Development 2: What controls development? Flashcards
What are the 3 control factors in development?
Cytoplasm (epigenetic)
External environment (epigenetic)
Genes (genetic)
During embryonic development, what normal DNA process is ‘turned off’?
Transcription
What is the cytoplasm’s role in embryonic development?
Controls metabolic cycles and instructions for driving cell division
Early development is controlled by which parent?
Maternally controlled, cytoplasm comes from mother
What is genomic activation?
change from maternal control to embryo control
Describe what happens once genomic activation has occurred.
- Embryonic DNA starts transcription = cell division
- Cell division slows down (because transcription & translation take time) = how this stage is identified
What does cell differentiation result from?
differential gene expression (certain genes are switched off = cell function)
What is differential gene expression influenced by?
the cytoplasm and the extracellular environment
Describe the results of the Experiment on frogs to test the role of cytoplasm on differentiation
Genomic equivalence = No info is lost in the early stages of development (every nucleus in every somatic cell contains all the genes for creating a whole new individual)
= Shows the cytoplasm controls the fate of a nucleus
Describe cytoplasmic segregation in development
when a factor is unequally distributed in the cytoplasm and ends up in some daughter cells but not in others, or in greater conc.s than in others
= cause differentiation of cells due to animal and vegetal poles differing in their developmental potential
Define induction in development
When a factor is secreted by some cells to induce others to differentiate
Describe primary induction in birds and amphibians
- In amphibians, cells moving over the dorsal lip of the blastopore (Spemann organiser) induce overlying ectoderm to form neural tissue
- In birds, cells moving over Hensen’s node are induced to form the CNS
The development of which sensory organ is an example of secondary induction?
the vertebrate eye
How do cells ‘know’ where they are in an animal?
By interpretating positional info = conc. gradient of a morphogen
A signal is a morphogen if …
- It directly affects target cells (does not work through an intermediary)
- Diff conc.s cause different effects
What is genomic imprinting?
in mammals some development genes are active only if they come from a sperm OR egg
What are segmentation genes?
they influence the number, boundaries, and polarity of the body segments
What do gap genes do in body segmentation?
organise large areas along the anterior large areas along the anterior-posterior
What do pair rule genes do in body segmentation?
divide the embryo into units of 2 segments each
What do segment polarity genes do in body segmentation?
determine segment boundaries
What do homeotic (hox) genes do in body segmentation?
are expressed along the length of the body and determine what the segments will become
Describe how body segmentation is controlled in mice
- 4 families of homeotic genes (hox genes) control differentiation along the axis
- Temporal and spatial pattern of expression of hox genes is tied together → also follows the linear order on the chromosome
How do hox genes control segmentation? What do mutations result in?
they specify the properties of each segment, mutations in these can change a segments identity
What is apoptosis?
programmed cell death, caused by the activation of ‘death’ genes
Give an example of apoptosis in human development
In development, we have webbed hands and feet - the enzyme caspase stimulates apoptosis of this extra skin
Give en example showing why environmental factors can be necessary for successful development
House mice raised in microbe-free environments lack gut bacteria
- Gut bacteria induce gene expression in the intestine which is essential for normal capillary development
Give an example of environmental factors disrupting development
Cyclopamine inhibits the action of the Sonic Hedgehog protein, which is involved in the formation of the neural system
Give an example of a developmental stage that is under both genetic and environmental control
Neurulation: primarily under genetic control, but environ derived material e.g vitamins and minerals are also needed
= neural tube defects can be reduced if the pregnant person receives enough folic acid
