Cleavage

Question 1

A series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller, nucleated cells.

Occurs after fertilization

Answer 1

Cleavage

Question 2

Chemical changes during cleavage

Answer 2

• DNA synthesis -> RNA synthesis -> The Midblastula Transition -> Protein Synthesis

Question 3

key proteins in Protein synthesis

Answer 3

Nuclear histones
Tubulin
Ribonucleotide reductase

Question 4

How is egg type categorized?

Answer 4

• Amount of yolk
• Distribution of Yolk
• Absence of Hard shell
• Basis on development

Question 5

Types of eggs in the basis of AMOUNT of yolk

Answer 5

• Alecithal
• Microlecithal
• Mesolecithal
• Megalecithal / macrolecithal / Polyecithal

Question 6

The yolk is almost absent

Answer 6

Alecithal

Question 7

They have very little amount of yolk. Romer and Balenski proposed the term oligolecithal.

Answer 7

Microlecithal

Question 8

They have moderate amount of yolk

Answer 8

Mesolecithal

Question 9

They have large amount of yolk.

Answer 9

Megalecithal / Macrolecithal / Polylecithal

Question 10

Types of eggs on the basis of DISTRIBUTION of yolk

Answer 10

• Isolecithal / Homolecithal
• Telolecithal
• Centrolecithal

Question 11

There is even distrubtion of the yolk in
the ooplasm.

Answer 11

Isolecithal / Homolecithal

Question 12

The yolk is found in the one pole which called as vegital pole. The yolk free pole is called as an animal pole.

Yolk unequally distributed in the
ooplasm

Answer 12

Telolecithal

Question 13

The yolk is present in the center and surrounded by ooplasm.

Answer 13

Centrolecithal

Question 14

Types of Egg cells based on the Presence or absence of Hard shell

Answer 14

• Cleidoic eggs
• Non cleidoc egg

Question 15

Such eggs are covered by hard shell for protection which is permeable for gases. Yolk present in sufficient quantity.

Answer 15

Cleidoic eggs

Question 16

They are without shell and these develop in aquatic medium and uterus of female.

Answer 16

Non cleidoc egg

Question 17

Types of Egg cells based of DEVELOPMENT

Answer 17

Determinate or Mosaic eggs

Indeterminate or Regulative Eggs

Question 18

eggs before fertilization determined the different parts of embryo

Answer 18

Mosaic eggs

Question 19

Different parts determined after third cleavage, these eggs

Answer 19

Regulative eggs

Question 20

classification of Cleavage on the Basis of YOLK

Answer 20

Total or holobastic cleavage
Meroblastic cleavage

Question 21

a type of cleavage where the entire egg undergoes division.

Answer 21

Total or Holobastic Cleavage

Question 22

types of Total or Holobastic cleavage

Answer 22

Equal holoblastic cleavage
Unequal holoblastic cleavage

Question 23

cleavage leads to the formation of blastomeres of equal size.

Answer 23

Equal holoblastic cleavage

Question 24

in mesolecithal and telolecithal eggs, cleavage leads to the formation of blastomeres of unequal size.

Among the blastomeres there are many small sized micromeres and few large sized macromeres.

Answer 24

Unequal holobastic cleavage

Question 25

Different classification of holobastic cleavage based on symmetry

Answer 25

◦ Radial holoblastic ◦ Spiral holoblastic ◦ Bilateral holoblastic ◦ Rotational holoblastic

Question 26

occurs such that the resulting daughter cells are located exactly on top of one another

Answer 26

Radial cleavage

Question 27

occurs such that the resulting daughter cells are not located exactly on top of one another; instead, they are located at a slight angle.

Answer 27

Spiral cleavage

Question 28

Has two identical halves when the blastula is cut vertically. It can be right or left. This Cleavage occurs due to unequal holoblastic

Answer 28

Bilateral Cleavage

Question 29

The first cleavage is a normal meridional division; however, in the second cleavage, one of the two blastomeres divides meridionally and the other divides equatorially - characteristics of mammals

Answer 29

Rotational cleavage

Question 30

In this type the cleavage furrows are restricted to the active cytoplasm found either in the animal pole (macrolecithal egg) or superficially surrounding the egg (centrolecithal egg).

Answer 30

Meroblastic cleavage

Question 31

Types of meroblastic cleavage

Answer 31

Discoidal Cleavage Superficial Cleavage

Question 32

cleavage furrows can be formed only in the disc-like animal pole region

Answer 32

Discoidal cleavage

Question 33

cleavage is restricted to the peripheral cytoplasm of the egg

Answer 33

Superfecial cleavage

Question 34

The developmental fate of each embryonic cell is established very early. If a cell is isolated from the 4-cell stage the embryo will not fully develop.

Answer 34

Determinate cleavage

Question 35

Early embryonic cells retain capacity to develop into a complete embryo if isolated from other cells. fates of blastomeres are not predetermined in the early embryonic period

Answer 35

Indeterminate cleavage

Question 36

an embryo that resembles mulberry, blastomeres are in early cleavage stage.

Answer 36

Morula

Question 37

a hollow ball of cells with a fluid-filled cavity, blastocoel, in the center.

Answer 37

Blastula

Question 38

forms in meroblastic cleavage yolk lies under the disc.

Answer 38

Blastodisc

Question 39

Characteristics of mammalian cleavage

Answer 39

1. Holoblastic 2. Slow and asynchronous 3. Formation of Morula and Blastocytes

Question 40

Mammalian cleavage is holoblastic, meaning the entire egg undergoes cell division

Answer 40

Holoblastic

Question 41

Mammalian cleavage is slower and more asynchronous compared to other animals, like sea urchins or frogs.

Answer 41

Slow and asynchronous

Question 42

Characteritics of mamalian cleavage: The cleavage stages lead to the formation of a morula and eventually a blastocyst, which is crucial for implantation and further development

Answer 42

Formation of Morula and Blastocytes

Question 43

differentiation of cells are not traced to differences in nuclear components of each cell but difference in cytoplasmic components

Answer 43

Intrinsic factors

Question 44

Evidence for intrinsic control

Answer 44

- Spermann's Constriction Experiment - Dentalium zygotes - Germ Plasm theory (Weismann)

Question 45

Newt zygotes were constricted using a hair loop, separating halves of the egg

Answer 45

Spemann’s Constriction Experiment

Question 46

A specific blastomere (blastomere D) consistently gives rise to mesoderm because it inherits a unique portion of vegetal cytoplasm

Answer 46

Dentalium Zygotes

Question 47

specific "germ plasm" is unequally distributed to form germ cells (PGCs), supporting the idea of intrinsic localization

Answer 47

Germ Plasm Theory

Question 48

Factors outside the cell that influence its fate

Answer 48

Extrinsic Factors

Question 49

Kinds of Experimental support for Extrinsic factors

Answer 49

- Regulative cleavage - Mosaic Cleavage - Horstandius Experiments - Morphogenic gradients

Question 50

- Seen in vertebrates and sea urchins. -If blastomeres are removed or rearranged early in development, the remaining cells can compensate and still form a complete organism

Answer 50

Regulative cleavage

Question 51

- Seen in invertebrates like Dentalium. - Removing a blastomere results in missing tissues showing early, fixed fates (intrinsic determination dominates here)

Answer 51

Mosaic cleavage

Question 52

- The egg cytoplasm contains gradients of morphogens. - These gradients provide positional information

Answer 52

Morphogenetic gradients