In which part of human genetics do mutations originate?

Mutations originate in the genotype, which refers to the genetic constitution of an individual. The genotype encompasses all the hereditary information encoded in the DNA, including genes and the variations or alterations within those genes, known as mutations. These alterations can occur due to various factors such as environmental influences, errors during DNA replication, or exposure to certain chemicals.

When mutations happen in the genotype, they can lead to changes in the phenotype, which is the observable characteristics or traits of an organism. However, it is the genotype where the mutations fundamentally occur, thus directly linking the source of genetic variation to the genotype itself. Other choices refer to different aspects: the protein pertains to the expression of genes, mitochondria is related to cellular energy production and not directly to genetic mutations, and phenotype relates to the manifestation of genetic traits rather than their origin.