Download Development and Genes

Agenda 3/24
• Development Quick Lecture
• Development Documentary and Notes
• Homework: Developmental Biology
Worksheet, Study for Unit Exam
• Turn in: Gene Expression Essay
• Warm Up: Summarize three major things
that occur during the development of
embryo to fetus.
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Development and Genes
What you need to know
• How we go from one unspecialized cell to
many specialized cells
– Determination
– Differentiation
– Morphogenesis
– Role of Mitosis and Gene Expression
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Characteristics of Development for Multicellular
Organisms
Development is the process of timed genetic controlled
changes that occurs in an organism’s life cycle.
• Mitosis
• Cell differentiation
• Pattern formation
• Morphogenesis
All four processes are anchored by differentiation with
regard to gene expression. Most cells in a multicellular
organism have the same genome or DNA. Genes must
be turned on and turned off during development.
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Cleavage (mitosis)
Cleavage is the time
of rapid mitosis
without significant
growth of daughter
cells. Cells become
increasing smaller.
Each cell is called a
blastomere. G1 and
G2 phases of cell
cycle is shortened or
eliminated.
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Gastrulation
After cleavage, development in animals is often
accompanied by mass movement of cells called
gastrulation.
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Cell, Genes and Development
Cells have two general classes of genes.
• Housekeeping genes which are necessary to go about the
“business” of life.
• For example genes that code for the enzymes for
cellular respiration are housekeeping genes. Most
cells have all of these activated
• Specialized genes that produce unique gene product
important to the cells differentiation.
•
For example the activation of the crystallin gene that
produces product necessary for the development of
the lens of the eye.
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Genes and
Development
It would be wasteful for
lens cells to produce
albumin, and in the
same way it would be
wasteful for the liver
cells to produce
crystallin. These
specialized genes must
be regulated so that
they are only activated
when they are needed
and timing is critical.
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Determination comes before Differentiation.
Determination are those things or processes necessary to
commit a cell to a particular type of cell or fate.
Differentiation is those changes that occur in a cell to
make it a certain cell type.
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Determination
Determination – Events that lead to the observable
differentiation of a cell. Once determination has
occurred then the final fate of the cell is sealed.
If a determined cell is placed in another location in the
organism, it will still differentiate into the cell that was
its normal fate.
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Determination
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How Determination Occurs
.
There are two sources responsible
for determining the fate or
development of cells.
• Cytoplasmic Determinants
• Induction via signals secreted by
neighboring cells
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Initial Development
Governed by Cytoplasmic
Determinants
Development can
begin with fertilization
of an egg and
subsequent division of
cytoplasmic
determinants during
cytokinesis. There is
unequal distribution
of the cytoplasmic
determinants to the
daughter cells as
illustrated.
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Initial Development Governed by
Once there are a multitude
of cells,
Inductive Signals
neighboring cells may produce signal
molecules that can
interact with receptor
sites and receiving
cells. This causes the
activation of a signal
transduction pathway
for the receiving cell.
This can send the cell
down a specific
developmental
pathway.
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Initial Development Governed by Cytoplasmic
Determinants
Cell Differentiation
• Differentiation of activated genes and inactive genes
• Appearance of mRNA for cell specific proteins
• Changes in cellular structure
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Morphogenesis
• How the organism gets it shape
• Hormones, cell signaling, and various
other stimuli can all affect morphogenesis
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Morphogenesis Can Involve Cell Death Occurs
Apoptosis occurs in the development of the digits of a
hand or paw. Shown is the development of a mouse paw.
The genes that regulate apoptosis are similar in both
vertebrates and invertebrates such as nematodes.
Fungi including yeast also have genes that regulate
apoptosis indicating these are ancient genes.
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During Development Cell Death Occurs
Apoptosis- Is a programed cell
death. Occurs in
• Infected cells
• Development
• Cells that are aged and no longer
functional
The cell below is a normal leukocyte
and the cell above is a cell
undergoing apoptosis
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What you need to know
• How we go from one unspecialized cell to
many specialized cells
– Determination
– Differentiation
– Morphogenesis
– Role of Mitosis and Gene Expression
– *Take notes on all the examples you see of
these in the film!
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