01-Questions.pdf

Questions and Approaches definitions the questions of developmental biology approaches to developmental biology o comparative embryology o evolutionary embryology o medical embryology & teratology 13th ed. References: Chapt 1 p. 1-5; 16; 2...

Questions and Approaches definitions the questions of developmental biology approaches to developmental biology o comparative embryology o evolutionary embryology o medical embryology & teratology 13th ed. References: Chapt 1 p. 1-5; 16; 21-26 (12th ed. References: Chapt 1 p. 1-5; 18; 25-30, 37)  Definitions Embryology: the study of development between fertilization and birth (traditional definition). zygote (fertilized egg) => developed adult body Developmental biology: the study of all developmental processes throughout the life of the organism; from fertilization to death.  Questions of developmental biology 1) Differentiation: the generation of specialized cell types from undifferentiated precursors. How are the different cell types generated? zygote multicellular organism ===============> (one cell) with many cell types  Questions of developmental biology 2) Morphogenesis: the organization of cells into ordered and predictable structures. What factors direct the formation of ordered structures? cells ==============> specific tissues and organs at specific sites  Questions of developmental biology 3) Growth: controlled cell division and proliferation. How is cell division regulated? differentiated organized =============> cells structures limited # of cell divisions If abnormal # of cell divisions: => malformations or disruptions  Amphibian development Ectodermal Mesodermal Endodermal Germ derivatives derivatives derivatives line  Major cell lines Germ cells: produce gametes contain the genetic material passed to the next generation Somatic cells: form the body of the organism all cells other than the germline  Questions of developmental biology 4) Reproduction: the production of new individuals → the production of new organisms similar in form to their parents ensures the continuity of life → germline: generates gametes (egg/sperm) that transmit genetic information How is the germ line set aside?  Questions of developmental biology 5) Evolution: results from the accumulation of inherited modifications of developmental programs. → the generation of new species How are new body forms generated?  Questions of developmental biology 6) Environmental integration: the induction of development by environmental cues. How is development influenced by the environment of the organism? environment/non-genetic factors zygote ========> development genes Example: identical twins. identical genetic information but appearance may differ, presumably because of non-genetic factors Environmental integration Approaches to the study of developmental biology Three categories: anatomical experimental genetic  Anatomical approaches Comparative embryology: studies how the anatomy of the embryo changes during development in different organisms. Evolutionary embryology: studies how variations in developmental patterns account for evolutionary change. Medical embryology & Teratology: the study of birth defects (genetic or induced), and what can abnormalities tell us about the normal process of development. Comparing vertebrate embryos  Evolutionary embryology: accumulation of genetic changes Dachshunds: short legs are caused by a duplication of the Fgf4 (fibroblast growth factor 4) gene, which signals cartilage precursors cells to stop dividing and begin differentiation Long-haired dachshund: longer hair is caused by an additional change: a mutation in the Fgf5 gene, which is involved in hair production  Selection of genetic changes in dachshunds  Evolutionary embryology: taxonomic classification The use of larval forms for taxonomic classification: relationships between groups of organisms have been established by finding common embryonic or larval forms. Example: barnacles barnacles were originally classified as molluscs based on adult morphology in the 1830s, J. V. Thompson (English zoologist) observed that larval barnacles were very similar to larval shrimp and proposed (correctly) that barnacles should be classified as arthropods Barnacles  Embryonic homologies Homologous structures are organs that have similar functions because they are derived from a common ancestral structure. examples: vertebrate forelimbs This similarity is different from that between analogous structures, which perform similar functions but do not arise from a common ancestor (example: the wings of insects and birds) Embryonic homologues: vertebrate forelimbs  Evolutionary change is based on developmental change Homologous anatomical structures differentiate by altering development. Example: the bat wing is made in part by: 1) maintaining a rapid growth rate in the cartilage that forms the fingers (digits: I-V) 2) preventing cell death in the webbing between the fingers (arrow: the cell death occurring in mice and humans results in free digits) Evolutionary change is based on developmental change Evolutionary change is based on developmental change  Medical embryology: the study of malformations Malformations are abnormalities caused by genetic events (gene mutations and chromosomal defects). Piebaldism is caused by a mutation in kit, a gene that normally enables certain cell types to proliferate & migrate. Affected cell types: neural crest cells (the precursors of pigment cells, some ear cells, and gut neurons responsible for peristalsis) => underpigmentation, deafness, and gut malformations blood cell precursors => anemia germ cell precursors => sterility Piebaldism feature of Waardenburg syndrome Magpie Bald Eagle  Receptor Tyrosine Kinases RTK  Medical embryology: Piebaldism A mouse model displays the same syndrome as humans and can be used for developmental studies.  Teratology: the study of disruptions Disruptions are abnormalities caused by exogenous agents = teratogens: chemicals, radiation, viruses, hyperthermia Phocomelia: a condition in which the long bones of the limbs are deficient or absent. caused by the ingestion of thalidomide by pregnant women during days 20-36 postconception Phocomelia