ABO blood groups in humans are controlled by the gene I. There are six different genotype and four different phenotype in human population. What is the ratio of allele in sperm and population ?

The correct option is B 1 : 3
In one single sperm there will be single allele coming from the father which will contribute and determine the offspring's blood group. It could be any one from IA, IB and i. Thus, if there is 1 allele in a sperm and three in total population, therefore the ratio will be 1:3.

So, the correct option is '1:3'.