Bio study guide IVReading 18.4, 18.5, 21.61) Be able to explain how the concentration of cytoplasmic determinants leads to differences in celldetermination in early development.a. Cytoplasmic determinants are the maternal substances in the egg that influence thecourse of early development.i. MRNA/proteins/other substances are distributed unevenly in the unfertilizedegg, and this unevenness definitely has an impact on the development of thefuture embryo.b. Another thing that affects development is the environment around a cell, becomingreally important as the number of embryonic cells increases.c. Cell determination gives a cell its “fate” for when it develops later on.i. So, they lead to differences in cell determination in early development becauseevery cell is going to be different for when its “fate” is determinedd. Cell differentiation is the process by which cells become specialized in structure andfunctioni. Induction is when signals from nearby embryonic cells cause changes in thetarget cells; these signals affect development because they send a cell down acertain developmental path by causing changes in its gene expression thateventually result in observable cellular changes.1. Thus, these interactions btwn embryonic cells help induce differentiationof the many specialized cell types making up a new organisme. **DETERMINATION COMES BEFORE DIFFERENTIATION; ONCE A CELL UNDERGOESDIFFERENTIATION, IT IS PERMANENTLY ON THAT PATH TO BECOME THAT CERTAIN CELLTYPE**2) Know that genes controlling development are expressed in a specific sequencea. The outcome of determination, observable cell differentiation, is marked by theexpression of genes for tissue‐specific proteins.i. These proteins are only found in a specific cell type and give the cell itscharacteristic structure and functionii. On the molecular level, different sets of genes are sequentially expressed in aregulated manner as new cells arise from division of their precursors.1. Several steps in gene expression can be regulated, especiallytranscription (remaining as the principal regulatory point for maintainingappropriate gene expression)2. The master regulatory gene in muscle cells is a major factor thatcontributes to the process of transcription to express MyoD andtherefore create skeletal muscle cells3) Know that the earliest genes expressed determine axis polarity, followed by organization intobody regions, segmentation, and specific characteristics (Drosophila).a. Pattern formation: a spatial organization in which the tissues and organs of an organismare all in their characteristic places (cytoplasmic determinants and inductive signals bothcontribute to this)b. Certain molecular cues that control pattern formation (called positional information) areprovided by cytoplasmic determinants and inductive signals; these cues tell a cell itslocation relative to the body axes and to neighboring cells and determine how the celland its offspring will respond to future molecular signals.4) Know that developmental genes are highly conserved across animals (be able to explain what‘highly conserved’ means)a. Researchers discovered very similar nucleotide sequences (aka homeobox) btwndrosophila flies and other organisms, especially humans.b. Hox genes are highly conserved across animals (humans have the same genes as fruitflies)i. The order on the body in which Hox genes are expressed is the same as theorder on the chromosome.c. Highly
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