Define/Explain the following terms:
$1.$ Mutation
$2.$ Alleles

(N/A) Mutation: $A$ sudden heritable change in the $DNA$ sequence,which results in changes in the genotype and phenotype of an organism. It can be caused by changes in base pairs or alterations in chromosome structure or number.
Alleles: These are slightly different forms of the same gene. They occupy the same locus on homologous chromosomes and control the same trait,but may produce different phenotypic expressions.