A high-frequency recombination cell (Hfr cell) (also called an Hfr strain) is a bacterium with a conjugative plasmid (often the F-factor) integrated into its genomic DNA. The Hfr strain was first characterized by Luca Cavalli-Sforza. Unlike a normal F⁺ cell, hfr strains will, upon conjugation with a F⁻ cell, attempt to transfer their entire DNA through the mating bridge, not to be confused with the pilus. This occurs because the F factor has integrated itself via an insertion point in the bacterial chromosome. Due to the F factor's inherent nature to transfer itself during conjugation, the rest of the bacterial genome is dragged along with it, thus making such cells very useful and interesting in terms of studying gene linkage and recombination. Because the genome's rate of transfer through the mating bridge is constant, molecular biologists and geneticists can use Hfr strain of bacteria (often E. coli) to study genetic linkage and map the chromosome. The procedure commonly used for this is called interrupted mating.

Lionel Andrés Messi (Spanish pronunciation: [ljoˈnel anˈdɾes ˈmesi], born 24 June 1987) is an Argentine footballer who plays in La Liga for FC Barcelona and is the captain of the Argentina national team, mainly as a forward.

By the age of 21, Messi had received Ballon d'Or and FIFA World Player of the Year nominations. The following year in 2009 he won both the Ballon d'Or and FIFA World Player of the Year, and won the inaugural FIFA Ballon d'Or in 2010 and 2011. He also won the 2010–11 UEFA Best Player in Europe Award. Messi is the fourth football player to win three Ballons d'Or, after Johan Cruyff, Michel Platini and Marco van Basten and the second player to win three consecutive Ballons d'Or, after Michel Platini. His playing style and small stature have drawn comparisons to Diego Maradona, who himself declared Messi as his "successor".

Messi has won five La Liga titles and three Champions League titles. In 2012, Messi made UEFA Champions League history by becoming the first player to score five goals in one match, in a 7–1 win against Bayer Leverkusen. With two goals in the next round against A.C. Milan, he matched José Altafini's record of 14 goals in a single UEFA Champions League/European Cup season. He also became the first player to top-score in four successive European Champion Clubs' Cup campaigns. He set the world record for most goals scored in a season during the 2011–12 season, with 73 goals.