Your code is telling it to assign [rand,0] to gene(M). This means that it will always assign the value to the 10th row, which is what it looks like it is doing. You are assigning correctly for fitness, and you can see the values of Gene change each time since the values for fitness are different in every row.
Did you mean to use k instead?
M = 10; %no of chromosomes (candidate solutions)
for k = 1 : M
population.Chromosomes(k).Gene = [rand, 0];
end
And now to visualize the results.
population.Chromosomes.Gene
