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Edit5 X1. Gases are exchanged in a mammalian embryo in theamnion. B) hypoblast. C) chorion. D) trophoblast. E) yolk sac.2. Changes in both cell shape and cell position occur extensively duringA) gastrulation, but not organogenesis or cleavage. B) organogenesis, but notgastrulation or cleavage. C) cleavage, but not gastrulation or organogenesis.D) gastrulation and organogenesis but not cleavage. E) gastrulation,organogenesis, and cleavage.3. Changes in both cell shape and cell position occur extensively duringA) gastrulation, but not organogenesis or cleavage. B) organogenesis, but notgastrulation or cleavage. C) cleavage, but not gastrulation or organogenesis.D) gastrulation and organogenesis but not cleavage. E) gastrulation,organogenesis, and cleavage.Inhumane identical twins are possible because A) of the heterogeneous |
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Answer» Answer:t is not surprising that mammalian cleavage has been the most difficult to study. Mammalian eggs are among the smallest in the animal kingdom, making them hard to manipulate experimentally. The HUMAN ZYGOTE, for instance, is only 100 μm in diameter—barely visible to the eye and less than one-thousandth the volume of a Xenopus egg. Also, mammalian zygotes are not produced in numbers comparable to sea urchin or frog zygotes, so it is difficult to obtain enough material for biochemical studies. Usually, fewer than TEN eggs are ovulated by a female at a given time. As a FINAL hurdle, the development of mammalian embryos is accomplished within another organism, rather than in the external environment. Only recently has it been possible to duplicate some of these INTERNAL conditions and observe development in vitro. Explanation: |
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