1. Sexual Reproduction
and Meiosis
Chapter 4 Lesson 1
p.116-126

2. Cell Division
Mitosis
• Body cells
Meiosis
• Sex cells
– Sperm and Egg
Cells

3. Meiosis
• A special kind of cell division that end in four
cells with half the number of chromosomes.
• Creates sex cells (egg cells and sperm cells)
• The original cell has 46 chromosomes.
• The final four cells has 23 chromosomes each.

5. Sexual Reproduction
• When two parents make one offspring.
• Two different sex cells combine to form an
offspring.
• An egg is a female sex cell.
• A sperm is a male sex cell.
• Fertilization is the joining of an egg and a sperm.
• A fertilized egg cell is called a zygote.

6. Chromosomes
• Human cells have 46 chromosomes, or
23 pairs of chromosomes.
• 23 of our chromosomes come from our
mom.
• 23 of our chromosomes come from our
dad.

9. Chromosomes
• Each pair of chromosomes have the
same type of information.
• One set from mom
• One set from dad

10. Mom Dad
Gene for
Eye Color

11. Mom Dad
Gene for
Eye Color
Mom Dad
Before DNA is replicated,
copied during interphase.
Duplicated Chromosomes
after interphase.

12. Dad
Gene for
Eye Color
Homologous Pairs of chromosomes have
genes for the same traits.
Mom

13. Mom Dad
These are still homologous pairs. Now they are
just duplicated.

14. We have 23 homologous pairs.

15. Sexual Reproduction
• Body cells have a full set of
chromosomes in homologous pairs.
• We call these cells diploid.
• Sex cells have half the number of
chromosomes.
• They do not have homologous pairs.
• We call them haploid. (half)

16. • In meiosis, one
diploid cell
divides and
makes four
haploid cells.

17. • When
fertilization
occurs, the new
cell, called a
zygote, will
have the
normal number
of cells.
Diploid
(2N)
Haploid
(N)
Haploid
(N)

19. Different organisms have different
numbers of chromosomes.
– How many homologous pairs does each species
have?

20. Stages of Meiosis

22. Fig. 2.7 ©Scion Publishing Ltd
The stages of meiosis.
Meiosis is used only for the
production of sperm and eggs.
It consists of two successive cell
divisions, producing four
daughter cells (although in
oogenesis only one of these
develops into a mature oocyte;
the others form the polar
bodies).
Meiosis has two main functions:
to reduce the chromosome
number in the gamete to 23, and
to ensure that every gamete is
genetically unique.

25. Growth and Development
• After fertilization a single celled zygote is
formed.
• The zygote will go through mitosis and cell
division to become an organism.
MITOSIS MEIOSIS
MEIOSIS I
Prophase I
Chromosome
replication
Homologous
chromosome
pair
Chromosome
replication
2n = 6
Parent cell
Prophase
Replicated chromosome
Metaphase Metaphase I
Anaphase I
Telophase I
Haploid
n = 3
Daughter
cells of
meiosis I
MEIOSIS II
Daughter cells of meiosis II
nnnn
2n2n
Daughter cells
of mitosis
Anaphase
Telophase

26. • Choose one color to be the maternal
chromosome.
• Choose one color to be the paternal
chromosome.

27. • Cut a maternal and paternal chromosome
to both be 5cm long.
• Then, cut a maternal and paternal
chromosome to be both 8cm long.

28. • Chromosome 1
• Chromosome 2

29. How many chromosomes does the cell have
total?
• Chromosome 1
• Chromosome 2

43. Cell Division
Mitosis Meiosis