Rna primers must be present on which strand during dna synthesis?

Both on the leading strand and on each okazaki fragments of the lagging strand.

Explanation:

A primer is a short single-stranded RNA nucleotide that initiate DNA synthesis at the replication fork. Because DNA polymerase can not initiate replication on it own short strand of RNA primer synthesized by an enzyme RNA primase is needed to initiate DNA polynucleotide synthesis.

RNA primer is present on both leading and lagging strand.

RNA primer of about 10 nucleotides long are present on the leading strand and on each okazaki fragments on the lagging strand to initiate replication. The RNA primer is removed and replaced by DNA nucleotides by DNA polymerase.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).