It is formed through a mechanism known as crossing over and recombination.
A human embryo forms by fertilization of sperm (male gamete) and ovum (female gamete).
Each of these gametes has half the number of chromosomes than present in human embryo/infant/child/adult.
In fertilized one cell zygote (first stage of embryo) chromosomes from sperm and ovum are paired and then undergo division.
Paired chromosomes in zygote undergo crossing over and recombination exchanging genetic material or DNA.
The zygote undergoes further cell divisions and differentiation to develop into an embryo, fetus and new born baby.
This baby has combined genetic material from both parents arranged in a new and unique form of DNA sequence.
Hope this helps.