Principles of Development ch 8 Flashcards
What are the stages in animal developement?
1.Gamete formation
2. Fertilization
3. cleavage
4. gastrulation
5. Organogenesis
6. growth
Gamete formation
Sperm and eggs form, mature
Fertilization
the union of male and female gametes to form a zygote
Cleavage
a series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller, nucleated cells.
Gastrulation
-converts the spherical blastula into a two- or three- layered embryo
-Germ layers form
establish body plan
What is a hollow ball of cells called?
blastula
Cleavage subdivides the mass of the zygote until a cluster of cells called a __________
Blastula
Prior to fertilization egg accumulates yolk & contain ________ ____________such as transcription factors and inducing factors, that switch genes on or off following fertilization.
Morphogenetic
Determinants
Entrance of more than one sperm, called ________, must be prevented because union of more than two haploid nuclei would be ruinous for normal development. Entrance of more than one sperm produces a polyploid egg nucleus, which cannot undergo normal division: more than two mitotic spindles form, so chromosomes are unevenly di- vided among daughter cells.
polyspermy
Fast block
- change membrane potential-contact of the first sperm with the egg membrane is instantly followed by an electrical potential change in the egg membrane that acts as a transient electrical barrier to pre- vent additional sperm from fusing with the membrane
what comes first, fast block or slow block?
fast block
slow block
- cortical reaction; form fertilization membrane
-a cortical reaction in which thousands of enzyme-rich cortical granules located just beneath the egg membrane fuse with the membrane and release their contents into the space between the egg membrane and the overlying vitelline envelope
zygote
- fused egg + sperm
-fertilized egg cell that results from the union of a female gamete (egg, or ovum) with a male gamete (sperm)
cleavage
a series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller, nucleated cells.
Single cell (zygote) divides into many cells (blastomeres)
cleavage
Blastula
hollow ball of cells
Blastocoel
fluid filled space in center of a blastula
is a blastula a single cell?
no it is many cells
cleavage planes
at 90°; blastomeres lie atop each other
radial cleavage
cleavage planes
at 45° angle; blastomeres lie in
cleavage furrows
Spiral Cleavage
divide completely
through the egg
Holoblastic cleavage
When little yolk is present, cleavage furrows extend completely through the egg in _________ _________
holoblastic cleavage
the cleavage furrow does not completely divide the cytoplasm of the egg at each cell division. When much yolk is present, cleavage is__________ , with cells sitting atop a mass of undivided yolk
meroblastic
____________ converts the spherical blastula into a two- or three- layered embryo.
Gastrulation
Archenteron
primitive gut
-the cavity within an embryo at the gastrula stage of development that eventually becomes the digestive cavity.
Blastopore
opening for gut
Diploblastic
2 tissue layers
ectoderm and endoderm
ectoderm
outer layer
endoderm
inner layer, lines gut
what is a blastopore mouth called?
Protostome
what is a blastopore anus called?
Deuterostome
Triploblastic
3 tissue layers
ectoderm, mesoderm, and endoderm
Acoelomate
no body cavity; mesoderm fills
blastocoel
Animals without a coelom are called what?
acoelomate
Pseudocoelomate
mesoderm partially fills
blastocoel; lines ectoderm
-organisms that have false body cavities
Coelomate
body cavity is
completely surrounded by
mesoderm
After Coelom Formation:
3 tissue layers: ectoderm, mesoderm, endoderm
2 body cavities: gut cavity & fluid filled coelom (body cavity)
Cytoplasmic Specification
The cytoplasm of a fertilized egg is not homogeneous. It contains unequally distributed morphogenetic components such as mRNAs and proteins, which act as enzymes or as transcription factors. These components may be tethered to the cytoskeleton. As cleavage pro- ceeds, the mRNAs and proteins are unequally partitioned among the resulting new cells (blastomeres). Thus, the fate of each cell is spec- ified by the type of cytoplasm it acquires in cleavage, and even iso- lated cells differentiate along the path dictated by the cytoplasmic components. Cytoplasmic specification, sometimes called autono- mous specification, causes mosaic development of the embryo. The term “mosaic” is used because the embryo appears to be a composite of independently developing parts rather than of interacting parts
Conditional Specification (Induction)
What a cell becomes depends upon its position in the embryo. Its fate is determined by interactions with neighboring cells.
_______________ _____________ leads to regulative development; early blastomeres can be separated and form a complete individual
Conditional specification
How is cytoplasmic specification different from induction?
-cytoplasmic specification
Each cell with different instructions, Most Protostomes
-induction
Early blastomeres not fated
Deuterostomes
Protostome vs. Deuterostome Development
Protostome:
spiral cleavage, mosaic, blastopore=mouth, Enterocoelous
Deuterostome:
radial cleavage, regulative, blastopore= anus,
Schizocoelous
8.9 Name the derivatives of ectoderm, endoderm, and mesoderm.
Ectoderm: Skin, hair, nails, Nervous system
Mesoderm: Circ. System, Line body coelom, Somites (bone & muscle)
Endoderm: Respiratory tract, Gut tube, Liver, pancreas
How do cells get committed to their fate?
– Cytoplasmic Specification
– Conditional Specification (Induction)
8.7 What is the importance of homeotic genes in animal development?
specifying cell identity and positioning during embryonic development
