Flower color in sweet pea in part comes from the pigment anthocyanin. One step is catalyzed by an enzyme called chalcone synthase. When chalcone synthase doesn't work at all , the flowers are white. The normal enzyme is denoted + whereas the non-functioning enzyme is denoted -. Heterozygotes are purple. In a particular large population the following genotype frequencies are observed:
genotype frequencies
Genotype Frequency
++ 0.60
+- 0.20
-- 0.20
What is the frequency of the - allele in this population?

0.30

Explanation:

Chalcone synthase is an enzyme ubiquitous to higher plants and belong to the family of polyketide synthase enzyme known as type lll PKS. Type lll PKS are associated with the production of chalcones, a class of organic compounds found manly in plants as natural defense mechanisms and as synthetic intermediates CHS was the first type lll PKS to be discovered. it is the first committed enzyme in flavenoid biosynthesis. the enzyme catalyze  the conversion of malonyl-coA to narigenin chalcone.

the denominator has a very specific role.