Twо pure-breeding tоmаtо lines differing greаtly in fruit mаss were crossed, and the F₁ was self-fertilised. Several hundred F₂ plants were grown together under uniform conditions, genotyped at many marker loci, and weighed. Results for three marker loci are summarised below. M and m denote the marker alleles inherited from the large-fruited and small-fruited parent respectively. Marker locus Mean mass, MM (g) Mean mass, Mm (g) Mean mass, mm (g) Locus D 92 71 48 Locus H 70 72 69 Locus K 78 71 64