The unicellular green alga Chlamydomonas has a single large chloroplast containing many copies of a circular double-stranded DNA.

Its strR (streptomycin resistance) trait exhibits uniparental inheritance: the phenotype is transmitted only through the mt+ (mating type) parent.

Reciprocal crosses yield offspring which only express the genotype of the mt+ parent.

After fertilization, the single chloroplasts of the two mating types fuse.

The resulting chloroplast only retains DNA from the mt+ parent.