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time to develop, but the maximum time spent in utero is limited by other factors, such as relative size of the final fetus to the mother (ability of the fetus to pass mother's genital tract to be born), limited resources for the mother to nourish herself and her fetus, etc. Thus, to develop such a complex and advanced brain in the end, the mammalian embryo needed to start this process earlier and to perform it faster.
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tends to begin at earlier stages of embryonic development and to yield more structurally advanced brain at each stage, in comparison with lower chordates. The evolutionary reason for such a change likely was that the advanced and structurally complex brain, characteristic of mammals, requires more
156:; during the earliest stages of development, the embryo is largely indistinguishable from another mammal. However, there are phenomena found in human beings not found in all other mammals, as well as phenomena occurring in other mammals, but not in humans.
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in the embryo is relatively small in size, in comparison with both the size of the embryo itself and the size of yolk sac in embryos of comparable developmental age from lower
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Another difference is that during the development of embryonic genitourinary tract, in case of female embryo of placental and marsupial mammals, the
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There are also several other differences from embryogenesis in lower chordates. One such difference is that in mammalian embryos development of the
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84:. The fact that an embryo in both placental mammals and marsupials undergoes the process of implantation, and forms the
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Findlay JK, Gear ML, Illingworth PJ, Junk SM, Kay G, Mackerras AH, Pope A, Rothenfluh HS, Wilton L (April 2007).
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compared to humans: each unborn animal is surrounded by placental tissue and is lodged along one of two long
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The difference between a mammalian embryo and an embryo of a lower chordate animal is evident starting from
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nor lower chordates have. In every case, including monotremata embryos, the milk glands also develop.
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stage. Due to that fact, the developing mammalian embryo at this stage is called a
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rather than in the center of the pear-shaped uterus found in a human female.
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406:"A sequence of events in the uterus prior to implantation in the mouse"
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The anatomy of the area surrounding an embryo or fetus is different in
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268:"Development: Cell fate decisions in mammalian embryogenesis"
301:"Growth factor superfamilies and mammalian embryogenesis"
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in these species does not contain significant amounts of
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42:Difference from embryogenesis of lower chordates
111:, not a blastula, which is more generic term.
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410:Journal of Assisted Reproduction and Genetics
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365:"Human embryo: a biological definition"
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130:is formed, a structure that neither
31:which leads to the development of a
299:Mercola M, Stiles CD (March 1988).
138:Difference from human embryogenesis
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345:. Georgia Institute of Technology
343:Developmental Biology Interactive
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249:"Early Mammalian Development"
164:Mammals do not have the same
800:Animal developmental biology
456:Photo of blastocyst in utero
168:released from their embryo.
166:human chorionic gonadotropin
768:Splanchnopleuric mesenchyme
713:Splanchnopleuric mesenchyme
492:Human embryonic development
404:Yoshinaga K (August 2013).
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422:10.1007/s10815-013-0093-z
199:Mammalian Parthenogenesis
60:nourish their developing
773:Somatopleuric mesenchyme
685:Somatopleuric mesenchyme
494:in the first three weeks
204:Drosophila embryogenesis
25:cellular differentiation
339:"Mammalian Development"
272:Nature Reviews Genetics
17:Mammalian embryogenesis
657:Regional specification
178:litter-bearing animals
116:central nervous system
763:Intraembryonic coelom
382:10.1093/humrep/del467
317:10.1242/dev.102.3.451
266:Koch L (2014-12-18).
253:Developmental Biology
214:Developmental biology
152:develop similarly to
52:Due to the fact that
29:prenatal development
247:Gilbert SF (2000).
209:Plant embryogenesis
144:Human embryogenesis
118:and especially the
369:Human Reproduction
19:is the process of
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512:Oocyte activation
172:Non-human mammals
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675:Surface ectoderm
638:Primitive groove
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416:(8): 1017–22.
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98:umbilical cord
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27:during early
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21:cell division
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753:Intermediate
695:Neural crest
650:Gastrulation
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347:. Retrieved
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56:mammals and
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690:Neurulation
615:Archenteron
607:Germ layers
557:Trophoblast
305:Development
132:monotremata
746:Somitomere
633:Blastopore
597:Trilaminar
547:Blastocyst
542:Blastocoel
537:Cavitation
527:Blastomere
349:2019-03-15
235:References
219:Blastomere
109:blastocyst
76:, and the
58:marsupials
579:Hypoblast
570:Bilaminar
88:with its
82:chordates
54:placental
33:mammalian
794:Category
736:Paraxial
723:Mesoderm
705:Endoderm
667:Ectoderm
645:Gastrula
584:Epiblast
522:Cleavage
440:24052329
391:17178746
188:See also
105:blastula
94:placenta
78:yolk sac
66:placenta
64:via the
593:Week 3
566:Week 2
431:3790116
325:3053123
150:mammals
86:chorion
62:embryos
741:Somite
532:Morula
517:Zygote
500:Week 1
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224:Morula
160:Humans
154:humans
128:uterus
68:, the
36:embryo
278:: 5.
148:Most
120:brain
436:PMID
387:PMID
321:PMID
229:Cdx2
96:and
74:yolk
70:ovum
23:and
426:PMC
418:doi
377:doi
313:doi
309:102
280:doi
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