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Dev Bio > C5: Cleavage > Flashcards

C5: Cleavage Flashcards

1
Q

in embryology, it is the first few cellular divisions of a zygote (fertilized egg)

A

Cleavage

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2
Q

describe the first three dvison of a zygote.

A

initially, the zygote splits along a longitudinal plane;
the second division is also longitudinal, but at 90 degrees to the plane of the first; third division is perpendicular to the first two and is equatorial in position

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3
Q

these early divisions produce separate cells called __

A

blastomeres

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4
Q

the rapid, multiple rounds of cell division are termed __

A

cleavage

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5
Q

after the cleavage has produced over 100 cells, the embryo is called a ___

A

blastula

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6
Q

the __ is usually a spherical layer of cells (___) surrounding a fluid-filled or yolk-filled cavity (the ___)

A

blastula;
(blastoderm);
blastocoel

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7
Q

mammals at this stage (cleavage has produced over 100 cells) form a structure called the ___, characterized by an ___ that is distinct from the surrounding blastula

A

blastocyst;
inner cell mass

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8
Q

each cell within the blastula is called a __

A

blastomere

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9
Q

when the embryo consists of approximately 16 cells, it is called a ___ (from the Latin word meaning “___”)

A

morula;
mulberry

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10
Q

starting after the eight-cell stage, the embryos of placental mammals enter into a phase called ___

A

compaction

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11
Q

compaction is mediated by concentration of calcium (Ca++)-activated cell adhesion molecules (such as ___), in a ring around the __ surface of the ___

A

E-cadherin;
apical;
blastomeres

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12
Q

through the activity of a ____, Na+ and water (H2O) move across the epitheliumlike outer blastomeres and accumulate in spaces among the inner blastomeres

A

sodium (Na+), potassium (K+)–adenosine triphosphatase (ATPase)–based Na+ transport system

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13
Q

the process wherein Na+ and water (H2O) move across the epitheliumlike outer blastomeres and accumulate in spaces among the inner blastomeres is called ___

A

cavitation

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14
Q

the cavitation process takes about __ days after fertilization

A

4

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15
Q

the fluid-filled space is known as ___

A

blastocoele (blastocyst cavity)

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16
Q

once cavitation occurs, and a blastocoeleis formed, the embryo as a whole is known as a ___

A

blastocyst

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17
Q

the ___ stage, the embryo, which is still surrounded by the zona pellucida, consists of two types of cells (__ and __)

A

blastocyst;
Trophoblast and Inner cell mass

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18
Q

outer epithelial layer

A

Trophoblast

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19
Q

small inner group of cells

A

Inner cell mass

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20
Q

each blastomere at the ___ and the ___ stage contributes cells to both the inner cell mass and the trophoblast

A

two-cell; four-cell

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21
Q

the end of the blastocyst that contains the inner cell mass is known as the ___, and the opposite end is called the ___

A

embryonic pole;
abembryonic pole

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22
Q

cells of the __ give rise to the body of the embryo itself in addition to several extraembryonic structures, whereas cells of the ___ form only extraembryonic structures, including the outer layers of the ___

A

inner cell mass;
trophoblast;
placenta

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23
Q

there is increasing evidence that ____ acts to maintain mitotic activity in the overlying trophoblast

A

fibroblast growth factor-4

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24
Q

(a growth factor secreted by cells of the inner cell mass),

A

fibroblast growth factor-4

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25
Q

The first cleavage of frog’s egg was observed by ____ in 1738.

A

Jan Swammerdam

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26
Q

The entire process of cleavage in frog’s egg was studied by ___ and _____ in 1824

A

Pierre Prevost; Jean Baptiste André Dumas

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27
Q

planes of cleavage are named depending on the position of the ___

A

cleavage furrow

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28
Q

The Planes of Cleavage (4)

A

1.) Meridional plane
2.) Vertical plane
3.) Equatorial plane
4.) Latitudinal plane

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29
Q

– the plane of the cleavage lies on the animal vegetal axis; it bisects both the poles of the egg; the egg is divided into two equal halves

A

Meridional plane

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30
Q

the cleavage furrows may lie on either side of the meridional plane; the furrows pass from animal to vegetal pole; the cleaved cells may be unequal in size

A

Vertical plane

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31
Q

this cleavage plane bisects the egg at right angles to the main axis; lies on the equatorial plane; divides the egg into two halves

A

Equatorial plane

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32
Q

similar to the equatorial plane, but it lies on either side of the equator; also called as transverse or horizontal cleavage

A

Latitudinal plane

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33
Q

yolk-rich pole

A

Vegetal Pole

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34
Q

yolk-poor pole

A

Animal Pole

35
Q

___is generally displaced towards the animal pole

A

zygotic nucleus

36
Q

the ___ of the yolk and its ___ affect the process of cleavage

A

amount; distribution

37
Q

types of eggs based on yolk characteristics (4)

A
  1. Isolecithal
  2. Mesolecithal
  3. Telolecithal
  4. Centrolecithal
38
Q

type of eggs that sparse evenly distributed yolk; e.g. ___ and ___

A

Isolecithal;
sea urchin and mouse

39
Q

type of egg that has moderate amount of yolk and often unevenly distributed; e.g. __

A

Mesolecithal;
frog

40
Q

type of egg that has dense yolk concentrated at one end; e.g. ___ and __

A

Telolecithal;
bird and reptile

41
Q

type of egg that has yolk concentrated at the middle of the egg; e.g. ___

A

Centrolecithal;
fly

42
Q

Main Cleavage Patterns (2)

A
  1. Total or holoblastic cleavage
  2. Meroblastic cleavage
43
Q

the cleavage furrow bisects the entire egg; such a cleavage may be either equal or unequal

A

Total or holoblastic cleavage

44
Q

2 types of holoblastic cleavage

A

a. Equal holoblastic cleavage
b. Unequal holoblastic cleavage

45
Q

cleavage leads to the formation of blastomeres of equal size such that in ____ and ___ eggs,; e.g. __ and ___ mammals

A

Equal holoblastic cleavage;
microlecithal and isolecithal
amphioxus and placental

46
Q

cleavage leads to the formation of blastomeres of unequal size such as in ___ and ___ eggs; among the blastomeres there are many small sized micromeres and a few large sized macromeres

A

Unequal holoblastic cleavage;
mesolecithal and telolecithal

47
Q

the cleavage furrows are restricted to the active cytoplasm found either in the animal pole (__ egg) or superficially surrounding the egg (___ egg)

A

meroblastic cleavage
macrolecithal;
centrolecithal

48
Q

the cytoplasm is restricted to the narrow region in the animal pole; hence cleavage furrows can be formed only in 3 the disc-like animal pole region; such a cleavage is called ___; e.g. __ and ___

A

discoidal meroblastic cleavage;
birds and reptiles

49
Q

___ - in ___ eggs, the cleavage is restricted to the peripheral cytoplasm of the egg; e.g. __

A

Superficial cleavage;
centrolecithal;
insects

50
Q

Laws of Cleavage (2)

A

. Sachs’ Laws;
Balfour’s Law

51
Q

this law was proposed by ___ in 1877 which states that “cells tend to divide into equal daughter cells” and “each new division plane tends to intersect the preceding plane at right angles” (acts to maintain the spheroidal shape of blastomeres)

A

. Sachs’ Laws (Julius von Sachs)

52
Q

this lawwas proposed by ___ in 1885 ▪ states that “the speed or rate of cleavage in any region of egg is __ proportional to the amount of yolk it contains”

A

Balfour’s law (Francis Maitland Balfour);
inversely

53
Q

cleavage patterns based largely on the orientation of the division planes (2)

A

radial cleavage;
spiral cleavage

54
Q

simplest pattern; in which successful division planes are at 90 degree angles relative to each other; this results in the blastomeres aligned directly over or to the side of one another

A

radial cleavage

55
Q

the division planes are not at 90-degree angles, resulting in blastomeres that are not aligned directly over or beside one another

A

spiral cleavage

56
Q

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

characteristic of ___
results in ___ cells

A

Radial Cleavage;
deuterostomes;
indeterminant

57
Q

the cells divide such that each cell in the top four cell plane is directly over one other cell in the bottom plane

A

Radial Cleavage

58
Q

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

characteristic of __
results in ___ cells

A

Spiral Cleavage
protostomes;
determinant

59
Q

the cells divide at slight angles to one another, so that the none of the four cells in one plane of the eight-cell stage is directly over a cell in the other plane

A

Spiral Cleavage

60
Q

Classification of Cleavages based on the Potentiality of the Blastomeres for the Future Development (2)

A

a. Determinate
b. Indeterminate

61
Q

the developmental fate of each embryonic cell is established very early; fate of each blastomere is predetermined in the early embryonic stage itself

A

a. Determinate

62
Q

in determinate cells, if a cell is isolated from the __ stage the embryo will not fully develop

A

4-cell

63
Q

examples of determinate (3)

A

annelids, mollusks and ascidians (which produce mosaic type of eggs)

64
Q

early embryonic cells retain capacity to develop into a complete embryo if isolated from other cells; cleavage produces blastomeres which are qualitatively ___ or ___

A

b. Indeterminate;
equipotential or totipotent

65
Q

when they are isolated, they develop into complete embryos ▪ this is because the fates of blastomeres are not predetermined in the early embryonic period

A

b. Indeterminate cells

66
Q

examples of indeterminate organisms (2)

A

vertebrates and certain invertebrates such as echinoderms (which produce regulative type of eggs)

67
Q

this type of cleavage occurs in centrolecithal eggs

A

Superficial Cleavage

68
Q

the early divisions occur in the surface layer of the egg and cleavage furrows do not extend into the central yolk

A

Superficial Cleavage

69
Q

in this cleavage, the zygote nucleus lies in the center of the egg ▪ it divides repeatedly without the division of the egg cytoplasm

A

Superficial Cleavage

70
Q

from the early cell lineage studies and the recognition of mosaic development of mainly invertebrate embryos, the concept of ____ was developed

A

cytoplasmic localization

71
Q

an invariant cleavage pattern divides the embryo into different cell lines that differentiate according to the information they obtain from differentially distributed cytoplasmic factors

A

cytoplasmic localization

72
Q

In cytoplasmic localization, the organization of the cytoplasm of the egg before and after fertilization is established by the redistribution of ___

A

ooplasmic determinants

73
Q

examples of such ‘mosaic’ development have been well studied in __ (5)

A

ascidians, sea urchins, spiralians, Caenorhabditis elegans and also in the vertebrate embryo of Xenopus

74
Q

after __ cleavage, the rest of the cleavages are ___ and completely delimited cells are formed all over the germinal disc which is termed as __;

this outcome of cleavage called ____ helps seal the developmental fate of each cell’s descendants.

A

third;
irregular;
blastoderm;
cytoplasmic localization

75
Q

___ acts as a trigger to initiate a program of events starting with cleavage, and continuing with gastrulation and neurulation, etc.

A

fertilization

76
Q

although fertilization results in union of maternal and paternal genomes, ___ activity is not required until the __ stage

A

zygotic gene;
blastula

77
Q

after fertilization and through cleavage, the maternal, paternal and zygotic genomes are completely dispensible
▪ this is because in the egg, there exists a stockpile of _____ which govern __ through cleavage to the blastula stage

A

maternally derived mRNAs;
embryogenesis

78
Q

following the formation of the blastula, ___ is activated, which carries the embryo through the rest of ___

A

zygotic gene transcription;
embryogenesis

79
Q

Evidence for maternal mRNA control of early development (4)

A
  1. maternal trait dominance in interspecific hybrids
  2. cleavage in enucleate embryos
  3. transcriptional inhibition does not prevent cleavage
  4. translational inhibition prevents cleavage
80
Q

____ encode gene products (RNA or protein) that are required in early development prior to zygotic transcription

A

maternal effect genes

81
Q

using the rudimentary gene of Drosophila as an example, by definition, whenever, mothers are ____, their progeny are ___ despite being genotypically viable

A

homozygous mutant;
embryonic lethal

82
Q

After fertilization, one of the first roles of maternal factors is the processing of the ___, which is necessary for its participation in embryogenesis;

second role is the removal of ____ (RNA and protein), ;

and a third is the robust activation of the ____, which is essential for the development of the embryo beyond two cells

A

male genome;
maternal detritus;
embryonic genome

83
Q

targeted ___ experiments in mice have provided researchers with a wealth of insight into candidate maternal factors that participate in the regulation of these essential early steps of development

A

mutagenesis

84
Q

“mother’s genotype determines offspring’s phenotype”

A

maternal effect rule

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