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BIOL 103 (103)
Chapter 17


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BIOL 103
Virginia K Walker

BOAG CHAPTER 17 (pg 414-422) DEVELOPMENT IN ANIMALS 1. oocyte is critical to establishing pattern of development that will produce an adult organism -has anterior + posterior ends 2. Blastoderm; developed from a zygote -lots of nuclei scattered throughout yolk; eventually they migrate/line up along cell membrane 3. Gastrulation: involves well-ordered rearrangement of cells in the embryo -produces a gastrula: made of the layers ectoderm (outside), mesoderm (in between), and endoderm (inside) 4. Embryo divided into segmented body pattern -head, thorax, abdomen 5. Larva: free-living organism that is morphologically very different from the adult 6. Pupa: through metamorphosis, changes into a mature adult PHASE 1: MATERNAL EFFECT GENES PROMOTE FORMATION OF MAIN BODY AXES -maternal effect genes controls where morphogen concentrations are -morphogen activates certain genes in certain regions of the embryo, depending on if it's in high [ ] -morphogen activates genes in certain regions but not others; role in pattern formation + segregation -segmentation genes: genes required for embryo to develop a segmented pattern -->gap gene: mutation results in adjacent segments missing in larva -->pair-rule gene: mutation causes alternating segments or parts of segments to be deleted -->segment-polarity gene: mutations cause portions of segments to be missing either an anterior or posterior region; adjacent regions become mirror images of each other PHASE 2: SEGMENTATION GENES DIVIDE EMBRYO INTON SEGMENTS -maternal effect genes promote phase 1 pattern development -gap genes + m.e. genes activate pair-rule genes -then segment-polarity genes are activated--> expression of gene now corresponds to segments of adult PHASE 3: HOMEOTIC GENES CONTROL DEVELOPMENT OF SEGMENT CHARACTERISTICS -cell fate: ultimate morphological features that a cell/group of cells will adopt -each segment begins to develop own unique characteristics -homeotic: changes in cell/tissue identity in which one body part is replaced by another --> caused by mutant alleles of homeotic genes --> eg. legs where antennae should be --> homeotic genes contain a homeobox sequence (found in genes affecting pattern development), which encodes a region of the protein called a homeodomain: f'ns in binding to the DNA PHASE 4: STEM CELLS CAN DIVIDE + DIFFERENTIATE INTO SPECIALIZED CELL TYPES -so far, patterns of gene expression occur during development; these genes control basic body plan of organism -morphological difference b/w 2 differentiated cells is due to gene regulation: same genes, different expression that underlies cell differentiation Stem cells: divides + supplies the cells that construct the bodies of all organisms --> capacity to divide + their daughter cells can differentiate into 1+ specialized cell types -->one daughter can remain undiff., while the ot
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