Final answer:
When a single sperm cell unites with an ovum in the Fallopian tube, fertilization occurs, forming a zygote. This zygote then undergoes several stages of development before implanting in the uterus.
Step-by-step explanation:
Typically, when a single sperm cell unites with an ovum in the Fallopian tube, fertilization takes place. This remarkable process involves a haploid sperm cell entering a haploid egg, leading to the formation of a diploid cell known as a zygote. The zygote contains genetic information from both parents and is thus equipped with the complete genetic blueprint for a new human being. The fertilized egg, now a zygote, will then go through several stages, including cleavage, which is the initial phase of mitotic cell divisions. Following this, the zygote transforms into a morula and then into a blastocyst during the process of blastulation.
Remarkably, fertilization is a selective process. Among the hundreds of millions of sperm released during ejaculation, only one succeeds in penetrating the egg's outer layers, the corona radiata and zona pellucida, to ultimately fuse with the egg's plasma membrane. After fertilization, the zygote undergoes rapid development while remaining in the fallopian tube for approximately 72 hours before continuing its journey to the uterus for implantation.