M7A2 Biology Essay - Lisa Smith Bio 110 M7A2 Essay 03...

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Lisa SmithBio 110M7A2 Essay03 October, 2016Dr. Leonard Simons1.Compare the embryos of chickens, humans and fish, and describe in detail how pharyngeal archesshow a shared evolutionary past?Embryonic Similarities:In a chicken, human and fish, we all share the same three stages in embryonic development. These arecalled the primary germ layers. The first is the ectoderm. The ectoderm is responsible for the outer layerof the embryo. The ectoderm also produces the surface of the skin, which is called the epidermis and italso forms the brain and nervous system. The second stage is called the endoderm. The endodermmakes the innermost layer of the developing embryo, and it develops the epithelium of the digestivetube and the organs associated with it. Lastly, the third stage involves the mesoderm. The mesodermbecomes wedged in between the ectoderm and the endoderm. It is also responsible for the productionof blood, heart, kidneys, gonads, bones, muscles, and connective tissues.All three of these steps arefound in the phyla and are responsible for the production of embryonic development of humans,chickens, and fishes. (Gilbert, 2014) (Simon, 2015, p. 161)Heinrich Rathke was the first to discover pharyngeal arches. He was able to show these structuresbecame gill supports in fish and the jaws and ears in mammals. (Gilbert, 2014)Karl Ernst Von Baer examined Panders studies of the chick embryo. He was able to prove there was acommon pattern to all vertebrate development in which each of the three germ layers gave rise to thesame organs whether it was a fish, human, or chick. Baer discovered that the notochord which is the rodof dorsal most mesoderm. This separated the embryo into right and left halves and instructed toectoderm to become the nervous system. From Baer’s divine studies of chick development andcomparison of chick embryos with other vertebrates, he was able to derive four generalizations calledBaer’s Laws. In the first law, it states that all vertebrates may start out having different patterns ofcleavage and gastrulation, they do converge at a very similar structure when they begin forming theirneural tube. After they develop, they all appear similar because they all exhibit gill arches, a notochord, aspinal cord, and primitive kidneys.During this stage the notochord which is below the neural tube isseen in every embryo. It is only later in the embryos development the features of the species start toshow. In the second Baer’s law, it states all vertebrates will have the same skin, however, only later will itstart to develop its fish scales bird feathers or claws and nails like mammals do. This stage also showedthat the limbs appeared very similar in appearance as well. Baer stated that the differences in legs, arms,and wins become will show later in development. In the third Baer’s law, it states that the embryo of agiven species, instead of passing through the adult stages of lower animals, departs more and more from

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Term
Fall
Professor
N/A
Tags
Biology, Evolution, Boundless

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