A method for obtaining improved fertility restorer lines for male sterile crop plants and a DNA construct for use in said method are disclosed. The invention relates to the simultaneous use of two different gene sequences encoding the same protein product, one being the naturally occurring wild type sequence and the other sequence being generated by modification of the wild type sequence for expression in crop plants by using codon degeneracy to avoid homology between the two sequences at the DNA and mRNA levels, each of the said sequences being placed under independent transcriptional control of different overlapping plant tissue-specific regulatory elements in the same DNA construct.