Heterozygous

Sow Carolina Gold rice and you'll generally grow Carolina Gold, the same as the parent. You can save some for seed if you like.

Sow seeds from a Honeycrisp apple and, with a little sun and rain, you'll grow apple trees, but not Honeycrisps.

Unlike rice, apples do not breed true; apple varieties must be propagated by grafting scionwood onto rootstock.

Apples are heterozygous, indeed are "extreme" heterozygotes. Their genetic makeup includes variations, or alleles, that combine randomly and cause significant differences from each apple's parents.

Even the same apple parents can produce very unlike offspring—like another heterozygous species, humans.

Rice, compared to apples, is homozygous. If you could breed apples for self-fertility and homozygosity (can you?), it would still be hard to keep your trees from being fertilized by other varieties.

Johnny Heterozygoteseed public-domain image

Apples from seed are called pippins and each seed grows different fruit. A pippin becomes a cultivar—a cultivated variety—if grafted. Most pippins do not make the cut; human taste is the natural selector.

John Chapman (Johnny Appleseed) sowed pippins (and plant diversity), but modern farmers graft, or plant grafts.

Consequently the original pippin tree of every grafted cultivar is, in a real sense, alive and well on multiple rootstocks. The McIntosh apple you ate last fall grew on a limb of the same tree that John McIntosh discovered on his Ontario farm in 1811.

More meditations on apple genetics from Chris at A Life of Apples.