If the frequency of one of the alleles is close to zero when the simulation starts, if there is no selection, is it likely to persist?

NO, if the frequency is low the alleles is not persisting according to the rule of natural selection.

Explanation:

Directional selection leads to increase over time in the frequency of a favored allele. Among alleles dominance relationship advantageous rate gets fixed. The reason behind it is rare alleles are mostly found in heterozygotes.

By natural selection when it reaches high frequency then recessive mutation can be seen. After reaching on advantageous allele reached at high frequency that time deleterious alleles are very necessarily rare and due to this it is mostly present in heterozygotes

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.