Self-crossing Mendel's yellow-seeded F2 plants showed that the fraction breeding true was:

1. Yellow F2 plants are a mixture of two different genotypes. 2. When he self-crossed the F2 plants expressing yellow seeds, he found that one-third of the plants bred true. 3. The other two-thirds segregated at a 3 to 1 ratio of yellow to green seeds. 4. The true-breeding plants had homozygous YY genotypes. 5. The segregating plants corresponded to the heterozygous Yy genotype. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 12 'Mendel's Experiments and Heredity', sections 12.1-12.3_