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Lecture 12

BIOSC 0160 Lecture 12: Biology 2 Lecture 2.2: Animal Developmental Processes

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Biological Sciences
BIOSC 0160

Biology Week 8 Lecture 2.2 Segmentation genes: subdivide embryo into smaller areas, demarcating the embryo segments and eventually specifying the identityrole of each segment o Bicoid and other maternal effect genes are at the top of a regulatory gene of hierarchy of these Hox genes occur in two clusters on chromosome 3 o Order on chromosome is the same order of position expressed in embryo o Highly conserved in animals where they specify position of structures Homeotic mutations: altered Hox genes that result in drastic transformations to the body plan Morphogens: maternally expressed gene products Evodevo: field of biology which studies how changes in the expression of developmentally important genes can lead phenotypic diversity and the formation of new species o Highly conserved tool kit genes like Hox genes (direct pattern formation) o Genetic switches (DNA regulatory regions, transcription factors, signaling transduction molecules) regulate tool kits determine where, when, and how they are expressed in development o Modularity: independence of developmental processes (module changes without changing the whole organism) results from multiple switches o Heterometry: amount of expression o Heterochrony: time of expression o Heterotropy: location of expression Fertilization: initial developmental event in sexual reproduction o Union of male and female gametes o Restores diploid number o Sperm entry establishes polarity in the zygote o Polyspermy: fertilization of the egg by more than one sperm Increases number of centrile and chromosome number Fast block: begins shortly after egg contact with fertilization sperm and lasts about 60sec. Plasma membrane is depolarized when NA+ channels are opened and Na+ enters the cell, which prevents additional sperm from entering (dont know why this works) Slow block: cortical reaction and fertilization membraneenvelope formation Ca2+ are released from intracellular stores triggering the formation of the fertilization membrane which removes excess sperm Ca2+ release triggers cortical reaction o Enzymerich cortical granules fuse with the cell membrane, release their contents outside the plasma membrane vis exocytosis (between cell membrane and vitelline layer) o Enzymes digest sperm receptors, water rushes into the space because of the release of solutes, and the fertilization envelope is pushed away from the egg removing the sperm o Species recognition: external fertilization
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