When the sperm enters the egg, cells start the process, mitosis and meiosis, of replicating. Those cells, however few they are, have their own DNA. They are a separate organism.
That is when life begins. This is not opinion. It is biology. The above is true regardless whether we’re talking about chickens, dogs, or humans.
Exactly.
And look at this: 
Notice that the fertilized egg grows from a single cell to a blastocyst of about 100 cells before it ever implants into the uterine wall. It is living and growing all on its own without the mother's help before it attaches.
They want to make it seem like the baby is a parasitic entity that relies completely on the mother from the moment of conception. Not so.
One other thing as well. A mother’s immune system’s only job is to be able to tell what IS part of her body from what ISN’T part of her body.
During pregnancy, the fetus needs to be shielded from the mother’s immune system. If that doesn’t happen, the immune system attacks it and kills it.
Why? Because it doesn’t recognize the fetus as part of the body.
The immune system makes a liar out of every pro-choicer. She may say “its my body” with her mouth, and believe it in her head, but her own body contradicts her every second of every day.