Hamming distance

Today’s post will be about hamming exercise. This exercise can be found on: Exercism.io. First two task were very simple and I will not bother anybody with them but the hamming exercise was very nice to learn something new. About this exercise: … put in two lengths of DNA and calculate their hamming distance.
Following is the README file or basics instructions of the exercise:

Write a program that can calculate the Hamming difference between two DNA strands.

A mutation is simply a mistake that occurs during the creation or copying of a nucleic acid, in particular DNA. Because nucleic acids are
vital to cellular functions, mutations tend to cause a ripple effect throughout the cell. Although mutations are technically mistakes, a very
rare mutation may equip the cell with a beneficial attribute. In fact, the macro effects of evolution are attributable by the accumulated 
result of beneficial microscopic mutations over many generations.
The simplest and most common type of nucleic acid mutation is a point mutation, which replaces one base with another at a single nucleotide.

By counting the number of differences between two homologous DNA strands taken from different genomes with a common ancestor, 
we get a measure of the minimum number of point mutations that could have occurred on the evolutionary path between the two strands.

This is called the 'Hamming distance'.

It is found by comparing two DNA strands and counting how many of the nucleotides are different from their equivalent in the other string.

^ ^ ^  ^ ^    ^^

The Hamming distance between these two DNA strands is 7.

In my solution, first I split DNA strand into an array due to the each_shortest_strand method. But I realized that is a bad idea. In addition, iterating to the end of string1 and also ensuring that we were comparing to an existing base pair in string2.