Introduction to Development Flashcards
What is development?
A series of progressive changes in form and function that occurs during an organisms life cycle
What are the key stages of development?
Fertilisation
Cleavage
Gastrulation
What are the main steps of fertilisation?
One sperm enters the egg
Maternal and paternal genetic material fuse to form a diploid cell
Stimulates cleavage
What are the main points of cleavage?
Rapid series of cell division
Produces blastomere
Cells move towards the edge to form a blastula
3 patterns of cleavage
What do the cleavage patterns depend on?
Amount of yolk and spindle orientation
What are the three cleavage patterns?
Complete
Incomplete - discoidal
Incomplete - superficial
How does complete cleavage work?
No yolk = cells divide evenly top to bottom in equal size
Yolk = yolk impedes cleavage furrow and so cells divide asymmetrically and get different sized cells
How does incomplete discoidal cleavage work?
Lots of yolk so cleavage furrows don’t penetrate
Blastodisc forms on top of the yolk and forms a membrane
How does incomplete superficial cleavage work?
Yolk in the middle
No cytokinesis but get nuclei division
Nuclei migrate to outer edge
Membrane forms around each individual nuclei to form individual cells
What is the definition of gastrulation?
Blastula is transformed into embryo with body axis and three tissue layers
What are the three tissue layers in gastrulation and what do they form?
Endoderm (inner layer) = gastrointestinal tract and respiratory system
Mesoderm (middle layer) = bone, muscle, heart, kidneys, bladder, reproductive organs and inner skin layer
Ectoderm (outer layer) = outer layer of skin and nervous system
How do mitotic spindles attach on radial cleavage?
Spindles form at right angles or parallel to animal-vegetal axis
Forms a regular blastomere pattern
How do mitotic spindles attach on spiral cleavage?
Spindles are at oblique angles to a-v axis
Get spiral blastomere pattern
How do mitotic spindles attach on rotational cleavage?
1st division = parallel to a-v axis
2nd division = right angles
Get disordered/rotational pattern
What is organogenesis?
Formation of organs and organ systems
Get development of body segments
What do somites produce?
Vertebrae, ribs, trunk and limb muscles
What do neural crest cells produce?
Peripheral nerves (connect to spinal cord)
What is neurulation?
Occurs in early organogenesis
Begins formation of nervous system in vertebrates
Basics of neurulation?
Ectoderm and neural plate thicken
Ridges on neural plate form
Forms a groove
Ridges fuse over top to form a neural tube
What are the basics of gastrulation in mammals?
Blastula forms trophoblasts and inner cell mass
Trophoblasts form placenta
Inner cell mass forms epiblast and hypoblast
Epiblast forms future embryo
Hypoblast forms extra embryonic membranes
Epiblast and hypoblast formed in blastocyst
Blastocyst implants itself into uterus
What are the basics of gastrulation in birds?
Starts when Henson’s node moves anterior to posterior - gives brain longer to develop
Movement down body axis forms primitive streak
Cells migrate to primitive streak
What are the basics of gastrulation in sea urchins?
Blastomere invaginates
Primary mesenchyme cells migrate to invagination
These become mesoderm cells
Then become archenteron
Secondary mesenchymal cells attach to archenteron and pull it up
Mouth forms at blastopore
What are the importance of extra embryonic membranes in birds?
Support the embryo
Develop from germ layer
Yolk sac = for nutrient transfer via blood vessels
Amniotic sac = outer layer which provides protection
Chorion = for gas/water transfer and limits water loss
Allantois = stores metabolic waste
