What Controls Development? Flashcards
What controls development?
Cytoplasm
Genes
External environment
What was the Spemann Experiment?
Cut two salamander zygotes differently
If both segments got some gray crescent, both develop into fully formed adults
If only one segment gets the gray crescent then only the one with it turns into a fully formed adult
Conclusion = cytoplasmic factors in gray crescent are necessary for development
What is genomic activation?
The transition from maternal control to embryonic control
Timing varies by taxa
What is genomic equivalence?
No information is lost in early stages of embryonic development
What is cytoplasmic segregation?
Dividing cells receive unequal amount of material that were distributed unevenly in the zygote
What causes cell differentiation?
More material at vegetal pole
Bottom cells would give different signals than the top ones
What is primary induction in amphibians?
Cells moving over dorsal lip of the blastopore (Spemannn Organiser)
Induces overlaying ectoderm to form neural tissue
What is primary induction in birds?
Cells moving over Henson’s node are induced to form CNS
What is secondary induction in vertebrate eye?
Forebrain bulges out to form optic vesicles
Signals from vesicles induce surface tissue to form lens placo tissue
Tissue gives rise to sensory organs
Tissue differentiates into lens
As it differentiates it influences optic cup and cornea formation
What makes something a morphogen?
Directly affects target cells
Different concentrations cause different effects
What causes positional information?
Given by the concentration gradient of a morphogen
What genes establish body segmentation and how?
Gap genes = organise large areas along anterior-posterior axis
Pair rule genes = divide embryo into units of two segments each
Segment polarity genes = determine segment boundaries
Homeotic genes = expressed along length of the body and determine what segments will become
What do segmentation genes influence?
Number, boundaries and polarity of body segments
What do Hox genes control?
Control differentiation along body axis
Where is Hoxb1 expressed?
Anterior part of the hindbrain
How are Hox genes expressed?
First Hox gene expressed most anterior and last gene expressed most posterior
What is antennapedia?
Legs grow instead of antennae
What is bithorax?
Extra thorax so has two sets of wings
What causes spina bifida?
Failure to close at posterior end during neurulation
What causes anencephaly?
Failure to close at anterior end during neurulation
What does lack of iodine cause?
Goitre in adults
Cretinism in babies
How many somatic cells are programmed to die in C.elegans
131
What stimulates apoptosis between human fingers and toes?
Capsase enzyme
What is genomic imprinting?
Some development genes are only active if they come from sperm, others from eggs
What do female genes control?
Embryo
What do male genes control?
Trophoblasts and the placenta
How do limbs develop?
Develop from limb bud
Cells receive positional information then organise appropriately
Cells at the base of the limb bud make the morphogen BMP2
BMP2 gradient determines anterior-posterior limb axis
Highest BMP2 dose = thumb
Smallest BMP2 dose = little finger
