Gene targeting is one strategy to determine the function of a gene. Basically, a scientist can experimentally modify a gene in an organism and then look at its effect on phenotype. For example, if DNA encoding one allele of a gene is added to moss cells, it can replace the allele carried by the moss. When the altered cells then grow into protonema, they will express the new allele and the moss will have an altered phenotype. What unique feature of moss allows it to be useful for gene targeting