Having a so-called non-traditional family just got easier – if you’re a mouse. Well, actually it’s still not easy, as you’ll see if you keep reading, but at least it’s doable. Researchers yesterday reported using stem cell technology to create mice with two dads, and no mums, genetically speaking. That is, the mice carried chromosomes from two males, rather than the usual assortment of genetic material from one male and one female.

The study was published online in Biology of Reproduction.

To end up with animals doubly endowed with biological dads but lacking a biological mum, Richard Behringer at the University of Texas M. D. Anderson Cancer Center in Houston and his colleagues started with fibroblasts taken from the fetus of a male mouse, and reprogrammed them into induced pluripotent stem (iPS) cells.

When grown in culture, due to errors in cell division, about 1% of the cells from this line lost their Y chromosomes. Those rare cells containing just the original male mouse’s X chromosome were then injected into blastocyts — early-stage embryos — from normal female mice. The embryos were then transplanted into surrogate mice, who gave birth to female mice with chromosomes coming from the blastocysts and the iPS cells.

These females were chimeras — that is, animals composed of cells from at least two different genetic origins. Since reproductive cells contain only one set of genetic material, some of the chimeras’ eggs contained just the single X chromosome from the original male animals’ iPS cells.

That meant, finally, that when the chimeras mated with a normal male, the DNA would segregate such that some of the offspring would have DNA from those iPS cells and from this lucky new male who got to just have some normal sex. And voila – two dads!

“It has been a weird project, but we wanted to see if it could be done” in mice, Behringer told the Wall Street Journal.

The researchers say the technique could be used to combine traits of two males – for example, in livestock breeding programs. They even claim, optimistically, that someday it might be possible to simplify the protocol and fine-tune iPS cell technology to create offspring from either two fathers or two mothers. The hurdles to applying the technique to humans, though, are extensive — starting from the complexity of the process, the difficulty in translating mouse iPS work to humans, and the need to find a way to avoid the chimera step, which is an ethical minefield.

Image: A chimeric mouse with pups that carry the agouti coat color gene from embryonic stem cells. From NIH.