The proportion of one particular type of allele to the total of all alleles at this genetic locus in a breeding population is known as gene frequency or allele frequency.
The proportion of frequency of any particular genotype among the inviduals of a population is known as genotype frequency.
If any population of 200 individuals consists of 20 BB, 40 Bb and 140 bb individuals.
Genotypic frequencies of BB or f (BB) is 20/200= 0.1
Genotypic frequency of Bb or f (Bb) is 40/200= 0.2
Genotypic frequency of bb or f(bb) is 140/200= 0.7
The frequecny of B gene or f (B) will be 0.1 (from BB) + 0.1 (from Bb) = 0.2.
The generalized expression of allele B is f (B)= f (BB) + 1/2 f (Bb).