Answer: Zygote
Step-by-step explanation:
A zygote, also called a fertilized egg, is the phase of conception where the egg and sperm join to form a single cell. The zygote contains a full set of chromosomes, with 23 from the egg and 23 from the sperm. The zygote phase lasts only about four days, after which the single cell splits rapidly to become a blastocyst and then an embryo.