1. It is possible to excise small pieces of early frog embryos, insert these pie
ID: 212498 • Letter: 1
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1. It is possible to excise small pieces of early frog embryos, insert these pieces into older embryos, and follow the course of the development of the transplanted material as the host embryo continues to develop into a tadpole. In the figure below, tissue that would later develop into an eye is removed either from the late blastula stage (a) or the much later neurula stage (b). The tissue is then transplanted into a much older host embryo, either being placed into the anterior head, the lateral head, or the central dorsum. When the donor tissue comes from a younger stage, it develops in the host into whatever tissue is appropriate for the new location, i.e. brain tissue, an ear, or a portion of the kidney. In contrast, tissue from the neurula-stage donor continues to develop into an ectopic eye regardless of its placement within the host. Explain these results. (50 points) a) Tissue from late blastula b) Tissue from neurula or early gastrula Area that will later become neural tissue Excise tissue that would later become an eye Excise tissue that would later become an eye Transplant into older host embryo Transplant into older host embryo Develops into an eye nto a kidney Develops into head material Develops into an ear Develops into an eye Develops into an eye (eye, brain)Explanation / Answer
When tissue (which later ould have formed eye) was collected from the blastula stage and transplanted into an older embryo, either in the anterior or lateral head or central dorsum it formed whatever tissue was appropriate for the location. This happened because the fate of the cells collected from the young blastula stage wasn't sealed. Hence when transplanted into the older embryo, the surrounding secretion of molecules changed the fate of the cells resulting in brain tissue or ear or kidney.
However, when tissue collected from neurula stage was collected and transplanted, their fate was already determined. Hence, even after transplantation, they resulted into eye, regardless of their position.
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