BIOL 3454 1st Edition Lecture 6I. Chapter 8 Principles of development a. Hans Spemann and Hidle Mangold i. Tissue induction using salamander embryosii. Dorsal lip from salamander gastrula, implant it on a host salamander then will get a new salamanderII. Developmental biology a. Single cell becomes a multicellular organism b. Developmental biology fell behind – fusion of genetics, evolution, functional molecular biology has closed the gap of understanding III. Historical ideasa. Preformation – the entire organism was in a miniaturized version w/in a sperm or eggb. Epigenesis – origin upon or after; an egg contains building material, activated by spermc. Hierarchy of developmental decisions – cellular # and diversity arises sequentiallyd. A cell which has committed to a fate it is determined by one of two processes i. Specification ii. Induction – usually irreversibleIV. Oocyte maturation a. Morphogenetic derminants – transcription and inducing factors, direct activation and repress genes at the correct times b. At times fertilization occurs before the oocyte has undergone meiosisc. Prophase I – GVBD – metaphase I – metaphase II – pronucleusV. Fertilizationa. Male & female gametes unite to form zygote – combo restores diploid chromosomal status b. Timing of fertilization is highly veriable among organisms with regard to oocyte maturity c. Sperm not always required for egg activationd. Contact between egg and spermi. Species specific recognition proteins ii. Prevent fertilization by another species iii. Postmating prezygotic isolating mechanism iv. Esp useful for gametes in watere. Contact and prevention of polyspermy i. -n+n=2n / n+n+n….. =Xn (not good)f. Fast block – electrical potential charge change in the egg membrane g. Slow block – cortical rxn, thousands of enzyme capsules release their contents between the egg membrane and vitellene envelopeh. Creates an osmotic water rushes in sperm washed away. Later causes the vitellene membrane to harden and physically block spermThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.VI. Sea urchin fertilizationa. Easy to find cheapb. Fertilization external easy in labc. Embryo transparent easy to see development d. Very historic, Aristotle VII. Cleavage and early development a. Blastomeres – small maneuverable cells b. No growth just a big mass dividing to a group of normally sized cells c. Polarity established (animal pole & vegetal pole)VIII. Yolk distributiona. Isolecithal – very little yolk, evenly distributedb. Mesolicithal – moderate amount of yolk at vegetal pole c. Telolecithal – lots of yolk at vegetal pole d. Centrolecithal – large centrally located yolkIX. Cleavagea. Meroblastic – lots of yolks cells sitting on top of undivided yolkb. Holoblastic – cleavage furrows extend completely though the eggX. Direct vs indirect development a. Direct development – embryo to a miniature adultb. Indirect development – multiple developmental stagesc. Either can be shortcut by matrotrophy where the mother nourishes the developing embryoXI. Development following cleavagea. Blastula – cluster of cells, usually hollow, space is the blastocoel, one layer of germ cells (one tissue layer)XII. Gastrulation & the formation of two germ layersa. Gastrulation – the conversion of the spherical blastula into a two or three layered embryob. Archenteron – the internal pouch formed in gastrulation c. Blastopore – the opening to the archenteron XIII. Developmental layers a. Three primary germ cell layers: triploblastic i. Ectoderm – most exterior becomes integument & nervous system ii. Endoderm – most of the GI tract, most of the internal organsiii. Mesoderm – most connective tissues, fluids and