Calculate the frequency of the recessive allele in the population?

Butterflies with solid wings must have two recessive alleles since that is the recessive trait. Since ten of them are solid, there must be 20 recessive alleles since each butterfly has two alleles. Since your problem has no heterozygous organisms, the rest must be homozygous dominant, but that doesn't matter to solve the problem. To find the percentage/frequency of the recessive allele, divide the number of recessive alleles by the total number of alleles. Since there are 25 butterflies left, each with 2 alleles for wing type, there are a total of 50 alleles. 20/50=40%.