At the bottom of page 128 the reader is instructed to add the following:

soln = Genetic.run(Schedule)
IO.write("\n")
IO.inspect(soln.genes)

and the output is given on page 129 as:

%Types.Chromosome{
age: 1,
fitness: 14.7,
genes: [0, 1, 1, 0, 1, 1, 1, 0, 0, 1],
size: 10
}

In order to get the output to look like this the IO.inspect(soln.genes) should be IO.inspect(soln) otherwise just the genes are printed.