Animal Development Flashcards
When haploid gametes dude, what is produced?
A diploid zygote
What are the 3 initial processes through which a gamete becomes a zygote which becomes a whole animal?
Fertilisation
Cleavage
Gastrulation
What is cleavage?
Cell division
What is gastrulation?
Cell / tissue movement and organisation
What does morphogenesis mean?
Making form
What is the name for multiple fertilisation of an egg?
Polyspermy
How is polyspermy prevented after fertilisation? (Describe the 2 ways)
Fast block to polyspermy - an electrical response of the plasma egg membrane, preventing a second sperm fusing with the membrane
Slow block to polyspermy - critical granules fuse with the egg’s plasma membrane, releasing their contents. Enzymes separate the plasma and vitelline membranes. Mucopolysaccharides cause water to enter the peri-vitelline space, physically separating the two membranes. The contents harden
When the vitelline membrane is separated from the plasma membrane with hardened contents between them, what is the membrane now called?
Fertilisation membrane
What two things are eggs surrounded by?
Jelly coat
Vitelline membrane/envelope
What is the acrosomal reaction?
When sperm makes first contact, the acrosome discharges it’s contents by exocytosis, Hydrolytic enzymes are released which allow the acrosomal process to penetrate the egg’s jelly coat. The plasma membranes of the sperm and egg fuse, so the sperm contents can enter the cytoplasm of the egg
At the beginning of cleavage, what does the egg divide into?
Nucleated blastomeres
No increase in embryo size
After a nucleated blastula, what is the 33 cell stage called?
Morula (solid ball of cells)
What does a morula then form?
Blastula
What is a blastula and what is the fluid-filled cavity inside it called?
Animal embryo when it is a hollow ball of cells
Blastocoel
How is cleavage accomplished?
By abolishing the growth period between cell divisions (G1 and G2 phases of the cell cycle)
What is different about cleavage in insects?
There is no cell division, only nuclear division
What 3 types of tissue become evident in gastrulation?
Endodermal
Ectodermal
Mesodermal
Which types of tissue move inside the embryo?
Endodermal and mesodermal
Which type of tissue remains external to the embryo?
Ectodermal
What is invagination?
Cells turn inside out or fold back on themselves to form a cavity
Which type of cells invaginate in the blastula?
Endodermal
Once the embryo is 2 layers of cells thick, what is it called?
Gastrula
What is the interior space of the gastrula called?
Archenteron
What is the point of invagination of endodermal tissue called?
Blastopore
What does the internal endoderm eventually form?
Gut and associated organs
What does the ectoderm eventually form?
Epidermis and central nervous system
What does the mesoderm eventually form?
Muscle, circulatory system, reproductive organs, skeleton
What is the mesoderm essential in the formation of?
The coelom (body cavity)
What are animals with 3 tissues called?
Triploblastic
What are animals with 2 tissues called?
Diploblastic
If the blastopore forms the anus, what is the animal called?
Deuterostome
If the blastopore forms the mouth, what is the animal called?
Protostome
What type of cleavage do protostomes show?
Spiral cleavage (diagonal to vertical axis) Determinate cleavage (fate set early)
What type of cleavage do deuterostomes show?
Radical cleavage (parallel and perpendicular to vertical axis) Indeterminate cleavage (fate set late)
What does determinate cleavage cause?
A loss of development potential, as the cells maintain their differentiation fate regardless of their location
What is neurulation?
The folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube
What is the notochord?
A longitudinal flexible rod between the gut and nerve cord, providing skeletal support
What tissue is the origin of the notochord?
Mesoderm
What is the neural tube and how is it formed?
It becomes the brain and spinal cord
It is formed by induction
What is induction?
Where a group of cells/tissues influence the development of another group through close-range interactions
What is the neural crest?
It will form the brain and parts of sensory organs anteriorly and other structures posteriorly
What is caused if the neural tube fails to close?
Spina bifida (leg paralysis)
What forms from plate of dorsal ectoderm?
The neural crest, neural groove and neural plate
What are the four extraembryonic membranes formed from the blastodisc?
Yolk sac
Amnion
Chorion
Allantois
What is the amnion?
A membrane above the ectoderm
What does the chorion develop from?
The trophoblast (the outer layer of cells of a blastocyst)
What is the allantois?
An outpocket of embryo gut, which later becomes incorporated into the umbilical cord
What causes changes in cell shape during tissue invagination?
The action of microtubules (made of tubulin) and actin filaments
How do cells move during gastrulation/neurulation?
They cytoskeleton extends the cell causing it to move
What is convergent extension?
The tissue of an embryo is restructured to converge (narrow) along one axis and extend (elongate) along a perpendicular axis by cellular movement
How is cell adhesion achieved?
It is controlled by the extracellular matrix (ECM)
What is the extracellular matrix (ECM)?
A mixture of secreted glycoproteins which act to guide cells. ECM fibres can act as tracks to direct movement
How is migration via the extracellular matrix blocked?
Antibodies added to fibronectin (a component of ECM)
What is an example of an adhesion molecule that holds cells together?
Cadherin
Adheres junctions to bind cells within tissues together
How can cell movements through an embryo be traced?
Antibodies bound to cellular markers are used
As an embryo develops…
The development potential reduces
The fate of every cell is determined by…
Gene expression
How was animal cloning achieved?
By reversing the determination of a differentiated cell
Asymmetrical division during cleavage leads to…
Asymmetrical distribution of cytoplasmic determinants
How is cell-cell induction possible?
The signals used may be molecules attached to the cell membrane or locally-diffusing molecules
What are the three sections of the common fruit fly?
Head
Thorax
Abdomen
How does cleavage occur in fruit flies?
Only nuclei divide, then they migrate to the periphery of the embryo and become secondarily separated by membranes
What are maternal effect genes?
Genes in the mother of an organism, which determine the characteristics of the offspring
What is an example of a maternal effect protein in fruit flies?
Bicoid protein
Transcribed from DNA of mother, not offspring themselves
How does bicoid protein affect offspring?
Bicoid mRNA accumulates at anterior end of egg and is transcribed. Diffuses through embryo, providing gradient for morphogenesis
If no bicoid protein is produced, how does the offspring develop?
With two posterior ends and no anterior end
When bicoid is injected into a bicoid mutant, what happens?
The anterior pole is re-established
What is bicoid an example of?
Transcription factor - it controls the transcription of other genes
What are gap genes?
They are vital in the formation of organisms with segmented bodies. Each gene is responsible for one segment
What are examples of gap genes?
Kruppel and Hunchback
What can inhibit gap gene translation?
Maternal effect gene products
What are pair-rule genes?
A specific region of every other segment is missing if one of these genes mutates
What controls the expression of pair-rule genes?
Differing concentrations of gap gene proteins, as they encode transcription factors controlling pair-rule gene expression
What is an example of a pair-rule gene?
Hairy
What are segment polarity genes?
These control the anterior and posterior polarity of each segment in organisms. They are expressed after gap and pair-rule genes have been expressed
What is an example of a segment polarity gene?
Engrailed
What are homeotic genes?
These determine the identity of each segment of the fruit fly
What is a subset of homeotic genes?
Hox genes
What are hox genes vital in?
Determining embryonic development along the axis of the embryo
What is the protein product of a hox gene?
Homeodomain
What is a homeodomain?
A DNA binding region which binds to the specific regulatory proteins of target genes and begins transcription of these genes, which are necessary for the correct development of the segment
How long is the homeodomain and how many helices does it consist of?
180 base pairs
4 helices
What order are homeotic genes found on the chromosome?
In the same order that they must be on the insect itself
What is the difference in placement of homeotic genes in vertebrates compared to insects?
In vertebrates the genes are found in different chromosomes
In animals, homeotic genes are…
Highly conserved (remain the same for long periods of time)
