Development 1: Zygote to organism Flashcards
Define development
Series of progressive changes in form and function that occurs during an organism’s life cycle
What does development continue until?
Death
What are the 5 key stages of development?
- Fertilisation
- Cleavage
- Gastrulation
- Organogenesis
- Morphogenesis
What is fertilisation?
1 sperm enters egg.
- inside paternal and materinal genetic material fuse = diploid cell
- stimulates cleavage
Which parent do the cytoplasm and mitochondria of the zygote come from?
Mother
Which hemisphere is the nucleus in (in most species)?
animal hemisphere
Which hemisphere do nutrients accumulate?
Vegetal hemisphere
In what class does the ‘grey crescent’ appear?
Amphibians
Describe the grey cresent
- In amphibians sperm enters the animal hemisphere, the cortex rotates exposing the grey crescent
- Proteins in the grey crescent control what form the cells will take
What is cleavage?
Rapid series of cell divisions
What is each cell produced during cleavage called?
Blastomere
How many patterns of cleavage are there, and what are they?
Complete
Incomplete-discoidal
Incomplete-superficial
What does cleavage pattern depend on?
Species dependent:
- Depends on amount of yolk and orientation of spindles
Describe complete cleavage
No yolk = all cells are equal size e.g sea urchins
Yolk gets in the way of the cleavage furrow = cells divide asymmetrically e.g frogs
Describe incomplete cleavage - discoidal
- With lots of yolk the cleavage furrows don’t penetrate the yolk = cleavage is incomplete
- A blastodisc forms on top of the yolk
E.g birds
Describe incomplete cleavage - superficial
- Nucleus divides but cytokinesis doesn’t occur
- Nuclei migrate to the edge & membrane grows inward = nuclei partitioned into individual cells
E.g insects
Describe radial cleavage
mitotic spindles form at right angles/ parallel to animal- vegetal axis
Describe spiral cleavage
Mitotic spindles are oblique angles (diagonal) to a a-v axis
Describe rotational cleavage
first division is parallel to a-v axis, second is at right angles = ‘disorderly’ arrangement of daughter cells
Early in development cells can be described as ________
totipotent
define totipotent
any cell can become any cell type
What is determination
When a cells fate is fixed (fate map)
- cells become structurally and functionally specialised
What is gastrulation?
process where a blastula is transformed into an embryo with body axes and 3 tissue layers
→ one of the most important stages in development
What is the endoderm?
Inner layer - gastrointestinal tract, inc. liver, pancreas, and respiratory system
What is the mesoderm?
middle layer - bone, muscle, heart, kidneys, bladder, ovaries/testes and inner layer of skin
What is the ectoderm
outer layer of skin and nervous system
In birds and reptiles, where does the epiblast originate from?
The blastodisc
In mammals, , where does the epiblast originate from?
The inner cell mass
In birds, what are the epiblast and they hypoblast?
Epiblast → embryo
Hypoblast → extraembryonic membranes
In mammals, what is the yolk replaced by?
A placenta
What is organogenesis?
the formation of organs
What is neurulation and when does it occur?
Early in organogenesis begins the formation of the nervous system in vertebrates
Describe the 3 stages of neurulation
- Thickening of the ectoderm = neural plate
- Edges of neural plate thickens further, creates ridges
- Ridges fuse over the top = cylinder (neural tube)
Describe body segmentation
- Somites produce the vertebrae, ribs and muscles of the trunk and limbs
- Neural crest cells produce peripheral nerves
What are the 4 extraembryonic membranes in birds?
Yolk sac
Amniotic sac
Chorion
Allantois
What is the function of the yolk sac in bird eggs?
= nutrient transfer (through blood vessels)
What is the function of the amniotic sac in bird eggs?
= surrounds embryo and secretes fluid = protection
What is the function of the chorion in bird eggs?
= limits water loss & allows gas exchange
What is the function of the allantois in bird eggs?
= Sac stores metabolic waste
