Question

In a hypothetical embryo, cell A divides to produce two daughter cells, X and Y. Within half an hour of this division, X begins expressing mRNAs characteristic of endoderm whereas Y does not.

a) [8pts] Explain in general terms (no specific names required) two ways that this difference between X and Y could have arisen.

b) [4pts] Is cell X determined to become endoderm at this time? Explain your answer.

Answer 1

a) Determination of cell to particular fate can be Specified (Committed) or Determined depending uon the molecular signals. If a cell A produce two daughter cell , X and Y. Within half an hour of division, X begin to express mRNA of endoderm whereas Y doesn't. There could be two possible reason for such unequal expression: may be some signals are missing in Y that restrict the cell to determine its fate or some external molecular signal receive in X in the form of either protein, RNAs or surface interaction that result X expressing mRNA characterstic of endoderm.

b) Since the X begins expressing mRNA characterstic of endoderm so its fate has been determined to form endoderm only (the innermost germ layer) which subsequently give rise to gut and internal organs such as liver, lungs, pancreas etc.