Bio; Lecture 14; Animal Evolution

Bio; Lecture 14; Animal Evolution - Principles of Biology 2...

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Principles of Biology 2 BIO U103 2/12/07 Animal Evolution Fate of a cell is determined by: o Presence of cytoplasmic determinants o Connection and contact with neighboring cells o Amount and distribution of yolk o Genes: homeobox genes—regulate development o Inactivation of DNA Cleavage is determined by: o Amount of yolk Holoblastic (cleaves right through) Mroblastic (unable to cleave right through cells initially) o Genes controlling the symmetry of cleavage Radial, spiral, and rotational. Sea Urchins o Radial holoblastic cleavage o Blastomeres sit exactly on op of each other o Egg is isolecithal o Cleavage is holoblastic and radial o Cleavage produces a blastula : a hollow ball of 128 cells. Blastocoel : cavity within the blastula—filled with fluid Blastocist —fluid that fills the blastocoel. o Gastrulation: Begins at vegetable pole Area of cells start to push in, and form a dent Invagination : process of cells pushing into the blastocoel. Archentern : formed by invagination— primitive gut —envelope of tissue formed inside the blastocoel via gastrulation Involution: when the archenteron takes over the blastocoel. Cells at the top start moving down toward the dent/hole (blastopore) Blastopore: hole at which gastrulation occurs Ectoderm: outer layer of cells Endoderm: inner layer of cells (primitive gut) Mesoderm: during invagination, some cells migrate along with endoderm inside the blastocoel—this tissue makes up the mesoderm located between ectoderm and endoderm the endoderm continues its involution until it reaches ectoderm at another side of the embryo Frog Embryology o Embryo is telolecithal .—there is a lot of yolk o Because of this, the blastocoel during the blastula stage is much smaller o The blastocoel is located at the animal pole - 1 -
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Bio; Lecture 14; Animal Evolution - Principles of Biology 2...

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