Assertion $(A)$: Mutation results in changes in genotype and phenotype of an organism.
Reason $(R)$: Mutation leads to alteration of $\text{DNA}$ sequences,i.e.,variations in $\text{DNA}$.
Choose the correct answer from the options given below.

• A
  Both $(A)$ and $(R)$ are correct and $(R)$ is the correct explanation of $(A)$.
• B
  Both $(A)$ and $(R)$ are correct but $(R)$ is not the correct explanation of $(A)$.
• C
  $(A)$ is correct but $(R)$ is not correct.
• D
  $(A)$ is not correct but $(R)$ is correct.