Download Chromosomes Chromosome

The Cell Cycle and How Cells Divide
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Review: Vocabulary - Chromosomes
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Chromosome: “spool” to hold DNA in the
nucleus
Homologous: pairs of chromosomes that
code for the same traits
Autosome: all chromosomes except X & Y
Sex Chromosomes: determine sex of
organisms – X & Y
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Review: Vocabulary - Cells
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Gametes: sex cells (egg/ovum and sperm)
Diploid – ( di = 2) having pairs of
chromosomes (all cells except gametes)
Haploid – (1/2) cells having only one of
each type of chromosome.
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Somatic Cells: all non-sex cells
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Zygote: the union of an ovum & sperm
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Review: What is DNA?
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The recipe for YOU! (genetic info)
Packaged into chromosomes
Figure 12.3
50 µm
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Review: Chromosomes
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Human cells have 46 chromosomes.
23 nearly-identical pairs (homologous)
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Review: Karyotype
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An ordered, visual representation of chromosomes
from a single organism.
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The Math: Chromosome = (n)
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n = the number of chromosomes in the
haploid cell
Egg (n) + sperm (n) = zygote (2n)
n + n = 2n
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)
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Math Practice
1.
1. egg = 23
n= _____ 2n = ____
2.
2. sperm = 4
n= ______ 2n = ____
3.
3. ovum = 12
n = _____ 2n = ____
4.
4. sperm = ___ n = 5
2n = ____
5.
5. ovum = ____ n = ____
2n = 20
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Homologues
• Homologous chromosomes:
• Look the same
• Control the same traits
• May code for different forms of each trait
• each one was inherited from a different
parent
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Review: Chromosome Duplication
In preparing for cell division, DNA is replicated and
the chromosomes condense
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Each duplicated chromosome has two
sister chromatids, attached at the centromere
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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.
0.5 µm
Chromosome
duplication
(including DNA
synthesis)
Centromere
Sister
Separation chromatids
of sister
chromatids
Centrometers
Sister chromatids
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Cell Cycle – Life Cycle of a cell
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Interphase – normal cell activity
Mitotic phase – cell divsion
INTERPHASE
Growth
G1
(DNA synthesis)
Growth
G2
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Phases of the Cell Cycle
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Interphase
– G1 - primary growth
– S – DNA repilcation
– G2 - secondary growth
M - mitosis
C - cytokinesis
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3 Purposes for Cell Division
100 µm
Reproduction.
200 µm
20 µm
Growth and
Tissue renewal
development.
or replacement
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Cell Division – Mitosis
(mi-to-sis)
“My two sis”(ter cells)
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Mitosis: produces identical cells
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The cell division process that forms two new
nuclei (cells); each of which has the same
number of chromosomes.
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Prophase – “prepare”
•chromosomes condense
Each duplicated chromosome
appears as two identical
sister chromatids joined
together.
PROPHASE
Early mitotic
spindle
Aster
Centromere
• The mitotic spindle begins
to form.
Chromosome, consisting
of two sister chromatids
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Metaphase:
“meet in middle”
•the longest stage of
mitosis, about 20 min.
METAPHASE
Metaphase
plate
• The centrosomes are at
opposite ends of the cell.
•The chromosomes meet in the
middle of the cell
Spindle
Centrosome at
one spindle pole
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Anaphase – “apart”
•shortest stage of mitosis,
lasting only a few minutes.
•each chromosome pair pulls
apart.
ANAPHASE
• Each chromatid becomes a fullfledged chromosome.
• By the end of anaphase, the
two ends of the cell have equal
and complete sets of
chromosomes.
Daughter
chromosomes
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Telophase – “tuck in”
• Two daughter nuclei begin
to form in the cell.
•The chromosomes
become less condensed.
• Mitosis, is now
complete.
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nucleolus
forming
Nuclear
envelope
forming
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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
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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
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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.
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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.
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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.
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Cytokinesis In Animal And Plant Cells
100 µm
Cleavage furrow
Contractile ring of
microfilaments
Vesicles
forming
cell plate
Wall of
patent cell
1 µm
Cell plate
New cell wall
Daughter cells
Daughter cells
(a) Cleavage of an animal cell (SEM)
(b) Cell plate formation in a plant cell (SEM)
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Cell Cycle and Mitosis 3-D Video
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http://www.youtube.com/watch?v=JcZQkmo
oyPk
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