Download In eukaryotes, heritable information is passed to the

IN EUKARYOTES, HERITABLE
INFORMATION IS PASSED TO THE NEXT
GENERATION VIA PROCESSES THAT
INCLUDE THE CELL CYCLE AND MITOSIS
OR MEIOSIS PLUS FERTILIZATION.
Essential knowledge 3.A.2:
What are the key roles of cell division?
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Reproduction – mitosis plays a role in asexual
reproduction
Growth
Repair
Mitosis followed by cytokinesis produces two
genetically identical daughter cells.
Chromosome Structure
What is the
difference
between
chromatin,
chromatids,
chromosome,
DNA, Genes
Has anyone ever
seen a gene?
Can we see the
impact of a
gene?
Cell Division
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Distributes identical sets of chromosomes to
daughter cells
Genome – the total hereditary endowment of a cell
(Amount varies in organisms)
Human Genome Project
Exists in two steps: Mitosis (nuclear division) and
Cytokinesis (Cell division)
Cell Cycle
Cell Specialization
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When a cell specializes, it often enters into a stage
where it no longer divides, but it can reenter the cell
cycle when given appropriate cues.
Nondividing cells may exit the cell cycle; or hold at
a particular stage in the cell cycle.
Animal Mitosis
Cytokinesis: Plants Vs. Animals
Binary Fission
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Bacteria may point
to the evolutionary
history of mitosis
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a. The cell cycle is a complex set of stages that is highly
regulated with checkpoints, which determine the
ultimate fate of the cell.
2. The cell cycle is directed by internal controls or
checkpoints. Internal and external signals provide stopand-go signs at the checkpoints.
To foster student understanding of this concept, instructors
can choose an illustrative example such as:
• Mitosis-promoting factor (MPF)
• Action of platelet-derived growth factor (PDGF)
• Cancer results from disruptions in cell cycle control
Control Systems
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The distinct events of the
cell cycle are directed
by a distinct cell cycle
control system.
A checkpoint in the cell
cycle is a critical control
point where stop and go
signals regulate the
cycle.
Three major checkpoints
are found in the G1, G2,
and M phases.
Control Systems
 Rhythmic fluctuations in the
abundance and activity of
control molecules pace the
cell cycle.
 Some molecules are protein
kinases that activate or
deactivate other proteins by
phosphorylating them.
 The levels of these kinases
are present in constant
amounts, but these kinases
require a second protein, a
cyclin, to become activated.
 Levels of cyclin proteins
fluctuate cyclically.
 The complex of kinases and
cyclin forms cyclindependent kinases (Cdks).
Cancer cells have escaped from cell
cycle control
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Cancer cells do not stop dividing when growth factors
are depleted either because they manufacture their
own, have an abnormality in the signaling pathway,
or have a problem in the cell cycle control system.
If and when cancer cells stop dividing, they do so at
random points, not at the normal checkpoints in the
cell cycle.
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The abnormal behavior of cancer cells begins when a
single cell in a tissue undergoes a transformation that
converts it from a normal cell to a cancer cell.
Normally, the immune system recognizes and destroys
transformed cells.
However, cells that evade destruction proliferate to
form a tumor, a mass of abnormal cells.
Meiosis
Quick Comparison
Mitosis
After cell division the
daughter cell are
genetically the same as
the parent cell. They
have basically cloned
themselves.
The chromosome numbers
are also the same.
2n to 2n
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Meiosis
After cell division the
daughter cells are
genetically different
than the parent cell.
The cell divides twice.
The daughter cell have
half the number of
chromosomes as the
parent.
2n to 1n
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What makes meiosis different?
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During meiosis, homologous
chromosomes are paired,
with one homologue
originating from the
maternal parent and the
other from the paternal
parent.
Orientation of the
chromosome pairs is random
with respect to the cell poles.
Separation of the
homologous chromosomes
ensures that each gamete
receives a haploid (1n) set
of chromosomes composed
of both maternal and
paternal chromosomes.
Crossing Over
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During meiosis, homologous chromatids exchange
genetic material via a process called “crossing
over,” which increases genetic variation in the
resultant gametes.
Crossing over helps ensure genetically different
offpsring
Meiosis forms haploid sperm and egg
Fertilization
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Fertilization involves the fusion of two gametes,
increases genetic variation in populations by
providing for new combinations of genetic
information in the zygote, and restores the diploid
number of chromosomes.