Final answer:
An F positive (F+) recipient cannot form a connection with an F positive (F+) donor because once a cell becomes F+, it no longer initiates pilus formation or DNA transfer to another F+ cell, as the purpose of conjugation is to transfer the F plasmid to F- cells.
Step-by-step explanation:
An F positive (F+) recipient would not be able to form a connection with an F positive (F+) donor due to the mechanism through which the F plasmid is transferred. The F plasmid contains genes that enable a bacterial cell to form a pilus, a direct connection used for conjugation with an F negative (F-) recipient cell. Once the recipient cell receives the F plasmid and expresses its genes, it becomes an F+ cell itself. Because both cells are F+, neither will attempt to form a pilus and transfer genetic material to the other since the pilus is typically extended by an F+ cell to transfer the plasmid to an F- cell (recipient).
In essence, the presence of the F plasmid in both cells negates the initiation of the transfer process, as the main function of the F pilus and associated mechanisms is to propagate the F plasmid across a population where some cells do not yet possess it. Hence, the sex pilus formation and subsequent conjugation are prevented when both participating cells are F+.