Is rectal cancer hereditary?

Usually not . Most patients with rectal cancer have not inherited it. A small subset have genetic mutations that put them at risk. Probably around 5 % of rectal cancers are hereditary. .
It can be. Cancer is where a cell literally becomes immortal and does not die but can still replicate itself. Genetic mutations cause this. Most genetic mutations that cause cancerous cells happen after we are born, but rarely we can inherit a bad gene. Construct a medical family tree and if colon or rectal cancer affects 2 or more across 2 generations and 1 is less than 50 must talk with doctor.
It can be. 30% of colorectal cancers are hereditary. This means if you have a first degree (mother, father, brother, sister) relative with rectal cancer, you are at risk and should be screened earlier. If it is a more distant relative, it is harder to say what your risk is. Certainly, if you are symptomatic, it should be worked up.
Yes. Having a first degree family member with colon or rectal cancer increases your likelihood of colon cancer too. This is even more pronounced if that person had cancer before the age of 60. Colon cancer screening is recommended starting at age 40 for people with a first degree family member with colon cancer or 10 years earlier than they were diagnoses, whichever comes first.