Download In eukaryotes, heritable information is passed to the next generation

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:
Think-Pair-Share
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How many cells are in your body?
How were those cells produced from a single cell called a
zygote?
How does the genetic information in one of your body cells
compare to that found in other body cells?
What are some advantages of asexual reproduction in
plants?
What is the importance of the fact that DNA is replicated
prior to cell division?
How do chromosomes move inside a cell during division?
How is the cell cycle controlled? What would happen if
the control were defective?
Why do cell divide?
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Reproduction – mitosis plays a role in asexual
reproduction
Growth
Repair
Mitosis followed by cytokinesis produces two
genetically identical daughter cells.
. Interphase consists of three phases: growth,
synthesis of DNA, preparation for mitosis.
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Mitosis alternates with interphase in the cell cycle.
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.
Mitosis
Mitosis passes a complete genome
from the parent cell to daughter cells.
Top 4 list to remember about mitosis:
 1. Mitosis occurs after DNA replication.
 2. Mitosis followed by cytokinesis produces two
genetically identical daughter cells.
 3. Mitosis plays a role in growth, repair, and
asexual reproduction
 4. Mitosis is a continuous process with observable
structural features along the mitotic process.
Replication  alignment  separation
Animal Mitosis
Binary Fission
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Bacteria may point
to the evolutionary
history of mitosis
The cell cycle is a complex set of stages that is highly
regulated with checkpoints, which determine the
ultimate fate of the cell.
The cell cycle is directed by internal controls or
checkpoints. Internal and external signals provide
stop-and-go signs at the checkpoints.
 examples:
• Mitosis-promoting factor (MPF)
• Action of platelet-derived growth factor (PDGF)
Cyclins and cyclin-dependent kinases control the cell
cycle.
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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.
How does meiosis and sexual
reproduction ensure genetic diversity?
Humans as an example:
#1 Random assortment of chromosomes
#2 Crossing Over
#3 Random Fertilization