March 20 (Reuters) - U.S. gene-testing company Affymetrix Inc's board on Sunday rejected a $1.5 billion bid by Origin Technologies Corp, saying it stood by a $1.3 billion merger deal with Thermo Fisher Scientific Inc.

Origin, made up of a group of former Affymetrix executives, made the offer on Friday, looking to derail the deal with Thermo Fisher.

Thermo Fisher, the world's largest maker of scientific instruments, agreed in January to buy Affymetrix for $1.3 billion in cash.

In reviewing the Origin proposal, the Affymetrix board said Origin appeared to be a newly formed shell entity with no assets of which Affymetrix was aware, and whose sole source of funding for the proposed transaction was $1.5 billion in potential debt commitments.

"We held preliminary discussions in the fall of 2015 with individuals who became principals and potential backers of Origin, and in November 2015 I invited them to submit a written proposal if they had serious interest in a strategic transaction with Affymetrix," Dr. Frank Witney, Affymetrix's chief executive officer, said in a statement.

"We heard nothing further from them for over four months until they announced their unsolicited proposal on March 18," Witney said.

Based on the analysis performed by its advisers, Affymetrix said Origin's funds fall "materially short of the funds that would be required to complete the transaction, including a termination fee payable to Thermo Fisher."

In a separate news release, Thermo Fisher said it continued to believe its agreement to merge with Affymetrix remained in the best interests of both Affymetrix and its stockholders.

Officials at Origin were not immediately available for comment.

(Reporting by Scott DiSavino in New York; Editing by Peter Cooney)