Question

Out of the two repeated steps in EM algorithm, the step 2 is ________

(a) the maximization step

(b) the minimization step

(c) the optimization step

(d) the normalization step

The question was asked in a national level competition.

My question is based upon Statistical Methods for Aiding Alignment in chapter Multiple Sequence Alignment of Bioinformatics

Answer 1

Right choice is (a) the maximization step

To elaborate: In step 2, the maximization step, the new counts of bases or amino acids for each position in the site found in step 1 are substituted for the previous set. Step 1 is then repeated using these new counts. The cycle is repeated until the algorithm converges on a solution and does not change with further cycles. At that time, the best location of the site in each sequence and the best estimate of the residue composition of each column in the site will be available.