Post on 05-Jan-2016
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.youtube.com/watch?v=ZeIyrInOnMc
• Fertilization• Gray crescent• Establishing
the body axes
• What is determination?
• What is induction?
REGULATION OF GENE EXPRESSION• Transcriptional regulation
is directed by:
TRANSCRIPTION FACTORSsuch 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=MefTPoeVQ3w&NR=1
– http://www.youtube.com/watch?v=uaedzlrnBGY – http://
flymove.uni-muenster.de/Processes/Segmentation/SegPair/SegPairEst/SegPairEstGes.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.edu/genes.html
Regulatin’ Genes song for fun: http://www.youtube.com/watch?v=9k_oKK4Teco