ABSTRACT
Targeting or tagging of a gene underlying a particular trait of interest serves two purposes. The fi rst is that such a tagged gene can be cloned and its function revealed through its role in the phenotype. This is map-based cloning when it is initiated from tightly linked markers. Gene cloning helps us understand how a particular trait is infl uenced by genes and how these genes contribute to the development of the trait. The cloned gene can be
Department of Renewable Resources, University of Louisiana at Lafayette, Lafayette, LA, USA; e-mail: yxw9887@louisiana.edu
introduced into other plants if trait transfer is so desired through either direct gene transfer or molecular breeding. For example, the gene that determines andromonoecy (a) in melon has been cloned (Boualem et al. 2008). Sex determination in melon is determined by the interplay of a and gynoecious (g). Monoecious and andromonoecious plants have genotypes of A_G_ and aaG_, respectively while AAgg is gynoecious and aagg is hermaphrodite (Poole and Grimball 1939; Keningsbuch and Cohen 1990). External factors, such as ethylene, can modify sex expression. Actually, the cloned a gene encodes for a 1-aminocyclopropane-1-carboxylic acid sythase (CmACS-7). The enzyme catalyzes the fi rst committed and rate-limiting step in ethylene biosynthesis in plants. The gene is specifi cally expressed in the carpel primordia of female and hermaphrodite but not male fl owers during early stages of fl ower development. This leads to ethylene production, which affects the development of the stamina in female fl owers but is not required for carpel development (Boualem et al. 2008).
