Lecture 14 - Developmental Genetics Flashcards
(12 cards)
What is polarity at an organism-level based on?
Polarity at a cellular level
How are patterns assembled?
Cell proliferation is usually mitotic cell division. This leads to the development of clones - the progeny cells are all identical to parental cells. Multicellular organisms require cell specialization. This is associated with interactions between cells - environment can determine your developmental trajectory. Cell movement is different is different in plants, in which any changes are determined by changes in cell expansion & cell division angles.
What is cell fate determination?
Cell fate is the process of a cell acquiring a specialized fate/identity. This can occur through 1 division cycle through differentiation, but can also occur through lineages.
How can asymmetric division lead to cell fate determination?
INTRINSIC FACTORS
- these are typically found very early in development or in early in developmental lineages
- the determinants changing the fate of the progeny can be a metabolite, a signalling molecule, a transcription factor etc. Prior to cell division, this intrinsic factor is polarized with the cell. The cell division plate occurs to ensure that the particular molecule/component is inherited differentially by the 2 progeny cells, resulting in the deviation in the fate of the 2 cells.
EXTRINSIC FACTORS
- This will be cell communication (cells in contact with each-other) or components that are secreted by neighbouring cells, which influence the developmental outcome of the 2 progeny cells.
These are 2 ways in which 2 progeny cells can be made to divert in their developmental journeys.
This can also occur through LATERAL INHIBITION
What is lateral inhibition?
there is a component in a cell that inhibits its production of itself in a neighbouring cell. This causes amplification of level of transient bias between the 2 cells.
2 cells interact to regulate each other’s fates. “all or none situation”.
How is complexity developed?
This can be done by increasing the number of connections between cells.
What is a morphogen?
A morphogen is a signalling molecule that acts directly on cells to produce specific cellular responses depending on its local concentration.
Morphogens act over long distances & their local concentrations influence developmental decision.
How do morphogen concentrations vary?
There can be a concentration gradient of morphogen. There can also be a concentration gradient on inhibitor of morphogen. This is done by altering the density of the receptors. You can also change the way morphogens are processed - e.g. post-translational modification, cleavage or the way it is internalized.
Morphogen concentration is not key, but MORPHOGEN ACTIVITY
How are transcription factors influence pattern assembly?
TFs bind to elements within DNA, promoters& enhancers of target genes. TF will have a particular binding - e.g. 6-12bps. The more deviation from that ‘consensus’ sequence, the weaker the binding site.
High affinity site = lots of binding (e.g. even at low concentration binding is still found).
Low affinity site = lots of TF needed to bind.
How can gene regulation be complex?
Combination of different of morphogenic transcription factor & repressor transcription factor & different affinity binding sites for both can lead to different genes being transcribed.
Describe the makeup of Drosophila
3 thoracic sections - particular organs associated with these segments - e.g. legs (only 2nd thoracic segment has wings). One of the homeotic mutants has more than one.
Abdominal segments as well.
Good alignment between Larvae & adult Drosophila, which was good for development biologists.
What occurs with mutants in Drosophila development?
A number of mutants generated will be lethal, as they impact core developmental process. Studying a recessive mutant, & it is lethal, then it needed to be in a homozygous state. However, to study this but its lethal, so need to maintain a population of relevant chromosomes & mutants, otherwise will lose access.
BALANCER CHROMOSOMES developed & are chromosomes - e.g. chromosome 1 - and they have gone major rearrangement - e.g. inversions, translocations etc. This means balancer chromosomes usually have the full complement of the genes of the chromosomes, but because the order has been changed, they can’t recombine with the normal chromosome. Also need a marker to allow you to follow a chromosome through generations.
