Fa gray cat and a white cat have kittens, what phenotypes could the kittens exhibit?

Depends on whether the genes that code for grey fur or code for white for are dominant, which ever one is dominant will show the phenotype. Assuming grey fur is dominant over white it also depends on if the grey cat is carrying white fur genes as these genes will be passed onto the kittens and with the white genes as well you may get a mix of grey and white cats. usually a punnet square is used to show this type of scenario.

.G - dominant g - recessive
     G     G
g   Gg   Gg
g   Gg   Gg  

This punnet square shows what happens if the grey cat has only grey genes, all the kittens will be grey as they all carry the grey gene,

    G     g
g  Gg   gg 
g  Gg   gg 

This punnet square shows what happens if the grey cat is carrying white fur genes, because of the white gene being present, half of the kittens would be grey and the other half would be white, even though one of the parents was grey it produced half non grey offspring because it was carrying white fur genes 

Mitochondria is the cell organelle that produced the energy that is needed in the body system in form of atp, that is why it is called the power house of the cell. energy is needed by the living organisms to carry out the activities which sustain life.  if the mitochondria is destroyed atp will not be produced. if the mitochondria is destroyed, energy production will stop and the affected living organism will not have the energy to carry out the necessary life processes; this will lead to the death of the organism.