Two developmental biologists have accepted joint tenure offers from the Departments of Cellular and Developmental Biology and of Biochemistry and Molecular Biology, University officials said yesterday.

Elizabeth Robertson, associate professor of genetics and development at Columbia Medical School, and Andrew McMahon, an associate member of the Roche Institute of Microbiology in Nutley, New Jersey, will hold the first-ever joint appointments between the two departments.

The date for the two scientists' arrival has not been finalized.

Faculty members said they hope the posts will help to increase interaction between two departments. Officials said that both Robertson and McMahon will probably teach courses in mammalian development, as well as in other areas of modern molecular development.

Both biologists have studied genetic mutations and their role in development. McMahon researches the wnt gene, which is potentially important in signaling crucial events in the embryonic development of the central nervous system and brain.

Robertson's work focuses on early embryogenesis, using gene targeting experiments. In these experiments, embryonic "stem cells" are injected into new host embryos to test their effects on embryonic development.

Faculty members praised Robertson and McMahon yesterday, citing the new fields of knowledge which they would add to both departments.

"I'm delighted," said Professor of Biochemistry and Molecular Biology Douglas A. Melton. "I think both of them bring to the Harvard campus expertise in teaching and research in mammalian development and genetics."

Melton said that the appointments would strengthen the study of mice and of vertebrate development in both departments, which he said are already strong in research of simple of organisms.

Biochemistry Department Chair Stephen C. Harrison '63 said that Robertson and McMahon, who are both in their mid-30's, would generate excitement in both departments.

"Both are outstanding young investigators," said Harrison. "I think that together with Professor Melton, we will now have an extraordinary group of experimenters in developmental biology."

Harrison said that the professors' presencewould mean richer course offerings and researchopportunities for undergraduates, and wouldattract top graduate students as well.

"It will make Harvard a center of what is seenas a major thrust in current biological concerns,"he said.

A `First-Rate' Teacher

Harrison said that although McMahon is notcoming to Harvard from a university post, he isconfident the biologist will make a "first rate"teacher. He said McMahon has taught classes atCold Spring Harbor Biological Laboratories in NewYork and at the Marine Biology Laboratory in WoodsHole, Mass.

Columbia Medical School professor of geneticsand development Frank Costantini, who has workedwith Robertson on several projects, said that thedepartment there would be sorry to see her go.