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Which developmental stage results in the rise of the three germ layers?
After fertilization and the formation of a zygote, the developing organism undergoes several rounds of cell division known as cleavage. During this period the cells divide but do not grow in size, resulting in a dense cell mass. The morula is formed during this portion of development.
Following cleavage, the cell develops an inner cell mass and trophoblast, or outer layer, before implantation into the uterus. At this stage, the organism is considered a blastocyst.
Soon after implantation, cells begin to differentiate into the three germ layers through a process known as gastrulation. The resulting organism is considered a gastrula.
Gastrulation is quickly followed by development of the neural crest and preliminary nervous tissue, known as neurulation. The organism is then considered a neurula.
Note that the organism can be considered an embryo at any point from the first cleavage division to approximately the eighth week of development.
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Which of the following is necessary for the development of the testes?
In order for the testes to develop, the only thing necessary is the SRY gene product, which is created from the SRY gene on the Y chromosome. DHT are involved in the development of other male sex traits during early development, such as the penis, while testosterone is involved in both early development and the development of secondary sexual traits during puberty. Wolfian excitatory hormone does not actually exist. Estrogen is not involved in the development of male sex organs.
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