What happens to a zygote after it forms and begins to develop

In humans, it takes about four days for a zygote to become a  morula  and another three days until the embryo attaches itself to the mother's uterine wall.

c) 50% there are four chromosomes. after crossing over, 2 of the four have been changed. that means any gamete has a 2 in 4 chance or 50% chance of receiving the mutated chromosome.