Two human disorders, Prader-Willi syndrome and Angelman syndrome, occur when a small deletion in a specific region of chromosome 15 is contributed by either the father or mother, respectively. Why does this small deletion not behave as a recessive allele for either syndrome, that is, why is its loss not made up for by the good copy of the region on chromosome 15 contributed by the other parent?

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#Question id: 14707

#Unit 5. Developmental Biology

Which of the following organ belongs to the internal layer of gastrula?

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#Question id: 14708

#Unit 5. Developmental Biology

Difference between gastrulation in Xenopus and sea urchin;

I. In Xenopus, formation of blastopore: mesoderm and endoderm move inside by involution over blastopore lip.

II. In sea urchin, formation of blastopore: mesodermal cells migrate into the interior; endoderm moves inside by invagination of the epithelial sheet.

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#Question id: 14709

#Unit 5. Developmental Biology

Choose right statement about cleavage pattern and gastrulation movements;

1.At the end of cleavage the animal embryo is essentially a closed sheet of cells, which is often in the form of a sphere enclosing a fluid-filled interior. Gastrulation, strictly the formation of the gut, converts this sheet into a solid three-dimensional embryonic animal body. 

2.During cleavage, cells move into the interior of the embryo, and the regions of endoderm. and mesoderm. which were originally adjacent in the cell sheet, take up their appropriate positions in the embryo.

3. Gastrulation results from a well- defined spatio-temporal pattern of change in cell shape, cell movement, and change in cell adhesiveness, the main forces of which are generated by localized contractions.

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#Question id: 14710

#Unit 5. Developmental Biology

Splitting of one cellular sheet into two more or less parallel sheets. While on a cellular basis it resembles ingression, the result is the formation of a new (additional) epithelial sheet of cells, choose right gastrulation movement;

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#Question id: 14711

#Unit 5. Developmental Biology

Choose right explanations of gastrulation movements,  

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#Question id: 14712

#Unit 5. Developmental Biology

 Match the following cleavage pattern, with their egg type and cleavage type

CLEAVAGE PATTERN	EGG TYPE	CLEAVAGE TYPE
1. HOLOBLASTIC CLEAVAGE	a. Isolecithal	I. Spiral cleavage
	b. Mesolecithal	II. Displaced radial cleavage
2. MEROBLASTIC CLEAVAGE	c. Telolecithal	III. Discoidal cleavage
	d. Centrolecithal	IV. Superficial cleavage