Let's start wayyyy back before you were even around
In the NUCLEUS of a random cell in mommy's body
(this is the nucleus)
(this is what DNA looks like. It's in the shape of a double helix)
And inside that nucleus is a sting of proteins called DEOXYRIBOSE NUCLEIC ACID or DNA for short.
DNA is very very important, because its the order of the proteins on it that tell our body what to look like and how to act.
The parts that we care about the most are the little proteins in between the sugar phosphates, Adenine, Thymine, Cytosine and Guanine, in the pattern, A-T and C-G
But DNA in its normal form can't leave the nuclues. It has to change itself into RNA, to leave and relay messages to the site of protein synthesis in the cytoplasm.
All of our genetic information is copied onto RNA from DNA during a process called Transcription. The mRNA then takes this out of the nucleus and is then, through the process of translation, which assemble into amino acids which form polypeptides.
Transcription begins with the enzyme RNA polymarise, which copies the DNA strand down stream of the TATA box which signals the start of what needs to be copied, and turns it into mRNA. Eventually the RNA polymarise meets the termination signal which tells it to stop going.
Then translation starts. The mRNA goes to a ribosome, where it is accepted into the organelle. Ribosomes are made of a mix of proteins and rRNA, which provide binding sites for the incoming mRNA to mesh with tRNA. The mRNA enters the ribosome and as it goes through it is read three letters at a time, a set of three is called a codon, the ribosome then finds the matching sequence of tRNA and anti-codon to create the appropriate amino acid. As the mRNA moves through the amino acids link forming a polypeptide chain.
...And that's how Mommy got the biological need to have children with your father.