Chapter 44: Animal Development Flashcards
Animal development
transformation from a single egg, zygote (diploid [2n] fertilized egg) via cell division, cell movement, cell specialization, pattern formation and apoptosis
What are the stages of development?
cell division–>cell expansion–>growth–>cell differentiation–>creation of tissue–>creation of organs
What are the 4 processes of development?
- determination
- Differentiation
- Morphogenesis
- Growth
Differentiation
the process by which different types of cells arise
Morphogenesis
organization and spatial distribution of differentiated cells
Growth
increase in body size by cell division and expansion
What are the ways in which morphogenesis occurs?
cell division, cell expansion, cell movements, apoptosis
Cell fate
which type of tissue the cell will ultimately become. cell fate is usually determined quite early
Fertilization
gametes, sex cells
Haploid
one set of chromosomes
Diploid
two sets of chromosomes
Gametes are produced when?
meiosis
how do the gametes get their chromosomes?
each parent contributes a set
How is zygote produced?
fusion of gametes
What is the human egg protected by?
cumulus and zona pellucida
what does fertilization do?
- blocks entry of additional sperm
- stimulates ion fluxes across membranes
- changes pH of the egg
- increases egg metabolism and protein synthesis
- initiates cell division
what is contained in eggs
large, well stocked with organelles, nutrients, transcription factors, and mRNA
Cumulus
keeps out unhealthy sperm
What happens during fusion?
2 pronuclei lose their nuclear membranes and fuse together to form diploid zygote
Vegetal hemisphere
lower half of egg, where nutrients are concentrated
Animal hemisphere
opposite end of the egg, has pigments and contains nucleus
Cleavage
blastula formation, cleavage in mammals is unique, specific blasters generate specific tissues and organs
Gastrulation
three germ layer formation
Organogenesis
formation of an organ system
Neurulation
formation of a nervous system
Mosaic development is
determinate
Regulated development is
indeterminate
Cleavage
early cell divisions with no cell growth. embryo becomes a solid ball of small cells.
Blastocoel
a central fluid-filled cavity that forms in the ball
Blastula
developed embryo
Blastomeres
the cells of the blastula
complete cleavage
eggs with little yolk
incomplete cleavage
occurs in eggs with a lot of yolk when cleavage furrows don’t penetrate
Discoidal cleavage
embryo forms as a blastodisc that sits on top of the yolk
Superficial cleavage
variation of incomplete cleavage in insects
Syncytium
cell with many nuclei
Why is there little increase in overall volume during cleavage?
because the blastomeres become progressively smaller
What influences cleavage?
amount of yolk, orientation of mitotic spindle,
Blastocyst
a dense inner cell mass on top of a hollow blastocoel, surrounded by a trophoblast
Mammalian cleavage is slow or fast?
slow and asynchronous
what happens when the zygote reaches the 8 cell stage?
blastomeres change shape and maximize contact with one another to form a tight ball
What happens at the 32 cell stage?
Inner cell mass- becomes the embryo OR trophoblast forms from outer cells
Trophoblast
sac that forms from the outer cells. its cells secrete fluid to create the blastocoel cavity, with the inner cell mass at one end.
Mosaic development
loss of blastomeres results in loss of later structures
Regulated development
loss of blastomeres does not deleteriously affect development because the remaining cells compensate for the loss (ex: in human blasters but not inner cell mass)
Mosaic development
each blastomere contributes certain aspects to the adult animal (roundworms) removing one blastomere will harm the embryo
Regulative development
other cells compensate for any lost cells (many vertebrates) one blastomere removed won’t harm embryo
Blastomeres
separate into two groups, each can become an embryo
Monozygotic twins
come from same zygote and are identical
Nonidentical twins
from two eggs fertilized by two sperm
Gastrulation
three germ layer formation - from hollow ball to tube within a tube
Gastrulation
formation of a gastrula
Gastrula
embryo with gut connected to outside by mouth or anus “opening”; a blastopore
Cells of blastula reorganize into how many layers?
three germ layers.
What are the three germ layers?
- Ectoderm
- Endoderm
- Mesoderm
Germ layers are fated to develop into specific adult tissues
“determined” to develop this way … later develop into specific tissues through differentiation
Ectoderm
fates include nervous system and epidermis of skin
Endoderm
fates include inner linings of gut and respiratory system, liver, pancreas, urinary bladder
Mesoderm
becomes the skeletal system, circulatory systems, kidneys, gonads, blood cells, muscles, dermis of skin
What does Gastrulation form
the gastrula: an embryo with an internal cavity “primitive intestine”
Invagination
creates a primitive intestinal cavity (archenteron) exposed to the outside through the blastopore that later forms either an anus or mouth depending on organism
Deuterosomes
blastopore forms anus, mouth later forms from second opening
Protosomes
blastopore forms mouth, anus later forms from second opening
Gastrulation in the Bird: what happens to blastoderm cells?
they migrate to the primitive streak, move through it into the blastocoel to form the endoderm and the mesoderm
Blastula in the birds
flat disk of cells on top of the yolk
Hypoblast
a continuous layer that will contribute to extra embryonic membranes, formed from cells that enter the fluid space between blastodisc and yolk
Epiblast
overlying cells that will become the embryo, move toward the midline and form a ridge called the primitive streak
Hensen’s node
equivalent of the amphibian dorsal lip and contains many signaling molecules.
Trophoblast:
that layer surrounding the blastocoel
Where does fertilization occur in mammals?
oviduct; cleavage occurs as the zygote travels down oviduct to uterus
Implantation: when does it occur?
when the trophoblast adheres to the endometrium (uterine lining)
Ectopic (tubal) pregnancy
implantation occurs in the oviduct: zona pellucida usually prevents this
blastocyst
the cell mass that is implanted in the maternal uterus
Trophoblast
outer layer of the blastocyst that becomes the placenta
Determination
influenced by gene expression and the extracellular environment. it’s a commitment.
Differentiation
changes in biochemistry, structure, and function that result in different cell types
Cell potency
potential to differentiate into other cell types
Totipotent
can differentiate into any cell type (early embryo)
Pluripotent
can develop into most cell types, but cannot form new embryos
Multipotent
can differentiate into several related cell types
Unipotent
can produce only one cell type: their own (mature organism)
Organogenesis
the making of organs
Chordamesoderm
the mesoderm closest to the midline
Notochord
provides support for the embryo
What does the chordamesoderm do?
has organizer functions and induces the ectoderm to form the nervous system
Neurulation slide 54 & 56
forming of nervous system; process by which external sheet of cells (neural plate) develops into an internal tube (neural tube) that later develops into brain and spinal chord
Chordates
- Invertebrates
2. Vertebrates
What are some examples of invertebrates?
tunicates and branchiostoma
What are some examples of vertebrates?
fishes, reptiles, mammals, amphibians, birds, humans
somites
blocks of mesodermal cells that produce cells that become the vertebrae, ribs, muscles, and lower skin layer. ; guide peripheral nerve development
Determination
germ layers are fated to develop into specific tissues through differentiation
- cytoplasmic segregation
- embryonic induction
Determination by cytoplasmic segregation
cytoplasmic components of eggs are unevenly distributed into separate cells or parts of cells to cause cell determination
Determination by embryonic induction
interactions with other cells/tissues causes determination. the inducer is the specific chemical signal
Is the fate of a cell in the early embryo already determined?
Cell fates in the early embryo are not determined, but can change depending on the environment
Do different regions in the fertilized egg and the embryo have different developmental potential?
the animal and vegetal pole halves differ in their developmental potential
Cytoplasmic segregation, aka
unequal cytokinesis
Induction
cell-to-cell communication
cytoplasmic segregation
factors within a zygote or egg are not distributed evenly and end up in different daughter cells after division; polarity with a top and bottom
Animal development: which is top and which is bottom/
animal pole=top
vegetal pole=bottom
What happens if a sea urchin an eight-cell embryo is cut vertically?
develops into 2 small larvae
What happens if a sea urchin eight-cell embryo is cut horizontally?
bottom develops into larva, top remains embryonic
Are cytoplasmic factors necessary for development localized in the fertilized egg?
cytoplasmic factors in the gray crescent are crucial for normal development
When is presumptive epidermis determined to follow a particular developmental path?
during gastrulation, presumptive neural ectoderm becomes determined to develop into nervous system
Can some cells induce other cells to follow a particular developmental path?
the dorsal lip can induce other cells to participate in embryogenesis
