Even cloning has its limits, when dozens of knees have been cloned

Mice has been cloned in Japan in animal experiments from one generation to the next for so long that finally some kind of upper limit was found for cloning – the quick death of the mouse.

The work started already in 2005. Yamanashi University researchers then cloned a female mouse. The purpose was to continue cloning for a long time from one generation to the next. So they cloned the clone back into a clone.

Serial cloning produced the same effect as copying the same image over and over again on a photocopier. In the first copy, the quality of the image decreases slightly. When duplicating a copied image, the quality deteriorates further.

Researchers transferred the nuclear DNA of the clone into the oocyte of a mouse from which the original nuclear DNA had been removed.

The birth rate of such clone mice started to decrease in the 27th generation.

Cloning continued for as many as 57 generations, every three or four months. A mouse’s pregnancy usually lasts about 19–21 days.

1,206 clones were produced, all females, he says news agency Reuters.

Over two decades later, researchers obtained mice already in the 58th generation.

These mice had already accumulated so many genetic mutations that they lived a short life, only days, the researchers report.

This it was the first time that a mammal has been serially cloned for this kind of research. The purpose was to study clones and mutations from one generation to the next, says website Science Alert.

“For a long time it was unclear whether the mammal species could be maintained only with the help of clones,” writes the geneticist Teruhiko Wakayaman led by a team of researchers.

Plants and some simple animals have been kept alive from generation to generation with the help of clones.

One model predicted that asexual mammalian lineages would inevitably accumulate deleterious mutations in animals.

In the end, so many mutations accumulate that when cloning in a series, the generation collapses, i.e. dies of mutations.

FOR a generation Up to 25 cloned mice looked no different from the original clone. This led scientists to wonder if animals could be cloned indefinitely.

Then everything changed. Successfully cloned mice began to be born less and less from generation to generation.

It seemed that the clones lost their ability to treat chromosomal abnormalities. The X chromosome became a problem after the 25th generation of clones.

The number of deleterious mutations almost doubled by the 57th generation. The mice carrying the mutations still lived a normal lifespan up to the 58th generation.

Clones previous generations could perhaps be produced by normal inbreeding. The researchers normally mated females that were clones of generation 20, 50 and 55.

In generation 20, the pups were like normal mice. The cubs of knees 50 and 55 were small. Eventually the litter size of these clones also increased. Mammals could perhaps withstand mutation in this way.

The study was published by scientific journal Nature Communications.

Mammalian was first cloned in the mid-1990s. This cloned sheep Dolly caused a sensation.

Since then, scientists have learned a lot about cloning. For example, clones have been produced using different cell types.

There are conservationists who hope that cloning could help protect animals. One day animal species could perhaps be brought back from the brink of extinction this way.

There are people in the public who have cloned their beloved pets.