Control of development Flashcards
What are the key stages of developement?
Fertilisation cleavage gastrulation organogenesis morphogenesis
What controls developement?
cytoplasm
genes
external environment
What does Nuclear DNA usually do that doesn’t occur in early developement?
Makes proteins by transcription, in early developement it only replicates
Where do proteins and enzymes come from in early development?
Provided for by the cytoplasm
Where does zygotic cytoplasm come from?
The mother, so early development under maternal control
What is genomic activation?
The transition from maternal control to embryo control
Timing of genomic activation varies among species, when does it occur for:
pigs?
humans?
frogs?
Pigs = in 4-8 cell embryo Humans = 8 cell embryo Frogs = 3000-4000 cell embryo
What are cells called prior to determination?
Totipotent
What causes differentiation to occur?
results from differential gene expression, which is influenced by the cytoplasm and extracellular environment
What is genomic equivalence?
Each cell in the body has same genetic material and therefore all the information necessary to create a complete organism
What controls the fate of the nucleus?
The cytoplasm
What is cytoplasmic segregation?
Occurs in division. Dividing cells receive a factor that is unequally distributed in the cytoplasm and ends up in some daughter cells but not others, causes differentiation on cells
What is induction?
A factor is secreted by some cells to induce other cells to differentiate
What are the processes of primary induction amphibians?
Cells moving over the dorsal lip of the blastopore (Spemann organiser) induce overlying ectoderm to form neural tissue
What are the processes of primary induction in birds?
Cells moving over Hensen’s node are induced to form the Central Nervous System
What is secondary induction?
Occurs after primary, includes the development of control in the vertebrate eye
What is a morphogen?
A chemical agent able to cause or determine morphogenesis
When is a signal called a morphogen?
When it directly affects a target cell or when different concentration cause different effects
Describe the process of limb formation
The cells that become the bones and muscles of a limb receive positional information, then organise appropriately. Cells at the bud make the morphogen BMP2
how does BMP2 control limb developement?
The gradient determines anterior-posterior axis, A high dose lead to thumbs, a low dose leads to the little finger
What is genomic imprinting?
Some genes are only active if they come from the sperm, some are only active if they come from the egg, which means male/male or female/female zygotes can’t form
What is Prader-Willi syndrome?
Deletion on the paternal chromosome 15
What is angelman syndrome?
Deletion on the maternal chromosome 15
What do segmentation genes do?
influence the number, boundaries and polarity of body segments
What do gap genes do?
Organise large areas along the anterior-posterior axis
What do pair rule genes do?
Divide the embryo into units of two segments each
What do segment polarity genes do?
determine segment boundaries
What do homeotic genes do?
expressed along the length of the body and determine what segments will become
What are hox genes?
A subset of homeotic genes that control the body plan of an embryo along the head-tail axis
What apoptosis?
Programmed cell death, cause by the activation of ‘death’ genes
How does the environment affect developement in house mice?
Gut bacteria induce gene expression in the intestine, which is essential for normal capillary development
What happens in humans as a result of neural tube failing to close?
At the posterior = spina bifida
At the anterior = anencephaly
What causes goitre and cretinism?
Lack of iodine in the diet
What does Cyclopamine cause?
Birth defects in lambs, found in corn lily plants, inhibits action of the sonic hedgehog protein which is involved in neural system formation
