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 utube.com/wa tch?v=ZeIyrInO nMc 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 – PoeVQ3w&NR=1 PoeVQ3w&NR=1 – – muenster.de/Processes/Segmentation/SegPair/SegPairEst/Seg PairEstGes.html muenster.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 u/genes.html u/genes.html Regulatin’ Genes song for fun: v=9k_oKK4Teco v=9k_oKK4Teco