Some gametes are also known as OVA, which is a three-letter word. OVA are reproductive cells that are produced by female organisms and are the counterpart to sperm cells, which are produced by male organisms. OVA are haploid cells that contain half the genetic material of the organism, while sperm cells contain the other half. When an ovum and a sperm cell combine, they form a zygote, which is the first stage of a new organism.