Why is mutation needed for evolution to occur even though it usually has little effect on allele frequencies

Debra has to give medicine to look at every morning for the next 14 days how many weeks is this

Many farmers prefer cattle without horns because it is safer for their herds. the allele for no horns (n) is dominant to the allele for the presence of horns (n). a farmer mates a male with horns to a heterozygous female without horns. what is the chance that the offspring will have horns?

What is the compliment dna strand to the following sequence: ttgactaggcta