Which of the following is true about germline mutations?

Germline mutations are alterations in the DNA that occur in the germ cells, which are the reproductive cells of an organism. These mutations can be passed on to the next generation when these germ cells participate in reproduction, leading to the inheritance of the mutation in the offspring. This is a fundamental principle of genetics, as offspring inherit a combination of genetic material from both parents, including any mutations that may have originated in their germline cells.

In contrast, mutations that occur in somatic cells, which are all the cells in the body except for the germ cells, do not get passed on to the next generation. Therefore, the ability of germline mutations to be inherited distinguishes them from other types of mutations.

The other options do not accurately describe germline mutations. While germline mutations can influence an organism's phenotype, they are not limited to environmental causes; they can also occur spontaneously during DNA replication or due to inherent genetic factors. Hence, the statement that germline mutations can be inherited by the next generation is the most accurate representation of their significance in genetics.