Final answer:
A germline mutation that can be passed down generations occurs before meiosis, and is hereditary because it is present in the gametes that combine during fertilization, affecting the whole organism and can be transmitted to offspring.
Step-by-step explanation:
A germline mutation occurs prior to meiosis and is significant for inheritance as it can be transmitted from generation to generation. This is because germline cells, such as egg and sperm, combine during fertilization forming a zygote with a unique combination of DNA, including any mutations. Contrary to somatic mutations, which affect non-reproductive cells and cannot be hereditary, a mutation in germline cells can lead to widespread implications across the entire organism’s body and can be passed down to offspring.
As for the event that leads to a diploid cell in a life cycle, the correct answer is meiosis. The complete cycle of passing genetic information includes the cell cycle and mitosis or meiosis followed by fertilization. Both processes are essential to ensure the continuation of species through sexual reproduction, providing variation in the gene pool, which is essential for evolution.