Answer: The correct answer for the blanks are-
mitochondrion / chloroplast.
Step-by-step explanation:
Endosymbiosis is an evolutionary theory that describes the origin of two eukaryotic organelles that are mitochondria and chloroplasts, which possess bacterial like characteristics. According to this theory, over millions of year back, prokaryotes were thought to live inside larger cells (as symbionts) and later they became the part of it.
This describes the origin of chloroplast and mitochondria that possess their own genetic material.
Thus, first option is the right answer.