Somatic mutations are best described by the option b) not transmitted to progeny. This is because somatic mutations occur in non-germline cells, meaning they do not affect the reproductive cells (sperm and eggs) and therefore are not passed on to the next generation.
When a mutation occurs in a somatic cell, it can lead to cell changes and potentially contribute to conditions such as cancer, but it will remain within the individual organism and will not be inherited by offspring. This distinguishes somatic mutations from germline mutations, which occur in the germ cells and can be inherited. Therefore, the correct choice regarding somatic mutations is that they are not transmitted to progeny.