The method used here is agarose gel elecrtrophoresis in which DNA ladder is used which is a set of standard used to determine the size of DNA used .The DNA ladder is put adjacent to the DNA fragments to be visualized Suppose if the ladder shows 300 basepair so the DNA adjacent to this number will be of this size.These are the set standards used to determine the size of DNA or RNA. For a range we can take 2% of agrarose to run DNA fragments upto 500 Basepair. Most of the amplified DNA falls into this category size.
The answer is 1). Two Tt parent can produce T and t for 50% separately. So for the result, TT has the probability of 50%*50%=25%. The same for tt. And Tt is 1-0.25-0.25=50%.
