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Chapters 47 & 21
Animal Development &
The Genetic Basis of Development
DEVELOPMENT
• An organism arises from a fertilized egg as the
result of three related processes
– Cell division
– Cell differentiation
– Morphogenesis
How does the ball
of cells know when
and where to
differentiate, fold
etc.?
Cytoplasmic
Determinants !
(usually maternal factors
like mRNA, proteins,
other chemicals)
They are
non-homogenous
Early Morphogenesis:
Gastrulation & Neurulation
Neurulation
video
http://www.yo
utube.com/wa
tch?v=ZeIyrInO
nMc
• Fertilization
• Gray crescent
• Establishing
the body axes
• What is
determination?
• What is
induction?
REGULATION OF GENE EXPRESSION
• Transcriptional regulation
is directed by:
TRANSCRIPTION FACTORS
such as:
– Maternal molecules in the
cell’s cytoplasm
(cytoplasmic determinants)
– Signals from other
cells (induction)
Drosophila melanogaster
• Each segment in the adult fly is anatomically
distinct
– And also has characteristic appendages… just like you?
HEAD
THORAX
ABDOMEN
Drosophila melanogaster
• Maternal cytoplasmic
determinants
– GRADIENTS of chemicals are
important
• Segmentation genes
– Gap genes
– Pair rule genes
– Segment polarity genes
–
–
–
http://www.youtube.com/watch?feature=endscreen&v=MefT
PoeVQ3w&NR=1
http://www.youtube.com/watch?v=uaedzlrnBGY
http://flymove.unimuenster.de/Processes/Segmentation/SegPair/SegPairEst/Seg
PairEstGes.html
HOMEOTIC GENES
• Master regulatory genes
• Specify the types of appendages and other
structures that each segment will form
• Mutations produce flies with structures in
incorrect places
Examples of Homeotic Mutations
Normal adult fly
Antennapedia
mutant
Bithorax mutant
Antennapedia Mutations
Wild-type
Mutants
HOMEOTIC GENES
• are master genes that
regulate the
expression of
numerous other
genes
– Some of the regulated
genes are regulatory
themselves
Drosophila DEVELOPMENT
REVIEW: Hierarchy of Gene Activity
• Maternal genes in cytoplasm of the egg
• Segmentation genes of embryo
– Gap genes
– Pair-rule genes
– Segment polarity genes
• Homeotic genes of the embryo
• Other genes of the embryo
HOMEOTIC GENES
• all possess homologous segments
– 180-nucleotide sequence = homeobox (HOX)
– Which encodes 60-amino-acid homeodomain
Homeodomain
• Homeotic genes
– encode for transcription factors
that influence other
developmental genes
– all have a hox region
(homeobox)
– which folds into a protein
called the homeodomain.
• Homeodomain is the DNA
Binding region of the
transcription factor
HOMEOTIC GENES
• Vertebrate genes
homologous to the
homeotic genes of
Drosophila have
maintained their
chromosomal
arrangement
• Ultrabithorax
• Other interesting
gene names in
Drosophila
http://jpetrie.myweb.uga.ed
u/genes.html
Regulatin’ Genes song for fun:
http://www.youtube.com/watch?
v=9k_oKK4Teco