My mom had rectal cancer, what are my chances of getting it to?

Among all the cases of colorectal cancers (cancers of the colon or the rectum), only about 30% of them are familial (i.e. run in the family). Of those, 10% are part of the so-called FAP cancers, i.e. cancers derived from a syndrome called Familial Adenoma Polyposis (caused by the germinal mutation of the APC gene), and could be easily diagnosed by the presence of polips in the large intestine mucosa. Another 20% are the so-called HNPCC cancers (hereditary non-polyposis colon cancer), but the incidence of colon cancer in family with these syndrome is very high (about 85%), therefore easily spotted, too. These tumors are given by the mutations of a family of genes called MMR genes (hMLH1, hMSH2 and hMSH6). If your mum is the only relative with an history of colorectal cancer, her tumor is most likely to be "sporadic", i.e. non-hereditary, therefore you would not have a chance higher than anybody else to getting it, too. If you are very worried, there are tests available for the early detections of mutations on the genes I mentioned earlier, which you could undertake.

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Best of luck to you and your mum!

It depends. If that type of cancer runs in your family, than the chances are, you might get it also, however, if it doesnt run in your family, the chances are that you will not. And cancer does not spread form person to person if that's what you're asking.

You are at greater risk but not sure how much greater risk. So long as your doc knows about your family history of colo-rectal cancer they will begin screening you earlier than usual for it. If you notice any change in your bowel habits or rectal bleeding be sure to let your doc know about it.