1. MONWABISI MKHIZE
201110525

MEIOSIS SLIDE PRESENTATION

2. Cell Division
MEIOSIS

3. Meiosis: Important Vocabulary

Diploid- contains 2
sets of chromosomes



(2n = 46)
Example: human
somatic cells
Haploid- contains 1 set
of chromosomes

(n = 23)

Example: human
gametes

4. Meiosis: Important
Vocabulary

Fertilization- fusion of two haploid gametes forms
a diploid zygote

Zygote- fertilized egg cell


The first cell of a new individual
What would happen if gametes were diploid?

5. Meiosis

Meiosis occurs in sexual reproduction when a diploid
germ cell produces four haploid daughter cells that
can mature to become gametes (sperm or egg).

6. Meiosis
Goal: reduce genetic material by half
Why?
n (mom) + n (dad) = 2n (offspring)
from mom
from dad
child
too
much!
meiosis reduces
genetic content
Just
right!

7. Meiosis: cell division in two parts
Sister
chromatids
separate
Chromatids
separate
Meiosis I
(reduction
division)
Meiosis II
(equational
division)
Diploid 2n
Diploid 2n
Haploid n
Result: one copy of each chromosome in a gamete.

8. Meiosis I : the reduction
division
Spindle
fibers
Nucleus
Prophase I
(early)
(diploid)
Prophase I
(late)
(diploid)
Metaphase I
(diploid)
Nuclear
envelope
Anaphase I
(diploid)
Telophase I
(diploid)

9. Prophase I
Late prophase
Early prophase
Chromatids pair.
Crossing over
occurs.
Chromosomes
condense.
Spindle forms.
Nuclear
envelope

10. Metaphase I
Chromatid pairs align
along the equator of the
cell.

11. Anaphase I
Chromosomes
separate and
move to opposite
poles.
Sister chromatids
remain
Attached at their
centromeres.

12. Telophase I
Nuclear envelopes
reassemble.
Spindle disappears.
Cytokinesis divides
cell into two.

13. Meiosis II
Gene X
Sister chromatids carry
identical genetic
information .
Meiosis II produces gametes with
one copy of each chromosome and thus
one copy of each gene.

14. Meiosis II : the equational
division
Prophase II
(diploid)
Metaphase II
Anaphase II
Telophase II
Four
Non-identical
haploid
daughter cells

15. Prophase II
Nuclear envelope
fragments.
Spindle forms.

16. Metaphase II
Chromosomes align
along equator of cell.

17. Anaphase II
Sister chromatids
separate
and move to opposite
poles.

18. Telophase II
Nuclear envelope
assembles.
Chromosomes
unravel.
Spindle disappears.
Cytokinesis divides
cell into two.

19. Results of meiosis
Four haploid
cells
•
One copy of
each
chromosome
•

20. What Meiosis is About
Meiosis allows the creation of unique individuals
through sexual reproduction.

21. Mitosis
Meiosis
Number of divisions
1
2
Number of daughter
cells
2
4
Yes
No
Same as parent
Half of parent
Where
Somatic cells
Sex cells
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction
Genetically
identical?
Chromosome #

22. MITOSIS
MEIOSIS
Occurs in somatic (body)
cells
Occurs only in gonads (sex
organs: ovary/testes)
Produces cells for repair,
maintenance, growth, asexual
reproduction
Only produces gametes (sex
cells: egg/sperm)
Results in identical diploid
(2n) daughter cells
Reduction division results in
4 haploid (n) cells

23. KARYOTYPE
1. Photograph a cell in metaphase.
2. Cut out the chromosomes from the picture.
3. Paste homologous pairs together
according to size, banding pattern and
centromere.

24. Karyotype is
used to
determine
1. If there is an
abnormality
in number or
structure of
the
chromosome
s
(eg. Down’s
syndrome)

25. •Karyotypes
of embryos are
obtained from:
CVS (chorionic villus sampling) and
amniocentesis.
•Karyotypes
of adults can be
obtained from any growing cells.
•Karyotypes
can not tell if there are
mutations of a gene.

26. Products of MITOSIS: 2 x 2n
cells.
2n
2n
2n
2 diploid cells
Products of MEIOSIS: 4 x n
cells
2n
n(4
n
n
monoploid cells)
n

27. MEIOSIS
is two mitotic divisions in a
row,
(meiosis I and II) except you will see
the homologous chromosomes coming
together . - -- in prophase I the double
homologous chromosomes come together to
form a tetrad
- Crossing-over (synapsis ) occurs in the
tetrad in prophase to increase the variability
in gametes.
- There is no dna replication in the interphase

29. Homologous
Chromosomes

Pair of chromosomes ( maternal and paternal) that
paternal
are similar in shape and size.

Homologous pairs (tetrads) carry genes
controlling the same inherited traits.

Each locus (position of a gene) is in the same
position on homologues.

Humans have 23 pairs of homologous
chromosomes.
a.
b.
22 pairs of autosomes
1 pair of sex chromosomes

30. Homologous
Chromosomes
eye color
locus
eye color
locus
hair color
locus
hair color
locus
Paternal
Maternal

31. Crossing Over (SYNAPSIS)
 Crossing over (variation) may
occur between
nonsister chromatids at the chiasmata.
chiasmata
 Crossing over:
over
segments of nonsister
chromatids break and reattach to the other
chromatid.
chromatid
 Chiasmata (chiasma) are
crossing over.
over
the sites of
Synapsis increases genetic variability –
and that’s a good thing…

32. Crossing Over - variation
nonsister chromatids
Tetrad
chiasmata: site
of crossing over
variation

33. Sex Chromosomes
XX chromosome - female
XY chromosome - male

34. Cytokinesis:
cytoplasm divides. Total
product is 4 cells, each with only a mom or Dad’s
chromosome, in other words, half the normal
chromosome number, or 4 monoploid (n) cells,
or 4 gametes.
Uneven cytokinesis in females: In
oogenesis, get one big egg and 3 nonfunctional polar bodies:
( who die off) and 1 big functional gamete

36. Spermatogene
sis
There are equal
divisions
producing four
equal sized
sperm.

37. Non-disjunction
= Nonseparatio
n of
chromoso
mes
resulting
in diploid
or empty
gametes.

38. Conditions caused by
non-disjunction
Downs syndrome = Trisomy 21 - 3 copies of
chromosomes 21 equalling a total of 47
chromosomes. = 2n + 1(chance of occurring in
oogenesis increases with maternal age)
Turners syndrome = Monosomy X - has only one
X chromosomes totalling only 45 chromosomes in
her body cells. (monosomy X)
= 2n-1
Klinefelter’s syndrome = XXY - male which has
an extra X chromosome = 2n + 1

39. Down’s syndrome – trisomy 21
A simple check for the
presence of a bone in the nose
could more accurately test
unborn babies for Down's
syndrome, scientists say.
Researchers say combining
the nose test with existing
screening methods
(amniocentesis, CVS) could
lead to a five-fold reduction in
the number of miscarriages
linked to an invasive
procedure used to confirm
Down's syndrome.

40. Klinefelter’s syndrome XXY
Normal boy who
develops some
female secondary
sex character-istics
at puberty.
-slightly lower IQ,
infertile, delayed
motor, speech,
maturation
-treated with
testosterone.

41. REFERENCES
Farrellw (2012) MEIO. ACCESS ON 7 MARCH 2014
http://www.slideshare.net/farrellw/meio-11234603
Docsawyer (2010) MEIOSIS. ACCESS ON 07 MARCH
2014
http://www.slideshare.net/docsawyer/meiosis-notes3075315