The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
A germline mutation is any detectable and heritable variation in the lineage of germ cells. Mutations in these cells are transmitted to offspring, while, on the other hand, those in somatic cells are not. Nonlethal mutations accumulate within the gene pool and increase the amount of genetic variation. The abundance of some genetic changes within the gene pool can be reduced by natural selection, while other "more favorable" mutations may accumulate and result in adaptive changes. So, mutations occurring in the germinal cells of the gonads are called germ mutations. They are heritable raw materials for natural selection lead to origin of new species. So, both Assertion and Reason are correct and Reason is the correct explanation for Assertion.