Lecture 7 - Cleavage Flashcards
1
Q
characteristics of cleavage
A
- rapid mitotic division transforming unicellular to multicellular embryo
- no growth in size
2
Q
what happens to ratio of nucleus to cytoplasm
A
progressively increases
3
Q
what are the phases that are not included during cleavage
A
G1 or G2 phase, no cell growth
4
Q
what increases during cleavage
A
nuclear material at expense of cytoplasm
5
Q
where is the nuclear material from
A
- ribonucleic acids in cytoplasm
- low molecular weight precursors
6
Q
what synthesis is limited during cleavage
A
rRNA and tRNA synthesis
7
Q
when does rRNA synthesis resume
A
gastrulation
8
Q
most important for cleavage
A
- nuclear histones
- tubulin
- ribonucleotide reductase
9
Q
types of eggs based on amount of yolk
A
- macrolecithal
- mesolecithal
- microlecithal
10
Q
has large amount of yolk
A
macrolecithal
11
Q
has moderate amount of yolk
A
mesolecithal
12
Q
has small amount of yolk
A
microlecithal
13
Q
types of eggs based on the distribution of yolk
A
- telolecithal
- isolecithal
- centrolecithal
14
Q
concentrated in one region of the egg
A
telolecithal
15
Q
evenly distributed throughout the egg
A
isolecithal
16
Q
concentrated in the center of the egg
A
centrolecithal
17
Q
patterns of cleavage
A
- incomplete/meroblastic
- complete/holoblastic
18
Q
types of cleavage under isolecithal egg
A
- radial cleavage
- spiral cleavage
- bilateral cleavage
- rotational cleavage
19
Q
animals with complete radial cleavage
A
- echinoderms
- amphioxus
20
Q
animals with complete spiral cleavage
A
- annelids
- molluscs
- flatworms
21
Q
animals with complete bilateral cleavage
A
tunicates
22
Q
animals with complete roational cleavage
A
- mammals
- nematodes
23
Q
types of cleavage under mesolecithal egg
A
displaced radial cleavage
24
Q
animals with displaced radial cleavage
A
amphibians
25
types of cleavage under telolecithal egg
1. bilateral cleavage
2. discoidal cleavage
26
animals with incomplete bilateral cleavage
cephalopod molluscs
27
animals with discoidal cleavage
- fish
- reptiles
- birds
28
types of cleavage under centrolecithal egg
superficial cleavage
29
animals with superficial cleavage
most insects
30
the entire egg is not completely divided
meroblastic cleavage
31
- under meroblastic cleavage
- division of the egg is confined to a disc of cytoplasm
- occurs in strongly telolecital eggs like frog, reptiles, and birds
discoidal cleavage
32
complete division of the egg occurs
holoblastic cleavage
33
- under holoblastic cleavage
- division of the egg is complete but cells are unequal in size
displaced radial cleavage
34
- under holoblastic cleavage
- with no obvious polarity
rotational cleavage
35
blastomeres lie directly on top of each other
radial cleavage
36
blastomeres lie on the junction between lower blastomeres due to oblique position of spindle
spiral
37
two types of turn in spiral cleavage
1. dextral cleavage
2. sinistral cleavage
38
dextral cleavage
turn spiral in clockwise
39
sinistral cleavage
turn spiral in counterclockwise
40
division in centrolecithal egg
only nuclear division, no cytoplasmic
41
determined to give rise to specific parts of the embryo
definite blastomeres
42
type of cleavage in definite blastomeres
determinate cleavage
43
development of determinate cleavage
mosaic development
44
example of definite blastomeres
Ascaris egg
45
- embryo resembles mulberry
- blastomeres are in early cleavage stage
morula
46
- cleavage cells form the blastoderm epithelium enclosing blastocoel
- cells form gap and tight junctions
blastula
47
what junctions are formed in blastula stage
gap and tight junctions
48
- forms in merblastic cleavage
- yolk lies under the disc
blastodisc
49
peculiarities in mammalian cleavage
1. holoblastic rotational
2. slow division; asynchronous
3. embryo undergoes compaction
4. early expression of zygotic genes
50
stage of the egg inside the uterus dueing blastocyst stage
early stage implantation
51
gamete contains determinants which are apportioned differentially into blastomeres which develop nto different cell types
Weismann's germ plasm theory
52
contradicts Weismann's germ plasm theory
1. Spemann's expt on constricted newt zygote; 2 halves developed into normal embryos
2. In dragonfly, one of the first 2 nuclei of fertilized egg was irradiated, but a whole embryo still developed
3. cloning expts - first done on frogs
53
cloning
nuceli transplantation into enucleated and activated egg
54
had less success in cloning
nuclei from progressively differentiated/ adult donors
55
Factors determining fate of blastomeres
1. intrinsic
2. extrinsic
56
- differentation of cells are not traced to differences in nuclear components of each cell but difference in cytoplasmic components
- cytoplasm dictates
intrinsic
57
- what the blastomeres become may be dictated by surrounding blastomeres
- environment dictates
extrinsic
58
Supported the intrisic factors in differentation
1. Spemann's expt of egg constriction
2. Dentalium zygote
3. _Styela_ _partita_ zygote
4. Centrifugation experiments
5. germ plasm observation
59
normal embryos resulted in each half contained grey crescent
Spemann's expt of egg constriction
60
only blastomere D with clear cytoplasm from veg pole develop mesoderm
Dentalium zygote
61
comes from egg with cytoplasm clearly divided into 4, each with different fates
_Styela_ _partita_
62
Supported the extrinsic factors in differentiation
1. at early stage if future ICM and trophoblast cells are mixed, whatever locates inside becomes embryo and whatever is outside becomes trophoblast
2. concept of regulatory/indeterminate cleavage and determinate or mosaic pattern
63
products or proteins which affect the cells
morphogens
64
Morphogenetic gradient in egg cytoplasm:
Macromeres
from veg pole develop into ectoderm and endodermal structures
65
Morphogenetic gradient in egg cytoplasm:
Micromeres
from veg pole into larval skeleton or spicules
66
Morphogenetic gradient in egg cytoplasm:
Mesomere
from animal pole into most of ectoderm of larva
67
splitting of blastomeres into vegetal and animal pole cells cause what
- vegetalization or
- animalization of larva
68
experimented in the vegetalization or animalization of larva
Horstadius
69
vegetalizing agents
1. lithium ions
2. sodium axide
3. dinitrophenol
70
animalizing agents
1. acidic dyes
2. zinc
3. mercury
4. anionic detergents
5. some proteolytic enzymes
71
vegetalization might involve what
inhibition of oxidative enzymes which produce ATP
72
animalization might involve what
ability to attack proteins esp. basic proteins
73
determine the peculiarity of the egg in early development
cells of the maternal body
74
example of peculiarity of egg that is determined by genotype of mtoher
dextrality or sinistrality of freshwater snail (_Lymnea_ _peregra_)
75
- maternal inhertiance in lethal 'o; gene
- correctiv factor is found in the nucleus of normal egg
axolotl (_Amystoma_ _mexicanum_)
