Maternal and zygotic mRNAs regulate embryonic development by determining major body axes. Two of the these mRNAs code for the proteins ____ (of maternal origin) and (of zygotic origin), which are morphogens that accumulate at the end of the egg that will become the anterior end of the embryo, whereas two other mRNAs code for the morphogens ____ (maternal origin) and ____ (zygotic origin), which accumulate at the opposite end of the egg and determine the posterior end of the embryo. The dorso-ventral axis of the embryo is established by two morphogens coded for by maternal mRNAs: (1) ____, which is transcribed in the egg nucleus and accumulates in a crescent on the side of the egg that will become the dorsal surface; and (2) ____, which is transported after fertilization into blastodermal cells that will become the ventral surface, and in these cells activates the zygotic gene ____, which produces a protein that diffuses to the blatodermal cells at the opposite side of the egg and helps establish the dorso-ventral axis. There are three categories of segmentation genes: ____ genes divide the forming embryo into 3-4 large blocks or regions; ____ genes divide the large blocks into seven developmental zones; and ____ genes which subdivide the seven zones into 14 distinct bands, each of which gives rise to a particular segment with a distinct anterior and posterior end and dorsal and ventral surface.
Maternal and zygotic mRNAs regulate embryonic development by determining major body axes. Two of the these mRNAs code for the proteins ____ (of maternal origin) and (of zygotic origin), which are morphogens that accumulate at the end of the egg that will become the anterior end of the embryo, whereas two other mRNAs code for the morphogens ____ (maternal origin) and ____ (zygotic origin), which accumulate at the opposite end of the egg and determine the posterior end of the embryo. The dorso-ventral axis of the embryo is established by two morphogens coded for by maternal mRNAs: (1) ____, which is transcribed in the egg nucleus and accumulates in a crescent on the side of the egg that will become the dorsal surface; and (2) ____, which is transported after fertilization into blastodermal cells that will become the ventral surface, and in these cells activates the zygotic gene ____, which produces a protein that diffuses to the blatodermal cells at the opposite side of the egg and helps establish the dorso-ventral axis. There are three categories of segmentation genes: ____ genes divide the forming embryo into 3-4 large blocks or regions; ____ genes divide the large blocks into seven developmental zones; and ____ genes which subdivide the seven zones into 14 distinct bands, each of which gives rise to a particular segment with a distinct anterior and posterior end and dorsal and ventral surface.
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