1. Meiosis Chapter 10.2-3
Produces
* FOUR sex cells
* each has
HALF the number of
chromosomes
of the parent’s cell
(2 mitosis cycles in a row)

2. Why must
 sex cells
(gametes)
have HALF
the number
of Normal cells have
chromosomes two sets of chromosomes,
one from each parent
of a normal So each sex cell can have only one set,
cell? which is half the number of a normal cell.

3. Meiosis
 process which produces gametes which contain
gametes
half the number of chromosomes
as the parent’s body cells
How many male gametes are
produced?
4 sperm
How many female gametes are
produced?
1 egg and
3 polar bodies
Egg

4. Body somatic
Diploid 2n
cell cell
 A normal cell with
two sets of chromosomes
– one from each parent
An illustration of an organisms
chromosomes is called a karyotype.

5. How similar are human and
chimpanzee chromosomes?
Very
similar!
This illustration shows human
chromosomes next to chimpanzee
chromosomes. We have 46, they
have 48. Look at chromosome 2.

6. sex
Haploid n gamete
cell
 A cell with one set of chromosomes,
half of the normal amount

7. Homologous chromosomes
 A matching pair of same chromosome, one
from each parent
– each chromosome has genes for the same
traits

8. sperm
 Male gamete, a haploid sex cell (n)

9. Egg
 Female gamete, a haploid sex cell (n)

10. Sexual reproduction
Involves the production (meiosis)
and fusion (fertilization)
of haploid gametes (sperm and egg)

11. Meiosis phase 1(pg 268)
Process that produces 2 haploid cells
which are NOT identical
– both cells have only
one of each of a cell’s homologous pairs
(already DOUBLED and has cross-overs)

12. Crossing over
When sections of
homologous
chromosomes
cross over each
other and genes
are traded or
switched

13. Meiosis phase 2
Process that produces 4 haploid cells
– none of which are identical
– each has one of each original homologous pair (with
cross overs)

14. Meiosis phase 1 and 2
Process that produces 4 haploid cells
– none of which are identical
– each has one of each original homologous pair (with
cross overs)

15. Genetic recombination
 Increases differences among offspring
– caused by meiosis and
 - increased by the crossing over of
chromosomes

16. Sister chromatids
 identical copies of a chromosome
connected by a centromere

17. Nondisjunction
 The failure of
homologous
chromosomes to
separate and go
to different cells
during meiosis,
resulting in
gametes that
have an abnormal
number of
chromosomes

18. Polyploidy
many normal number of
chromosomes
 the condition of
having three, four,
or more sets of
chromosomes
instead of the two
normally present in
diploids

19. spermatogenesis
creation
 Process in which 4 haploid sperm are
produced

20. oogenesis
 Process in which 1 haploid egg and 3
polar bodies are produced

21. polar bodies
 Three of the haploid cells produced in
oogenesis,
 they cannot be fertilized by sperm

22. And now a quiz…
 What’s the difference between mitosis and meiosis?
 Mitosis produces Meiosis produces
two
identical four
diploid different
nuclei haploid
in body gametes
cells in two phases
This illustration does not show that
chromosomes cross over, which would make each gamete
unique.

23. Mahalo!