Scientists make cells that form eggs and sperm in lab

The findings could lead to new understanding of inherited diseases and transform treatments for infertility, they said.

"We are really trying to look at the origins of normal and abnormal human development by going to the source," said Dr. Renee Riejo Pera of Stanford University in California, whose study appears in the journal Nature.

"For years and years, we haven't had the ability to look at how germ cells -- the cells that give rise to eggs and sperm -- how they are made -- what genes are required, what pathways are active," Pera said in a telephone interview.

This part of the human reproductive cycle cannot be studied in animals because the genes involved are unique to humans.