Download Ch. 47 2012

Chapter 47 : Animal Development
Terminology Review
• Development is determined by:
– zygote’s genome
– cytoplasmic determinants: molecules in the egg
• Cell differentiation: specialization of cells in structure
and function
• Morphogenesis: process by which an animal takes shape
• Model organisms: species representative of a larger
group and easily studied, ex. Drosophila, sea urchin, frog
Principles of differentiation:
1. Genomic Equivalence: our cells have the same genes,
but don’t have the same genes “on”
2. During early cleavage divisions, embryonic cells must
become different from one another
– If the egg’s cytoplasm is heterogenous, dividing cells vary
in the cytoplasmic determinants they contain
3. Induction: process where interactions among
embryonic cells influence their fate, via differential
gene expression and cell-cell communication
Fate Mapping
• Fate maps = territorial diagrams of embryonic
development
• Frog studies indicate cell lineage in germ layers
traces to blastula cells
• In many species that have cytoplasmic
determinants, only the zygote is totipotent
Fig. 47-21
Epidermis
Epidermis
Central
nervous
system
64-cell embryos
Notochord
Blastomeres
injected with dye
Mesoderm
Endoderm
Blastula
(a) Fate map of a frog embryo
Neural tube stage
(transverse section)
Larvae
(b) Cell lineage analysis in a tunicate
Formation of the Vertebrate Limbs
• Pattern formation: development of spatial organization
• Positional information: molecular cues that control
pattern formation
– Tells a cell where it is with respect to the body axes
Major limb-bud organizer regions
• Apical ectodermal ridge (AER): thickened area at bud
tip, allows outgrowth of the limb on the proper axes
• Zone of polarizing activity (ZPA): block of tissue that
organizes development of limb “sides” (i.e. littler
finger vs. thumb)
• Hox genes: “architect genes”
– Polysyndactyly (“many fingers joined together”) is a limb
disorder caused by a Hox mutation