Distinguish between a blastula, a blastomere, a blastopore, and a blastocoel. What happens at the mid-blastula transition in Xenopus? Which pan of the Xenopus blastula becomes the mesoderm? Where does the dorsal lip tissue end up when Xenopus gastrulation is finished? Where does the vegetal pole end up when gastrulation is finished? How is the central nervous system formed? Where does die neural crest come from and What does it become? Solution Answer: 1. The blastula is the whole embryo after the sperm enters and the egg cleaves a bunch of times. It is a ball of cells with a fluid filled cavity called the blastocoel. It contains a hole in the center containing vitellus in it. A blastomere is a type of cell produced by cleavage (cell division) of the zygote after fertilization and is an essential part of blastula formation. The blastopore is the hole forms during gastrulation as cells move from the vegetal pole toward the other side and connects to the ectoderm. The blastopore only refers to the opening at the bottom of the cell. The actual cavity being formed as the cells move within the blastocoel is called the achenteron. 2. Midblastula transition is a stage in the blastula stage of embryonic development in Xenopus during which zygotic gene transcription is activated. 3. The hollow ball, blastula attains a cup like structure with an inner layer of endoderm and an outer layer of ectoderm. This cup-like structure is called a gastrula. The mesoderm is formed when cells begin to form a middle layer between the endoderm and ectoderm. 4. Early on, the dorsal lip of the blastopore forms due to the contraction of bottle cells. The blastopore continues to develop from the early frown until it can be observed as a complete circular ring of involuting cells. Convergent extension closes the blastopore at the yolk plug and elongates the embryo along the anterior--posterior axis.

1. Distinguish between a blastula, a blastomere, a blastopore, and a blastocoel. What happens at
the mid-blastula transition in Xenopus? Which pan of the Xenopus blastula becomes the
mesoderm? Where does the dorsal lip tissue end up when Xenopus gastrulation is finished?
Where does the vegetal pole end up when gastrulation is finished? How is the central nervous
system formed? Where does die neural crest come from and What does it become?
Solution
Answer:
1. The blastula is the whole embryo after the sperm enters and the egg cleaves a bunch of times.
It is a ball of cells with a fluid filled cavity called the blastocoel. It contains a hole in the center
containing vitellus in it.
A blastomere is a type of cell produced by cleavage (cell division) of the zygote after fertilization
and is an essential part of blastula formation.
The blastopore is the hole forms during gastrulation as cells move from the vegetal pole toward
the other side and connects to the ectoderm. The blastopore only refers to the opening at the
bottom of the cell. The actual cavity being formed as the cells move within the blastocoel is
called the achenteron.
2. Midblastula transition is a stage in the blastula stage of embryonic development in Xenopus
during which zygotic gene transcription is activated.
3. The hollow ball, blastula attains a cup like structure with an inner layer of endoderm and an
outer layer of ectoderm. This cup-like structure is called a gastrula. The mesoderm is formed
when cells begin to form a middle layer between the endoderm and ectoderm.
4. Early on, the dorsal lip of the blastopore forms due to the contraction of bottle cells. The
blastopore continues to develop from the early frown until it can be observed as a complete
circular ring of involuting cells. Convergent extension closes the blastopore at the yolk plug and
elongates the embryo along the anterior--posterior axis