2. Compare and contrase mitosis and
meiosis;
1
explain all the possible sources of
variation among daughter cells due to
meiosis and predict their impact on
genetic diversity; and
2
comapre and contrast spermatogenesis
and oogenesis.
3
Objectives
At the end of the session, you
should be able to:
5. It is the most common form
of cell division in somatic
eukaryotic cells (those that
will not become sex cells).
1 2
When mitosis is completed,
two genetically identical cells
are produced. It is a
fundamental process during
growth and tissue repair.
Mitosis
6. MITOSIS MEIOSIS
Mitosis is the process by which a
single cell divides into two identical
daughter cells. This type of division is
essential for growth and repair in
multicellular organisms, as well as for
asexual reproduction in some single-
celled organisms.
Meiosis is the process by which a
single cell divides into four daughter
cells, each with half the number of
chromosomes of the parent cell.
Meiosis is critical for sexual
reproduction, as it allows for the
production of gametes.
7.
8. MEIOSIS
Two divisions:
Meiosis I
Reduction Stage
Meiosis II
Equational Stage
Prophase I
Leptotone
Zygotene
Pachytene
Diplotene
Diakinesis
Prophase II
Metaphase II
Anaphase II
Telophase II
Metaphase I
Anaphase I
Telophase I
9. Chromosomes starts tobecome
visible & chromosomes ends
converge towards the centrosome
1
2
3
Prophase 1
Leptotene Stage
Zygotene Stage
chromosomes are joined together
(synapsis); sister chromatids closely joined
together with synaptonemal complex
Pachytene Stage
each chromosomes (bivalents) are
formed in pachynema; exchange/random
mixtures of genetic material
4Diplotene Stage
homologous chromosomes are
pulled apart in the chiasma
(where crossing-over occurred)
5 Diakinesis
further chromosomal takes place;
nuclear membrane breaks apart,
nucleolus disintegrate; & mitotic
spindle begins to form
11. Crossing-over
segment of one chromatid has changed
place with the equivalent segment of its
homologue
changed the content of the sister chromatids
these would be the ones ending up with the
parental types of chromosomes
12. Next phases..
ANAPHASE. homologous chromosomes are
completely separated and move towards
opposite poles.
METAPHASE. homologous pairs of
chromosomes align at the equatorial plate
TELOPHASE. cell divides into 2 daughter cells;
reformation of the nuclear envelope and
reappearance of nucleoli; reformation of the
nuclear envelope and reappearance of
nucleoli
13. MEIOSIS II
Cells that go into meiosis II do not undergo
DNA replication post-meiosis I
Events are essentially similar to mitosis but
there is no replication of chromosomes
resulting to four haploid cells, each with haf
as many chromosomes as the parent cell.
17. process by which
spermatozoa are formed in
the seminiferous tubules
it begins at puberty and
continue throughout life
Spermatogenesis
Spermiogenesis
maturation of spermatids to form
motile sperm capable of
penetrating the egg cell
18.
19. development of a mature
egg cell
primordial germ cells mostly
undergo atresia -
degeneration and resorption
of several follicles and their
ovules (a form of apoptosis)
prior to the maturation
Oogenesis
20.
21. Why is the process of meiosis essential to
sexual reproduction? What if gametes were
formed by mitotic rather than meiotic cell
division?
22. Reminders!
Monday (Oct. 16) - Loss of Cell Cycle Control in Cancer
Thursday (Oct. 19) - Formative Assessments (Meiosis & Loss
of Cell Cycle Control)
Monday (Oct. 23) - Long Test 2
