13.2. Determination and Cloning Flashcards
Determination experiments…
Wilhelm Roux, frog development:
- Took a hot needle to kill one of the cells in the two-cell stage of a fertilised frog egg.
- He followed the growth of the egg cell and found the other half of the embryo develops into half an embryo.
- He concluded that the first determination occurs very early in development.
Hans Driesch, sea urchin development:
- He shook a two-cell sea urchin larva until one separated.
- One of the separated cells usually died, but development still resulted in a small, but normal larva.
- He concluded that determination does not occur at the two-cell stage, but at the eight-cell stage instead.
- When he separated the eight-cell embryo vertically, two small but normal larvae were produced. When he separated the eight-cell embryo horizontally, the top cells remained embryonic but the bottom cells produced abnormal larva.
Cytoplasmic segregation…
Factors in the cytoplasm (proteins / mRNA) become unequally distributed between daughter cells when the cell divides.
As the cell divides, different parts have even more unequally distributed factors - determining cell fate.
Induction…
Factors secreted by nearby cells can often influence cell fate.
This must be over a certain threshold to have any effect.
A high concentration may activate a transcription factor that triggers the cascade of cellular differentiation.
Cloning plants…
Mature plant cells can be induced to dedifferentiate to a totipotent state.
Dedifferentiated totipotent cells can form an entirely new, genetically identical plant copy, through cloning.
Cloning animals…
This is done through somatic cell nuclear transfer.
Remove the nucleus from an egg cell and fuse this with a somatic cell nucleus, causing the nucleus to revert back to the totipotent state.
No information is lost from nuclei of cells, which means they are genomically equivalent.
The cytoplasmic environment around the nucleus determines its fate, as it grows like a fertilised egg.
