In what could be the first step towards same-sex couples having their own genetic children, reproductive scientists have produced male and female mice from two fathers using stem cell technology. The achievement of two-father offspring in a species of mammal could also be a step toward preserving endangered species, improving livestock breeds, and advancing human assisted reproductive technology (ART).

A team of reproductive scientists in Texas, led by Dr. Richard R. Berhringer at the University of Texas M.D. Anderson Cancer Center, manipulated fibroblasts - a type of cell that are the most common cells of connective tissue in animals - from a male (XY) mouse fetus to produce an induced pluripotent stem (iPS) cell line. About one percent of iPS cell colonies grown from this XY cell line spontaneously lost the Y chromosome, resulting in XO cells.

These XO iPS cells were injected into blastocysts from donor female mice before being transplanted into surrogate mothers, which gave birth to female XO/XX chimeras having one X chromosome from the original male mouse fibroblast.

The female chimeras, carrying oocytes - which are immature ovum or egg cells - derived from the XO cells, were mated with normal male mice. Some of the offspring were male and female mice that had genetic contributions from two fathers.

The technique, which is described in a study posted on Wednesday at the online site of the journal Biology of Reproduction, could be applied to livestock breeding to combine desirable genetic traits from two males without having to outcross to females with diverse traits.

The scientists also point out that this "new form of mammalian reproduction" could also be valuable for preserving species when no females remain as it would be possible for one male to produce both oocytes and sperm for self-fertilization to generate male and female progeny.

They add that, in the future, it may also be possible to generate human oocytes from male iPS cell in vitro. Used in conjunction with in vitro fertilization, this would eliminate the need for female XO/XX chimeras, although a surrogate mother would still be needed to carry the two-father pregnancy to term.

Additionally, using a variation of the iPS technique, the researchers say, "it may be possible to generate sperm from a female donor and produce viable male and female progeny with two mothers."

However, the authors caution that the generation of human iPS cells still requires significant refinements prior to their use for therapeutic purposes, so there's still some time to explore the moral and ethical questions such technology will no doubt raise.