Animal Cleavage patterns- L12

Question 1

What is cleavage?

Answer 1

A series of rapid cell divisions after fertilisation WITHOUT GROWTH, that divides the embryo into a number of small cells.

Question 2

Vegetal pole is..

Answer 2

yolky

Question 3

Animal pole is…

Answer 3

non-yolky

Question 4

Before fertilisation the egg is what?

Answer 4

radially symmetrical

Question 5

After fertilisation the cytoplasm..

Answer 5

streams towards vegetal pole and back towards animal pole but is displaced to one side.
CREATES BILATERAL SYMMETRY- establishes left and right side of embryo.

Question 6

The corticol cytoplasam rotates..

Answer 6

relative to inner cytoplasam

Question 7

The gray crescent is created by…

Answer 7

rotation

Question 8

Which is pigmented the animal corticol or the vegetal corticol?

Answer 8

Animal .

Question 9

Conklin (1902)

Yellow cytoplasm and the determination of cell fate

Answer 9

-Yellow cytoplasm in some cells after cleavage in tunicate
- Only these cells form muscle tissues
SUPPORTED WEISMANNS CONCEPT OF CYTOPLASMIC DETERMINANTS.

Question 10

The yellow cytoplasm contains mRNA for a transcription factor called what?

Answer 10

Macho1, associated with switching on genes associated with muscle cell development.

Question 11

What are the three types of cleavage?

Answer 11

Radial- Deuterostomes
Spiral- Protostomes
Superficial- insects

Question 12

What cleavage do embryos show?

Answer 12

ROTATION HOLOBLASTIC CLEAVAGE

Cleavage is unequal at z-cell stage: AB cell is larger.

Question 13

Cytoplasmic movement- supports mosaic development. Why?

Answer 13

P granules in the cytoplasm become contracted in posterior after fertilisation. By 26 cell stage they are only in p4 cells which give rise to germ cells.