UPDATE 1-Ancestry.com shares jump in debut

* Shares up 10.5 pct in debut

* Backed by Spectrum Equity (Updates with details about share move)

NEW YORK, Nov 5 (Reuters) - Ancestry.com Inc (ACOM.O), a website backed by Spectrum Equity Investors, rose in its initial public offering debut on Thursday.

The company priced the 7.4 million shares at $13.50 per share on Wednesday, within an expected range.

Ancestry.com, which operates a website that allows people to trace their family roots by scouring online records.

The Provo, Utah-based company had expected to sell 7.4 million shares in its IPO for between $12.50 and $14.50 each, in a $100 million offering.

Its shares were up 10.5 percent to $14.92 in early afternoon trading on Nasdaq.

Ancestry.com, which said it had 1 million subscribers as of September, was founded in 1983 and is majority owned by private equity firm Spectrum, whose stake in the company will fall to 54.8 percent after the IPO from 67 percent. Spectrum bought Ancestry.com for $354.8 million in December 2007.

Existing shareholders are selling about 45 percent of the shares in the IPO, with the rest coming from the company.