Can you feel fear without the frontal lobe?

No

-What part of the brain is responsible for feeling fear?

The fear response starts in a region of the brain called the amygdala. This almond-shaped set of nuclei in the temporal lobe of the brain is dedicated to detecting the emotional salience of the stimuli – how much something stands out to us.

-How does the brain react to fear?

As soon as you recognize fear, your amygdala (small organ in the middle of your brain) goes to work. It alerts your nervous system, which sets your body's fear response into motion. Stress hormones like cortisol and adrenaline are released. Your blood pressure and heart rate increase.

-What is the root of fear?

Even so, our brains are hardwired for fear — it helps us identify and avoid threats to our safety. The key node in our fear wiring is the amygdala, a paired, almond-shaped structure deep within the brain involved in emotion and memory

all the above is what i would say