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