1. Meiosis in eukaryotic
cells
Stages of meiosis

2. DEFINING MEIOSIS 
Meiosis is a reduction division
Takes place in the Gametes (sperm
and egg) of an organism
Reducing the chromosome number
from 46 in somatic cells to 23 in sex
cells (sperm and egg)

3. Alternating stages
chromosome number
must be reduced
diploid46 
haploid23
2n  n
humans: 46  23
meiosis reduces
chromosome number
makes gametes
fertilization restores
chromosome number
haploid  diploid
n  2n

4. meiosis
 A diploid(2n) cell will contain one set of
chromosomes from the male parent and
one set from the female parent.
 Before cell division there will be two copies
of each chromosome (called homologous
pairs) in the nucleus.
 Two homologous chromosomes will share
the following characteristics:
 Same length
 Centromere in same position
 Same number of genes
 Genes arrange in the same order

5. FIGURE 8.11 A KARYOTYPE SHOWS THAT THE CHROMOSOMES
OCCUR AS PAIRS
8-5

6. THE OVERVIEWOF
MEIOSIS
interphase 1 prophase 1 metaphase 1 anaphase 1
prophase 2 metaphase 2 anaphase 2 telophase 2
telophase 1

7. STAGES OF MEIOSIS
 Requires two divisions
 Meiosis I - the chromosomes of each
homologous pair separate
 Meiosis II - the sister chromatids of each
duplicated chromosome separate

8. MEIOSIS 1:EARLY PROPHASE1
 .
 Chromosomes condense.
 Spindle forms.
 Nuclear envelope fragments.

9. MEIOSIS 1: Late prophase
 Homologs pair.
 Crossing over occurs.

10. PROPHASE 1: CROSSING
OVER
 Homologous chromosomes in a tetrad cross
over each other
 Pieces of chromosomes or genes are
exchanged
 Produces Genetic recombination in the
offspring

11. PROPHASE1: CROSSING
OVER

12. MEIOSIS1: METAPHASE 1
Homologous pairs of chromosomes align
along the equator of the cell

13. MEIOSIS 1:ANAPHASE 1
 Homologs separate and move to opposite
poles.
 Sister chromatids remain
 attached at their centromeres.

14. MEIOSIS 1: TELOPHASE 1
Nuclear envelopes reassemble.
Spindle disappears.
Cytokinesis divides cell into two.

15. MEIOSIS 2:
 Meiosis II produces gametes with
 one copy of each chromosome and thus one
copy of each gene.

16. 16
PROPHASE2
Nuclear envelope
fragments.
Spindle forms.

17. 17
Metaphase 2
Chromosomes align
along equator of cell.

18. 18
Anaphase 2
Sister chromatids
separate and move
to opposite poles.
Equator
Pole

19. 19
TELOPHASE 2
Nuclear envelope
assembles.
Chromosomes
decondense.
Spindle disappears.
Cytokinesis divides cell
into two.

20. 20
Results of Meiosis
Gametes (egg & sperm)
form
Four haploid cells with one
copy of each chromosome
One allele of each gene
Different combinations of
alleles for different genes
along the chromosome

21. Chromosomal Abnormalities
Can Be Inherited
8-21

22. AN ABNORMAL CHROMOSOME NUMBER IS SOMETIMES
TRACEABLE
TO NONDISJUNCTION
 Polyploidy - a eukaryote has three or more complete sets of
chromosomes
 Aneuploidy - an organism has more or less than the normal
number of chromosomes
 Monosomy only one of a type of chromosome
 Trisomy three of a type of chromosome
 Nondisjunction - in meiosis I homologues do not separate
and both go into the same daughter cell, or in meiosis II sister
chromatids fail to separate and both daughter chromosomes go
to the same gamete
8-22

23. FIGURE 8.17B NONDISJUNCTION OF CHROMOSOMES DURING MEIOSIS II OF
OOGENESIS, FOLLOWED BY FERTILIZATION WITH NORMAL SPERM
8-23

24. 8.18 ABNORMAL CHROMOSOME
NUMBERS CAUSE SYNDROMES
 Trisomy 21 (Down Syndrome)
 Over 90% of individuals with Down syndrome have three
copies of chromosome 21
 Abnormal Sex Chromosome Inheritance
 Turner syndrome females are born with only a single X
chromosome
 A male with Klinefelter syndrome has two or more X
chromosomes in addition to a Y chromosome
8-24

25. 8.19 ABNORMAL CHROMOSOME STRUCTURE ALSO
CAUSES SYNDROMES
 Various agents in the environment, such as radiation,
certain organic chemicals, or viruses, can cause
chromosomes to break
 Deletion - an end of a chromosome breaks off or two
simultaneous breaks lead to the loss of an internal segment
 Duplication - the presence of a particular chromosome
segment more than once in the same chromosome
 Inversion - a segment of a chromosome is turned 180
degrees
 Translocation - the movement of a chromosome segment
from one chromosome to another non-homologous
chromosome
8-25

26. REFERENCE LIST
McCammon, W. (2008). Chapter 8 Cell Division and Reproduction.
http://www.slideshare.net/pisgahscience/08-lecture-ppt. Accessed : 18/03/2013.
Patterson, C. (2008). Cell Division Mitosis and Meiosis. http://www.slideshare.net/catherinepatterson/cell-
division-mitosis-and-meiosis-presentation. Accessed: 18/03/2013.
Scuffruff. (2008). Lesson 6a The Stages Of Meiosis. http://www.slideshare.net/scuffruff/lesson-6a-the-
stages-of-meiosis. Accessed: 18/03/2013
Sherif, S. (2011). http://www.slideshare.net/shimaasherif/cell-cycle-cell Cell cycle & cell division
by Shimaa Sherif on Feb 13, 2011-division. Accessed: 18/03/2013.
Swan, J. (2011). Chapter 13 (part 1) – Meiosis. http://www.slideshare.net/jayswan/chapter-13-part-1-
meiosis . Accessed : 18/03/2013
Wraithxjmin. (2008). Lecture 6 Cell Division [Meiosis]. http://www.slideshare.net/wraithxjmin/lecture-6-
cell-division-meiosis. Accessed: 18/03/12