Answer:
1/3
Explanation:
Let's assume that the allele "P" imparts purple phenotype to flowers while the allele "p" gives white phenotype. The self-fertilization of purple-flowered parent plants gave purple and white progeny in almost 3:1 (28:10) ratio. This means that the parent plants were heterozygous and the genotype of each was "Pp".
A cross between Pp and Pp produces progeny in the following genotype ratio=
1/4 PP: 1/2 Pp: 1/2 pp
So, out of total 3/4 purple progeny, 1/3 is homozygous for the purple allele (PP) while the rest 2/3 is heterozygous dominant.
