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TWO TYPES OF CELL
DIVISION
Mitosis and
Meiosis
WHAT IS THE PURPOSE OF CELL DIVISION?
Growth
Repair
Replace
Reproduce
TWO T YPES OF REPRODUCTION
 Asexual by mitosis
One parent
Offspring identical to parent
Advantages?
Disadvantages?
Examples in:
Prokaryotes
Protist/Fungi
Plants
Sponges etc
SEXUAL REPRODUCTION
Process by which two cells (egg and sperm) from two parents join together to form one
cell (zygote) which then develops into the
offspring
Advantage
Variation
Disadvantage
Look for mates, loss of gametes, (energy
investment)
Chromosome number incompatibility!
HOW ARE CHROMOSOME NUMBERS MAINTAINED
FROM ONE GENERATION TO THE NEXT?
Activity
Each lab group;
1. One each of string of long red/yellow pop beads (20
beads each)
2. String of short red/yellow pop beads (10 beads each)
 Each lab table is one type of parent ex. Male or Female

 Fertilize the gametes – how many chromosomes? How
does that compare with the original chromosome
number?
CHROMOSOME NUMBERS:
All eukaryotic cells have pairs of chromosomes
where one of each pair are form each parent.
Haploid (N) = Half the number of
chromosomes in an eukaryotic cell. Usually
one of each pair
Diploid (2N) = total of number chromosomes in
an eukaryotic cell.
HOMOLOGOUS CHROMOSOMES
ID of Paired chromosomes
(homologous)
One from each parent
Same Centromere
position
Similar size
Similar genes or alleles
in the same locus
Stain the same
WHAT NEEDS TO HAPPEN BEFORE
FERTILIZATION?
Meiosis:
The egg/sperm cell will have N
chromosomes (or one of each pair).
Fertilization:
When egg and sperm unite – parental
chromosome number is restored (N + N
 2N)
How is meiosis different from mitosis?
CYCLE OF MEIOSIS AND FERTILIZATION
sporophyte
zygote
fertilization
diploid
haploid
meiosis
spores
gametes
gametophytes
Fig. 9-8a, p.146
multicelled
body
zygote
fertilization
diploid
haploid
meiosis
gametes
Fig. 9-8b, p.146
OVERVIEW OF MEIOSIS
PROPHASE I
Common to mitosis
Nuclear membrane disappears
Centrioles divide and migrate
to poles
Spindle fibers form
Different
Synapsis (homologous chrom.
come together
Called Tetrads
Crossing over
CROSSING OVER
 Segments between homologous chromosome are
exchanged (swapped)
 Results in new combinations of genes
MEIOSIS I
plasma
membrane
newly forming
microtubules in
the cytoplasm
PROPHASE I
spindle equator
(midway between the
two poles)
METAPHASE I
one pair of
homologous
chromosomes
ANAPHASE I
TELOPHASE I
Fig. 9-5a, p.142
MEIOSIS I CONT….
Metaphase I
Tetrads line up on the equator
Anaphase I
Homologous chromosomes separate and
go to the poles
Telophase I
Chromosomes may become diffuse and
nuclear membrane forms
Cytokinesis I
2 cells formed
MEIOSIS I
plasma
membrane
newly forming
microtubules in
the cytoplasm
PROPHASE I
spindle equator
(midway between the
two poles)
METAPHASE I
one pair of
homologous
chromosomes
ANAPHASE I
TELOPHASE I
Fig. 9-5a, p.142
Meiosis II
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
no
interphase
between
nuclear
divisions
Crossing over
occurs
between
homologues.
Homologous
pairs align
randomly.
Homologues
separate from
their partner.
typically
two
nuclei
(n)
Chromosomes
align at spindle
equator.
Sister chromatids four
of chromo-somes nuclei
seperate.
(4n)
Fig. 9-11b, p.148
MEIOSIS II
Prophase II: Chromosomes condense – have
the X shape
Metaphase II: Chromosomes line up on the
equator
Anaphase II: Centromeres split and
chromosomes migrate to the poles
Telophase II: Two nucleii form (cell plate or
cleavage furrow forms)
Cytokinesis: Two new cells form – each
containing _____ chromosomes
first polar
body
(haploid)
oogonium
(diploid
female
reproductive
cell)
three polar
bodies
(haploid)
primary oocyte
(diploid)
secondary
oocyte
(haploid)
ovum
(haploid)
a Growth
b Meiosis I and
cytoplasmic division
c Meiosis II and cytoplasmic
division
Fig. 9-10a, p.147
cell differentiation,
sperm formation
(mature, haploid
male gametes)
secondary
spermatocytes
(haploid)
spermatogonium
(diploid male
reproductive
cell)
a Growth
primary
spermatocyte
(diploid)
spermatids (haploid)
b Meiosis I and
cytoplasmic
division
c Meiosis II and
cytoplasmic division
Fig. 9-9, p.147
HOW DOES MEIOSIS PRODUCE VARIATION?
1.
Crossing over between homologous chromosomes
2. INDEPENDENT ASSORTMENT OF DIFFERENT
CHROMOSOMES DURING METAPHASE I
CHROMOSOMAL ABNORMALITIES
Turner’s Syndrome – Linda
Hunt
Nondisjunction of
homologous
chromosomes
Downs, Trisomy 21
Klinefelters, XXY
Turners Syndrome
XO
CHROMOSOMAL ABNORMALITIES
Klinefelter’s Karyotype
Down’s Syndrome
CHROMOSOMAL BREAKAGE DURING
CROSSING OVER THAT RESULTS IN SEGMENTS
OF CHROMOSOMES SHOWING ….