1. SEXUAL REPRODUCTION AND
GENETICS MEIOSIS

2.  In humans, somatic cells (body cells) have:
 23 pairs of homologous chromosomes and
 one member of each pair from each parent.
 The human sex chromosomes (Gonosomes)
X and Y differ in size and genetic composition.
 The other 22 pairs of chromosomes are
autosomes with the same size and genetic
composition.
© 2012 Pearson Education, Inc.

3. Homologous chromosomes are
matched in:
• length,
 centromere position, and
 gene locations (locus).
 A locus is the position of a gene.
 Different versions alleles of a gene may be
found at the same locus on maternal and
paternal chromosomes.
© 2012 Pearson Education, Inc.

4. Fig. 13-3b
TECHNIQUE
5 µm
Pair of homologous
replicated chromosomes
Centromere
Sister
chromatids
Metaphase
chromosome

5.  All
organisms have
different numbers of
chromosomes.
 A body cell in an adult
fruit fly has 8
chromosomes: 4 from
the fruit fly's male
parent, and 4 from its
female parent.

6. These
two sets of chromosomes
are homologous.
Each of the 4 chromosomes that
came from the paternal has a
corresponding chromosome from
the maternal

7. A cell that contains both sets of
homologous chromosomes is said to
be diploid.
The number of chromosomes in a
diploid cell is sometimes represented
by the symbol (2n)

8.  Meiosis is a process that converts diploid
nuclei to haploid nuclei.
 Diploid cells have 2 sets of
chromosomes.
 Haploid cells have 1 set of
chromosomes.
 Meiosis occurs in the sex organs,
producing gametes—sperm and eggs.
 Fertilization is the fusion of a sperm and egg
cell.
 The zygote has a diploid chromosome
number, one set from each parent.
© 2012 Pearson Education, Inc.

9. What
happens during the process of
meiosis?

10. Meiosis
involves two divisions,
meiosis I and meiosis II.
By the end of meiosis II, the diploid
cell that entered meiosis has become
4 haploid cells.

11. Meiosis
Interphase I
I
Prophase I
Metaphase I
Anaphase I
Telophase I
and
Cytokinesis

12. Interphase I
Cells
undergo a
round of DNA
replication,
forming duplicate
chromosomes.

13. MEIOSIS I:
Prophase I
 Each
chromosome
pairs with its
corresponding
homologous
chromosome to
form a tetrad.
 There are 4
chromatids in a
tetrad.

14. When
homologous chromosomes form
tetrads in meiosis I, they exchange
portions of their chromatids in a process
called crossing over.
Crossing-over produces new
combinations of alleles.

15. MEIOSIS I:
Metaphase I
Spindle fibers
attach to the
chromosomes.

16. MEIOSIS I:
Anaphase I
The
fibers pull
the homologous
chromosomes
toward opposite
ends of the cell.

17.  Nuclear
MEIOSIS I:
Telophase I and
Cytokinesis
membranes form.
 The cell separates into two
cells.
 The two cells produced by
meiosis I have
chromosomes and alleles
that are different from each
other and from the diploid
cell that entered meiosis I.

18. MEIOSIS ll
The
two cells produced by meiosis I
now enter a second meiotic division.
Unlike meiosis I, neither cell goes
through chromosome replication.
Each of the cell’s chromosomes has 2
chromatids.

19. Meiosis II
Telophase I and
Cytokinesis I
Meiosis II
Prophase II
Metaphase II
Anaphase II Telophase II
and
Cytokinesis

20. MEIOSIS II:
Prophase II
Meiosis
I results
in two haploid (n)
daughter cells,
each with half the
number of
chromosomes as
the original cell.

21. MEIOSIS II
Metaphase II
The
chromosomes
line up in the
center of cell.

22. MEIOSIS II
Anaphase II
 The
sister
chromatids
separate and move
toward opposite
ends of the cell.

23. MEIOSIS II
Telophase II and Cytokinesis
 Meiosis
II results in
four haploid (n)
daughter cells
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of%20Meiosis

24. In
male animals, meiosis results in
four equal-sized gametes called
sperm.

25. In
many female animals, only one egg
results from meiosis.
The other three cells, called polar
bodies, are usually not involved in
reproduction.

26. MITOSIS
• Cells produced by mitosis have the
same number of chromosomes and
alleles as the original cell.
• Mitosis allows an organism to grow
and replace cells.
• Some organisms
reproduce asexually by mitosis.

27. MEIOSIS
Cells produced by meiosis have half the
number of chromosomes as the parent
cell.
These cells are genetically different from
the diploid cell and from each other.
Meiosis is how sexually-reproducing
organisms produce gametes.

28.  Cayey,C.U (2013), The Cycle. http://www.slideshare.net/caecayey/cap-12-ciclocelular
 Feder, A. (2013). http://www.slideshare.net/jojatk/meiosisglencoe?qid=62b29050-df7e-4e20-a3589aec8af199ae&v=qf1&b=&from_search=12
 Gquinnn617,(2014), Median Genetics and meiosis.
http://www.slideshare.net/gquinn617/09-genetics?qid=62b29050-df7e-4e20a358-9aec8af199ae&v=qf1&b=&from_search=6
 Rozeka, P. (2013). Biology, cell division meiosis.
http://www.slideshare.net/rozeka01/biology-unit-4-cell-division-meiosisnotes?qid=62b29050-df7e-4e20-a3589aec8af199ae&v=qf1&b=&from_search=10
Swan,J. (2011). Meiosis and Sexual Life Cycle.
http://www.slideshare.net/jayswan/chapter-12-presentation-6504580