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Development
•Homework #2 is due
10/18
•Bonus #1 is due 10/25
•Weekly quiz online
each Thursday, due
each Tuesday
Developmental mutants of
Drosophila melanogaster
Fig 12.1
Vertebrate
Development:
from zygote to adult
Besides adding
cells, development
can involve cell
death.
Development of a mouse paw: yellow areas
show dying cells
CB 21.19
Early embryo development
Totipotent: ability to differentiate into any
cell-type
Totipotency is limited to early stages of animal
development
Why do cells lose totipotency?
Why do cells lose totipotency?
Mature,
differentiated plant
cells are totipotent
Why do cells lose totipotency?
•Gene expression can be
controlled at many points
between DNA and making
the final proteins.
•Changes in the various
steps of gene expression
control when and how
much of a product are
produced.
Why change gene expression?
•Different cells need different
components
•Responding to the
environment
•Replacement of
damaged/worn-out parts
DNA packaging
fluctuates…
genes being expressed
are unpackaged, genes
not needed are tightly
packaged.
Normally DNA is loosely
packaged
During mitosis DNA is tightly
packaged as chromosomes and
individually visible
box 2.1
DNA packaging
fluctuates…
Some of the tight
packaging of DNA is
irreversible.
Irreversible
packaging
of DNA
partially
explains the
loss of
totipotency.
Stem cells still have totipotency
Embryonic Stem Cells
are totipotent
Adult Stem Cells are
pluripotent (only form
some cell types)
Developmental information can be encoded by
both genetic and non-genetic information.
Fig 12.2
What genetic mechanisms regulate/allow
development?
All humans
are female for
the first nine
weeks of
development
All humans
are female for
the first nine
weeks of
development
Down’s Syndrome is caused
by an extra chromosome 21.
Down’s Syndrome is caused
by an extra chromosome 21.
Too much information disrupts
normal development.
4 whorls of a flower
Flower parts:
Complexity from a
few simple genes
Each whorl expresses a specific
combination of three genes
CB 21.20
Changing expression
of A, B, or C genes
changes organ identity
CB 21.20
Hox genes regulate the identity of
body parts
Fig 12.4
embryo
adult
Expression of hox genes
in the embryo give rise
to different adult body
parts.
Fig 12.4+.6
The order of Hox genes parallels the order of body
parts in which they are expressed
Fig 12.10
• Drosophila and vertebrate Hox protein show
striking similarities (500 million years since common ancestor)
Fig 12.9
• Many hox proteins have common sequences
(these are from Drosophila)
Fig 12.8
helix-turn-helix: a common DNA-binding motif
Fig 10.28+.29
Many developmental genes are transcription factors
Tbl 12.1
these are from Drosophila
Interaction of
genes can set
gradients in
cells/organisms
that signal how
different regions
should develop.
Fig 12.18
Reporter gene:
promoter
coding region
protein
promoter
reporter gene (luciferase, etc)
easily visualized protein
Fig 12.19
Interaction of
genes can set
gradients in
cells/organisms
that signal how
different regions
should develop.
Fig 12.18
Mutants in Drosophila embryo segment development
Fig 12.14
Gap genes affect formation of
continuous blocks of segments
Fig 12.14
Pair-rule genes
regulate pairing of
segments
Fig 12.14
Segment-polarity genes
regulate patterning of the
segments.
Fig 12.14
Hox genes regulate not segment patterns, but what
each segment will become
Fig 12.14
Why change gene expression?
•Different cells need different
components
•Responding to the
environment
•Replacement of
damaged/worn-out parts
Development
•Homework #2 is due
10/18
•Bonus #1 is due 10/25
•Weekly quiz online
each Thursday, due
each Tuesday