Download Mitosis & Meiosis

8.2 Cells arise only from preexisting cells
• All cells come from cells
• Cellular reproduction is called cell division
– Cell division allows an embryo to develop into an
adult
– It also ensures the continuity of life from one
generation to the next
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Binary fission of a prokaryotic cell
Plasma
membrane
Prokaryotic
chromosome
Cell wall
Duplication of chromosome
and separation of copies
Continued growth of the cell
and movement of copies
Division into
two cells
Figure 8.3A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
8.5 The cell cycle multiplies cells
• The cell cycle consists of two major phases:
– Interphase, where chromosomes duplicate
and cell parts
are made
– The mitotic
phase, when
cell division
occurs
Figure 8.5
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Karyotype
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Before a cell starts
dividing, the
chromosomes are
duplicated
– This process
produces sister
chromatids
Sister chromatids
Centromere
Figure 8.4B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Chromosomes contain a very long DNA
molecule with thousands of genes
– Individual chromosomes are only visible
during cell division
– They are packaged as chromatin
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• When the cell
divides, the sister
chromatids separate
Chromosome
duplication
– Two daughter
cells are produced
– Each has a
complete and
identical set of
chromosomes
Sister
chromatids
Centromere
Chromosome
distribution
to
daughter
cells
Figure 8.4C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
8.6 Cell division is a continuum of dynamic
changes
• Cell Cycle:
• Interphase: G1, G0, S, G2
• Mitotic Phase: Mitosis / Cytokinesis
(Mitosis : PMAT)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Interphase
• G1 – cell grows / developes
• G0 – cell does what it normally supposed to do,
some cells stay in this phase forever, ex nerve
• S – DNA Replication
• G2 – organelles double, enzymes for cell
division made
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
INTERPHASE
PROPHASE
Centrosomes
(with centriole pairs)
Early mitotic
spindle
Centrosome
Chromatin
Nucleolus Nuclear
envelope
Plasma
membrane
Chromosome,
consisting of two
sister chromatids
Figure 8.6
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Fragments
of nuclear
envelope
Centrosome
Kinetochore
Spindle
microtubules
METAPHASE
ANAPHASE
Cleavage
furrow
Metaphase
plate
Spindle
TELOPHASE AND CYTOKINESIS
Daughter
chromosomes
Figure 8.6 (continued)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Nuclear
envelope
forming
Nucleolus
forming
8.7 Cytokinesis differs for plant and animal cells
• In animals, cytokinesis
occurs by cleavage
Cleavage
furrow
– This process pinches
the cell apart
Cleavage
furrow
Figure 8.7A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Contracting ring of
microfilaments
Daughter cells
• In plants, a
membranous cell
plate splits the cell in
two
Cell plate
forming
Wall of
parent cell
Cell wall
Figure 8.7B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Vesicles containing
cell wall material
Daughter
nucleus
New cell wall
Cell plate
Daughter
cells
8.10 Connection: Growing out of control, cancer
cells produce malignant tumors
• Cancer cells have abnormal cell cycles
– They divide excessively and can form abnormal
masses called tumors
• Radiation and chemotherapy are effective as
cancer treatments because they interfere with
cell division
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
MEIOSIS AND CROSSING OVER
8.12 Chromosomes are matched in homologous
pairs
• Homologous pairs –
chromosomes from
each parent that have
same genes but not
necessarily same
alleles
– Human cells have
46, making up 23
pairs of homologous
chromosomes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Chromosomes
Centromere
Sister chromatids
Figure 8.12
8.13 Gametes have a single set of chromosomes
• Diploid – somatic cells, 2 sets of chromosomes
• Haploid – gamete cells, 1 set chromosomes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• At fertilization, a sperm fuses with an egg,
forming a diploid zygote
– Repeated mitotic divisions lead to the
development of a mature adult
– The adult makes haploid gametes by meiosis
– All of these processes make up the sexual life
cycle of organisms
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The human
life cycle
Haploid gametes (n = 23)
Egg cell
Sperm cell
MEIOSIS
FERTILIZATION
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
Figure 8.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
8.14 Meiosis reduces the chromosome number
from diploid to haploid
• Meiosis, like mitosis, is preceded by
chromosome duplication
– However, in meiosis the cell divides twice to
form four daughter cells
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Meiosis I
- Homologous pairs separate
- During Prophase I, tetrads can cross over to
swap genetic info
- End with 2 Haploid cells with sister
chromatids
• Meiosis II
- sister chromatids separate
- end with 4 Haploid cells, no sister
chromatids
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
MEIOSIS I: Homologous chromosomes separate
INTERPHASE
Centrosomes
(with
centriole
pairs)
Nuclear
envelope
PROPHASE I
METAPHASE I
Microtubules
attached to
Spindle kinetochore
Sites of crossing over
Chromatin
Sister
chromatids
Tetrad
Figure 8.14, part 1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Metaphase
plate
Centromere
(with kinetochore)
ANAPHASE I
Sister chromatids
remain attached
Homologous
chromosomes separate
MEIOSIS II: Sister chromatids separate
TELOPHASE I
AND CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
AND CYTOKINESIS
Cleavage
furrow
Sister
chromatids
separate
Figure 8.14, part 2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Haploid
daughter cells
forming
Tetrad
Chaisma
Centromere
Figure 8.18A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Coat-color
genes
• How crossing over
leads to genetic
recombination
Eye-color
genes
Tetrad
(homologous pair of
chromosomes in synapsis)
1
Breakage of homologous chromatids
2
Joining of homologous chromatids
Chiasma
3
Separation of homologous
chromosomes at anaphase I
4
Separation of chromatids at
anaphase II and completion of meiosis
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Figure 8.18B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Gametes of four genetic types
8.15 Review: A comparison of mitosis and meiosis
• For both processes, chromosomes replicate only
once, during interphase
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
MITOSIS
MEIOSIS
PARENT CELL
(before chromosome replication)
Site of
crossing over
PROPHASE I
Tetrad formed
by synapsis of
homologous
chromosomes
PROPHASE
Duplicated
chromosome
(two sister chromatids)
METAPHASE
ANAPHASE
TELOPHASE
2n
Chromosome
replication
Chromosome
replication
2n = 4
Chromosomes
align at the
metaphase plate
Tetrads
align at the
metaphase plate
Sister chromatids
separate during
anaphase
Homologous
chromosomes
separate
during
anaphase I;
sister
chromatids
remain together
2n
Daughter cells
of mitosis
Figure 8.15
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
MEIOSIS I
METAPHASE I
ANAPHASE I
TELOPHASE I
Haploid
n=2
Daughter
cells of
meiosis I
No further
MEIOSIS II
chromosomal
replication; sister
chromatids
separate during
anaphase II
n
n
n
n
Daughter cells of meiosis II
• GENETIC VARIATION CAN RESULT FROM:
- crossing over
- homologous pairs rearranging
- random fertilization
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
POSSIBILITY 1
POSSIBILITY 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Gametes
Combination 1
Combination 2
Figure 8.16
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Combination 3
Combination 4
• Preparation of a karyotype
Blood
culture
Packed red
And white
blood cells
Hypotonic solution
Stain
White
Blood
cells
Centrifuge
3
2
1
Fixative
Fluid
Centromere
Sister
chromatids
Pair of homologous
chromosomes
4
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
5
Figure 8.19
8.20 Connection: An extra copy of chromosome 21
causes Down syndrome
• This karyotype shows three number 21
chromosomes
• An extra copy of chromosome 21 causes Down
syndrome
Figure 8.20A, B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
8.21 Accidents during meiosis can alter
chromosome number
• Abnormal
chromosome count
is a result of
nondisjunction
– Either
homologous
pairs fail to
separate
during
meiosis I
Nondisjunction
in meiosis I
Normal
meiosis II
Gametes
n+1
n+1
n–1
n–1
Number of chromosomes
Figure 8.21A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
– Or sister chromatids fail to separate during
meiosis II
Normal
meiosis I
Nondisjunction
in meiosis II
Gametes
n–1
n+1
n
Number of chromosomes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
n
Figure 8.21B
• Fertilization after nondisjunction in the mother
results in a zygote with an extra chromosome
Egg
cell
n+1
Zygote
2n + 1
Sperm
cell
n (normal)
Figure 8.21C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
8.22 Connection: Abnormal numbers of sex
chromosomes do not usually affect survival
• Nondisjunction can also produce gametes with
extra or missing sex chromosomes
– Unusual numbers of sex chromosomes upset the
genetic balance less than an unusual number of
autosomes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Table 8.22
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
SPERMATOGENESIS
– Spermatogenesis: the formation of sperm cells
• Diploid cells made continuously in
seminiferous tubules of testes
• Differentiated primary spermatocytes
• Haploid secondary spermatocytes
• Haploid sperm
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-04a
Epididymis
Testis
Scrotum
Penis
Diploid cell
2n
Differentiation and
onset of Meiosis I
2n
Primary spermatocyte
(in prophase of Meiosis I
Meiosis I completed
Cross section of
seminiferous
tubule
Secondary spermatocyte
(haploid; double chromatids)
n
n
Testis
Seminiferous tubule
Meiosis II
n
n
n
n
Developing sperm cells
(haploid; single chromatids)
Differentiation
n
n
n
n
Sperm cells
(haploid)
Center of
seminiferous tubule
LE 27-04b
Diploid cell
2n
In embryo
Differentiation and
onset of Meiosis I
Primary oocyte
2n
(arrested in prophase
of Meiosis I)
Present at birth
Completion of Meiosis I
and onset of Meiosis II
Secondary oocyte
(arrested at metaphase of Meiosis II;
released from ovary)
n
n
First
polar body
Entry of sperm triggers
completion of Meiosis II
Ovum
(haploid)
n
n
Second
polar body
Difference between Oogenesis and Spermatogenesis
• Oogenesis
• Spermatogenesis
- starts at birth /
primary oocyte arrested
in Prophase I
- starts at puberty
- puberty – release
secondary oocyte once a
month – STOPS after
eggs run out
- 4 haploid cells
- complete Meiosis II if
fertilized
- 1 egg, polar bodies
(unequal divisions)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
- division continuous