Mitochondria are thought to be the descendants of certain alpha-proteobacteria. They are, however, no longer able to lead independent lives because most genes originally present on their chromosome have moved to the nuclear genome. Which phenomenon accounts for the movement of these genes?
a. plasmolysis
b. conjugation
c. translation
d. endocytosis
e. horizontal gene transfer

E) horizontal gene transfer

Explanation:

Horizontal gene transfer(HGT) is mainly seen in bacteria. Bacteria exchange their genetic material from the horizontal gene transfer method. There are three methods in HGT- conjugation, transduction, and transformation.

In conjugation, the bacteria exchange their plasmid through sex pilus. In transformation, bacteria take up other's genetic material from its environment and in transduction virus-mediated gene transfer occurs.  

Therefore in bacteria and nucleus, the genetic material exchange can occur only through HGT.