Main event: fertilization.
This is the week when pregnancy really begins.
The sperm and egg meet and fuse together in one of the fallopian tubes. The fertilized egg is called a "zygote". If more than one egg is fertilized, the pregnancy will be multiple (two children or more).
A normal zygote consists of 46 chromosomes: 23 chromosomes from you and 23 from your father. Chromosomes determine the sex of the unborn child, which depends on the sex chromosome of the father: if the sperm carries a Y chromosome, a boy will be born, if the X chromosome carries a girl.
Chromosomes also determine such characteristic features as eye and hair color, hereditary psychotype, behavioral characteristics and, in a sense, the personality of the child.
24 hours after fertilization of the egg, the zygote begins to divide into two cells. Over the next 72 hours, cell division continues, resulting in a small group of cells that resembles a raspberry in appearance and is called a “morula.” During its internal fragmentation into new cells, the morula moves along the fallopian tube towards the uterus.