Warm-UP
1/6/16: SWBAT identify functions of cell
division.
1. Draw a cell and label as many parts as
you can. Take a full page for this one, you
will add to your picture as you can.
1
Quiz Corrections
You will have five minutes to change your
quiz. You may use your notes, but not your
neighbor. If you talk you will hand in your
quiz.
2
Phases of the Cell Cycle
•
The cell cycle consists of
– Interphase – normal cell activity
– The mitotic phase – cell divsion
INTERPHASE
Growth
G1
(DNA synthesis)
Growth
G2
3
Cell Division
•
•
•
An integral part of the cell cycle
Results in genetically identical daughter cells
Cells duplicate their genetic material
– Before they divide, ensuring that each daughter
cell receives an exact copy of the genetic
material, DNA
4
5
Functions of Cell Division
100 µm
(a) Reproduction.
An amoeba, a
single-celled
eukaryote, is
dividing into two
cells. Each new
cell will be an
individual
organism (LM).
200 µm
20 µm
(c) Tissue
renewal. These
dividing bone
This micrograph
marrow cells(arrow)
shows a sand dollar will give rise to new
embryo shortly after blood cells (LM).
the fertilized egg
divided, forming two
cells (LM).
(b) Growth and
development.
6
DNA can repair itself!!!
7
DNA
•
•
Genetic information = genome
Genetic information is packaged into
chromosomes
Figure 12.3
50 µm
8
DNA And Chromosomes
•
•
An average eukaryotic cell has about 1,000
times more DNA then an average
prokaryotic cell.
The DNA in a eukaryotic cell is organized
into several linear chromosomes, whose
organization is much more complex than the
single, circular DNA molecule in a
prokaryotic cell
9
Chromosomes
•
All eukaryotic cells store genetic information
in chromosomes.
– Most eukaryotes have between 10 and 50
chromosomes in their body cells.
– Human cells have 46 chromosomes.
– 23 nearly-identical pairs
10
Karyotype
•
•
•
An ordered, visual representation of the chromosomes in a cell
Chromosomes are photographed when they are highly condensed, then photos
of the individual chromosomes are arranged in order of decreasing size:
In humans each somatic cell has 46 chromosomes, made up of two sets, one
set of chromosomes comes from each parent
Pair of homologous
chromosomes
5 µm
Centromere
Sister
chromatids
11
Chromosomes
•
•
•
Non-homologous chromosomes
– Look different
– Control different traits
Sex chromosomes
– Are distinct from each other in their
characteristics
– Are represented as X and Y
– Determine the sex of the individual, XX being
female, XY being male
In a diploid cell, the chromosomes occur in pairs.
The 2 members of each pair are called
homologous chromosomes or homologues.
12
Chromosomes
•
•
•
A diploid cell has two sets of each of its chromosomes
A human has 46 chromosomes (2n = 46)
In a cell in which DNA synthesis has occurred all the chromosomes are
duplicated and thus each consists of two identical sister chromatids
Maternal set of
chromosomes (n = 3)
2n = 6
Paternal set of
chromosomes (n = 3)
Two sister chromatids
of one replicated
chromosome
Centromere
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
13
Homologues
• Homologous chromosomes:
• Look the same
• Control the same traits
• May code for different forms of each trait
• Independent origin - each one was inherited
from a different parent
14
Chromosome Duplication
•
•
In preparation for cell division, DNA is replicated and the chromosomes condense
Each duplicated chromosome has two sister chromatids, which separate during cell
division
0.5 µm
A eukaryotic cell has multiple
chromosomes, one of which is
represented here. Before
duplication, each chromosome
has a single DNA molecule.
Once duplicated, a chromosome
consists of two sister chromatids
connected at the centromere. Each
chromatid contains a copy of the
DNA molecule.
Mechanical processes separate
the sister chromatids into two
chromosomes and distribute
them to two daughter cells.
Chromosome
duplication
(including DNA
synthesis)
Centromere
Separation
of sister
chromatids
Sister
chromatids
15
Centrometers
Sister chromatids
Chromosome Duplication
•
•
Because of duplication, each condensed chromosome
consists of 2 identical chromatids joined by a centromere.
Each duplicated chromosome contains 2 identical DNA
molecules (unless a mutation occurred), one in each
chromatid:
Non-sister
chromatids
Centromere
Duplication
Sister
chromatids
Two unduplicated
chromosomes
Sister
chromatids
Two duplicated chromosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
16
Structure of Chromosomes
–
–
Diploid - A cell possessing two copies of each
chromosome (human body cells).
 Homologous chromosomes are made up of sister
chromatids joined at the centromere.
Haploid - A cell possessing a single copy of each
chromosome (human sex cells).
17
Warm-Up
1/7/16: SWBAT describe the difference
between cell division for sex cells (sperm and
eggs) and body cells (aka somatic cells, the
rest of the cells in your body).
What is one kind thing that you saw someone
else do for somebody this week.
18
Phases of the Cell Cycle
•
•
•
Interphase
–
G1 - primary growth
–
S - genome replicated
–
G2 - secondary growth
M - mitosis
C - cytokinesis
19
Mitosis



Some haploid & diploid cells divide by mitosis.
Each new cell receives one copy of every
chromosome that was present in the original cell.
Produces 2 new cells that are both genetically
identical to the original cell.
DNA duplication
during interphase
Mitosis
Diploid Cell
20
Mitotic Division of an Animal Cell
G2 OF INTERPHASE
Centrosomes
(with centriole pairs)
Nucleolus
Chromatin
(duplicated)
Nuclear
Plasma
envelope membrane
PROPHASE
Early mitotic
spindle
Aster
Centromere
Chromosome, consisting
of two sister chromatids
PROMETAPHASE
Fragments
of nuclear
envelope
Kinetochore
Nonkinetochore
microtubules
Kinetochore
microtubule
21
Mitotic Division of an Animal Cell
METAPHASE
ANAPHASE
Metaphase
plate
Spindle
Centrosome at Daughter
one spindle pole chromosomes
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nucleolus
forming
Nuclear
envelope
forming
22
Mitosis in a plant cell
Chromatine
Nucleus
Nucleolus condensing
1 Prophase.
The chromatin
is condensing.
The nucleolus is
beginning to
disappear.
Although not
yet visible
in the micrograph,
the mitotic spindle is
staring to from.
Chromosome
Metaphase. The
2 Prometaphase.
3
4
spindle is complete,
We now see discrete
and the chromosomes,
chromosomes; each
attached to microtubules
consists of two
at their kinetochores,
identical sister
are all at the metaphase
chromatids. Later
plate.
in prometaphase, the
nuclear envelop will
fragment.
5
Anaphase. The
chromatids of each
chromosome have
separated, and the
daughter chromosomes
are moving to the ends
of cell as their
kinetochore
microtubles shorten.
Telophase. Daughter
nuclei are forming.
Meanwhile, cytokinesis
has started: The cell
plate, which will
divided the cytoplasm
in two, is growing
toward the perimeter
of the parent cell.
23
24
Meiosis and Sexual Life Cycles
•
•
•
Living organisms are distinguished by their ability to
reproduce their own kind
Heredity
– Is the transmission of traits from one generation to the
next
Variation
– Shows that offspring differ somewhat in appearance
from parents and siblings
25
Inheritance of Genes
•
•
•
Genes are segments of DNA, units
of heredity
Offspring acquire genes from
parents by inheriting
chromosomes
Genetics is the scientific study of
heredity and hereditary variation
26
Inheritance of Genes
•
•
•
Each gene in an organism’s DNA has a
specific locus on a certain chromosome
We inherit one set of chromosomes from our
mother and one set from our father
Two parents give rise to offspring that have
unique combinations of genes inherited from
the two parents - sexual reproduction
27
Sexual Reproduction
•
•
Fertilization and meiosis alternate in sexual life cycles
A life cycle is the generation-to-generation sequence of
stages in the reproductive history of an organism
Key
Haploid
Diploid
n
n
Gametes
n
MEIOSIS
FERTILIZATION
Zygote
2n
Diploid
multicellular
organism
2n
Mitosis
(a) Animals
28
Sex Cells - Gametes
•
•
Unlike somatic cells, sperm and egg cells
are haploid cells, containing only one set of
chromosomes
At sexual maturity the ovaries and testes
produce haploid gametes by meiosis
29
Meiosis
•
•
Reduces the chromosome number such that
each daughter Cell has a haploid set of
chromosomes
Ensures that the next generation will have:
– Diploid number of chromosome
– Exchange of genetic information
(combination of traits that differs from that
of either parent)
30
•
•
•
•
Meiosis
Only diploid cells can divide
by meiosis.
Prior to meiosis I, DNA replication occurs.
During meiosis, there will be two nuclear
divisions, and the result will be four haploid
nuclei.
No replication of DNA occurs between
meiosis I and meiosis II.
31
Meiosis
Interphase
•
•
Meiosis reduces the
number of chromosome
sets from diploid to
haploid
Meiosis takes place in
two sets of divisions
–
–
Meiosis I reduces the
number of chromosomes
from diploid to haploid
Meiosis II produces four
haploid daughter cells
Figure 13.7
Homologous pair
of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids
Diploid cell with
replicated
chromosomes
Meiosis I
1 Homologous
chromosomes
separate
Haploid cells with
replicated chromosomes
Meiosis II
2 Sister chromatids
separate
Haploid cells with unreplicated chromosomes
32
Meiosis Phases
•
•
•
•
Meiosis involves the same four phases seen in
mitosis
 prophase
 metaphase
 anaphase
 telophase
They are repeated during both meiosis I and
meiosis II.
The period of time between meiosis I and meiosis
II is called interkinesis.
No replication of DNA occurs during interkinesis
because the DNA is already duplicated.
33
Prophase I
•
•
•
•
•
Prophase I occupies more than 90% of the time required for meiosis
Chromosomes begin to condense
In synapsis, the 2 members of each homologous pair of chromosomes
line up side-by-side, aligned gene by gene, to form a tetrad consisting
of 4 chromatids
During synapsis, sometimes there is an exchange of homologous parts
between non-sister chromatids. This exchange is called crossing over
Each tetrad usually has one or more chiasmata, X-shaped regions
where crossing over occurred
Nonsister
chromatids
Prophase I
of meiosis
Tetrad
Chiasma,
site of
crossing
over
34
Metaphase I
•
•
•
At metaphase I, tetrads line up at the metaphase plate, with one
chromosome facing each pole
Microtubules from one pole are attached to the kinetochore of one
chromosome of each tetrad
Microtubules from the other pole are attached to the kinetochore of the
other chromosome
PROPHASE I
Sister
chromatids
Tetrad
METAPHASE I
ANAPHASE I
Sister chromatids
remain attached
Centromere
(with kinetochore)
Chiasmata
Metaphase
plate
Spindle
Microtubule
attached to
kinetochore
Homologous chromosomes
(red and blue) pair and
exchange segments; 2n = 6
Homologous
chromosomes
separate
Tetrads line up
Pairs of homologous
chromosomes split up
35
Anaphase I
•
•
•
In anaphase I, pairs of homologous chromosomes separate
One chromosome moves toward each pole, guided by the
spindle apparatus
Sister chromatids remain attached at the centromere and
move as one unit toward the pole
PROPHASE I
Sister
chromatids
Tetrad
METAPHASE I
ANAPHASE I
Sister chromatids
remain attached
Centromere
(with kinetochore)
Chiasmata
Metaphase
plate
Spindle
Microtubule
attached to
kinetochore
Homologous chromosomes
(red and blue) pair and
exchange segments; 2n = 6
Homologous
chromosomes
separate
Tetrads line up
Pairs of homologous
chromosomes split up
36
Telophase I and Cytokinesis
•
•
•
•
In the beginning of telophase I, each half of the
cell has a haploid set of chromosomes; each
chromosome still consists of two sister chromatids
Cytokinesis usually occurs simultaneously,
forming two haploid daughter cells
In animal cells, a cleavage furrow forms; in plant
cells, a cell plate forms
No chromosome replication occurs between the
end of meiosis I and the beginning of meiosis II
because the chromosomes are already replicated
37
Prophase II
•
•
•
Meiosis II is very similar to mitosis
In prophase II, a spindle apparatus forms
In late prophase II, chromosomes (each still composed of
two chromatids) move toward the metaphase plate
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
Cleavage
furrow
METAPHASE II
ANAPHASE II
Sister chromatids
separate
TELOPHASE II AND
CYTOKINESIS
Haploid daughter cells
forming
38
Metaphase II
•
•
•
At metaphase II, the sister chromatids are at the metaphase plate
Because of crossing over in meiosis I, the two sister chromatids of each
chromosome are no longer genetically identical
The kinetochores of sister chromatids attach to microtubules extending
from opposite poles
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
Cleavage
furrow
METAPHASE II
ANAPHASE II
Sister chromatids
separate
TELOPHASE II AND
CYTOKINESIS
Haploid daughter cells
forming
39
Anaphase II
•
•
At anaphase II, the sister chromatids separate
The sister chromatids of each chromosome now move as
two newly individual chromosomes toward opposite poles
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
Cleavage
furrow
METAPHASE II
ANAPHASE II
Sister chromatids
separate
TELOPHASE II AND
CYTOKINESIS
Haploid daughter cells
forming
40
Telophase II and Cytokinesis
•
•
•
•
•
In telophase II, the chromosomes arrive at opposite poles
Nuclei form, and the chromosomes begin decondensing
Cytokinesis separates the cytoplasm
At the end of meiosis, there are four daughter cells, each with a haploid
set of unreplicated chromosomes
Each daughter cell is genetically distinct from the others and from the
parent cell
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
Cleavage
furrow
METAPHASE II
ANAPHASE II
Sister chromatids
separate
TELOPHASE II AND
CYTOKINESIS
Haploid daughter cells
forming
41
Definition of Recombination
or Genetic Recombination or Crossing
Over
•
Breaking and rejoining of two parental DNA
molecules to produce new DNA molecules
42
Meiotic recombination
•
Recombination appears to be needed to keep maternal
and paternal homologs of chromosomes together prior to
anaphase of meiosis I
–
–
–
–
•
•
Zygotene: Pairing of maternal and paternal chromosomes (each has 2
sister chromatids)
Pachytene: Crossing over between maternal and paternal chromosomes
Diplotene: Centromeres of maternal and paternal chromosomes separate,
but chromosomes are held together at chiasmata (cross-overs)
Anaphase I: Homologous chromosomes separate and move to 2 daughter
cells.
Results in >1 exchange between pairs of homologous
chromosomes in each meiosis.
Failure to keep homologous chromosomes together prior to
anaphase I can lead to aberrant numbers of chromosomes,
e.g. trisomy for chromosomes 15, 18, 21
43
Cross-overs during meiosis I
Zygotene: Homologous
Maternal
Paternal
chromosomes,
each with 2 sister chromatids, pair to
form bivalents (line=duplex DNA)
Pachytene: Cross-overs between
homologous chromosomes
Diplotene: homologous chromosomes
separate partially but are held together at
cross-overs
Metaphase I
Anaphase I
Anaphase I: Cross-overs resolve to
allow homologous chromosomes to
separate into separate cells
Meiosis II
44
Benefits of recombination
•
•
•
Greater variety in offspring: Generates
new combinations of alleles
Negative selection can remove
deleterious alleles from a population
without removing the entire
chromosome carrying that allele
Essential to the physical process of
meiosis, and hence sexual reproduction
45
A Comparison of Mitosis and Meiosis
•
•
•
Mitosis conserves the number of chromosome
sets, producing cells that are genetically identical
to the parent cell
Meiosis reduces the number of chromosomes sets
from two (diploid) to one (haploid), producing cells
that differ genetically from each other and from the
parent cell
The mechanism for separating sister chromatids is
virtually identical in meiosis II and mitosis
46
A Comparison Of Mitosis And Meiosis
MITOSIS
MEIOSIS
Chiasma (site of
crossing over)
Parent cell
(before chromosome replication)
MEIOSIS I
Prophase I
Prophase
Chromosome
replication
Duplicated chromosome
(two sister chromatids)
Chromosome
replication
Tetrad formed by
synapsis of homologous
chromosomes
2n = 6
Chromosomes
positioned at the
metaphase plate
Metaphase
Sister chromatids
separate during
anaphase
Anaphase
Telophase
2n
Tetrads
positioned at the
metaphase plate
Homologues
separate
during
anaphase I;
sister
chromatids
remain together
Metaphase I
Anaphase I
Telophase I
Haploid
n=3
Daughter
cells of
meiosis I
2n
MEIOSIS II
Daughter cells
of mitosis
n
n
n
n
Daughter cells of meiosis II
Sister chromatids separate during anaphase II
47
Comparison
•
•
•
•
•
•
Meiosis
DNA duplication
followed by 2 cell
divisions
Sysnapsis
Crossing-over
One diploid cell
produces 4
haploid cells
Each new cell
has a unique
combination of
genes
•
•
•
•
•
Mitosis
Homologous
chromosomes do not
pair up
No genetic exchange
between homologous
chromosomes
One diploid cell
produces 2 diploid
cells or one haploid
cell produces 2
haploid cells
New cells are
genetically identical to
original cell (except for
mutation)
48
Asexual Reproduction
•
In asexual reproduction, one parent
produces genetically identical offspring by
mitosis
Parent
Bud
Figure 13.2
0.5 mm
49
Cool -Down
Please write a summary of what you have
learned about cells so far specifically, how
they function and how they divide. Compare
and contrast wherever possible. (for
example: prokaryote v eukaryote, meiosis v
mitosis, animal v plant)
50