section:
Meiosis II
Meiosis I results in two
haploid (N) daughter cells,
each with half the number of
chromosomes as the original.
The chromosomes line up in
a similar way to the
metaphase stage of mitosis.
The sister chromatids
separate and move toward
opposite ends of the cell.
Meiosis II results in four
haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II

38. Prophase II Metaphase II Anaphase II Telophase II
Go to
Section:
Meiosis II
Meiosis I results in two
haploid (N) daughter cells,
each with half the number of
chromosomes as the original.
The chromosomes line up in
a similar way to the
metaphase stage of mitosis.
The sister chromatids
separate and move toward
opposite ends of the cell.
Meiosis II results in four
haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II

39. Prophase II Metaphase II Anaphase II Telophase II
Go to
Section:
Meiosis II
Meiosis I results in two
haploid (N) daughter cells,
each with half the number of
chromosomes as the original.
The chromosomes line up in
a similar way to the
metaphase stage of mitosis.
The sister chromatids
separate and move toward
opposite ends of the cell.
Meiosis II results in four
haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II

40. Prophase II Metaphase II Anaphase II Telophase II
Go to
Section:
Meiosis II
Meiosis I results in two
haploid (N) daughter cells,
each with half the number of
chromosomes as the original.
The chromosomes line up in
a similar way to the
metaphase stage of mitosis.
The sister chromatids
separate and move toward
opposite ends of the cell.
Meiosis II results in four
haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II

41. Prophase II Metaphase II Anaphase II Telophase II
Go to
Section:
Meiosis II
Meiosis I results in two
haploid (N) daughter cells,
each with half the number of
chromosomes as the original.
The chromosomes line up in
a similar way to the
metaphase stage of mitosis.
The sister chromatids
separate and move toward
opposite ends of the cell.
Meiosis II results in four
haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II

42. Ways Meiosis is different:
• Homologous pairs match up & trade DNA
(SYNAPSIS & CROSSING OVER) in
PROPHASE I
• SEGREGATION
& INDEPENDENT ASSORTMENT
in Anaphase I
create genetic recombination
• Skipping INTERPHASE II-
• (Dividing TWICE but copying DNA once)
produces 1n cells