NEW YORK — Two well-known companies surged in their market debuts Thursday despite what has recently been a difficult market for initial public offerings.

Shares of Hyatt Hotels Corp. jumped 12 percent in their first day on the New York Stock Exchange as markets appeared to dismiss concerns about infighting among its founder's heirs and tepid hotel reservations around the world.

Meanwhile, investors impressed by Ancestry.com's large subscriber base and growth story pushed the genealogy Web site's stock up as much as 21 percent on the Nasdaq market.

"I have to say, it's a very dangerous market right now, especially considering how many deals have recently missed their target or withdrawn," said David Menlow, president of IPOfinancial.com. "It's easy to connect those dots and assume the entire IPO market has heavily stalled. But that was obviously not the case today."

Five of the last nine IPOs have closed below their offering price in the first day, while others have suspended plans to go public. Texas bank PlainsCapital Corp. blamed market swings when it postponed its IPO late Wednesday. Energy company AEI and Aviv REIT Inc., a real estate investment trust that focuses on health-care properties, have also called off deals in the past week.

Ancestry priced 7.4 million shares at $13.50 each late Wednesday — the midpoint of its expected range of $12.50 to $14.50 — to raise $100 million in its initial public offering. The stock rose 70 cents, or 5.2 percent, to close at $14.20 Thursday. It earlier traded as high as $16.32 and as low as $14.06.

Underwriters are being offered up to an additional 1.1 million shares to cover overallotments, which would boost total proceeds to nearly $115 million. The stock trades on the Nasdaq market under the ticker symbol "ACOM."

The company, based in Provo, Utah, has more than 1 million paying subscribers and plans to use net proceeds of about $48.4 million for general corporate purposes and to repay debt. It said it may also use a portion to expand through acquisitions or investments in technologies.

Menlow said he sees Hyatt's successful debut as a "mini-turning point," but not necessarily an indication that the entire market is rebounding.

"These two deals aren't the litmus test for the health of the IPO market, but it certainly does add strength to the argument that the market has been under the siege of some sort of psychological uncertainty," Menlow said. "With the right deals, markets are willing to step up and take positions."

Shares in Hyatt, which is based in Chicago, priced late Wednesday at $25 a piece, near the top end of the $23-to-$26 range, raising $950 million. The iconic hotel chain's shares stayed above that price Thursday, trading between $25.75 and $28.26. The stock closed $3 higher, or 12 percent, at $28.