Final answer:
The Egyptian mortuary custom related to both Jacob and Joseph is mummification, which was essential in Egyptian beliefs connected to the afterlife and involved embalming and preserving the body.
Step-by-step explanation:
The Egyptian mortuary custom mentioned in connection with both Jacob and Joseph is mummification. This process was integral to the Egyptian belief in the afterlife, where preserving the body after death through mummification was crucial for one's soul to live on. Detailed descriptions of the mummification process can be seen in the numerous artifacts and tombs discovered which include mummified bodies, canopic jars for storing removed organs, funeral statuettes such as shabti, and elaborate burial tombs designed to guide and protect the deceased in the afterlife.
In the biblical narrative, when Jacob died in Egypt, Joseph ordered that his father's body be embalmed, adhering to the Egyptian mortuary practices. Similarly, upon his own death, Joseph's body was also embalmed and later carried out of Egypt during the Exodus. These instances illustrate a profound cultural exchange and integration of traditions between the Egyptians and the Hebrews during their time in ancient Egypt.