The present invention relates to methods for constructing a recombinant fungal host cell comprising one or more copies of a polynucleotide construct integrated in its genome, said method comprising transforming a fungal host cell with an integrative polynucleotide construct comprising a first polynucleotide encoding a selectable marker, wherein the first polynucleotide, a 5′ untranslated region thereof and/or a riboswitch operably linked therewith comprises a spliceosomal intron which has 5 nucleotides or less between its branch site and its acceptor site; and a second polynucleotide encoding a polypeptide of interest; as well as suitable polynucleotide constructs, resulting fungal host cells and methods of manufacture.