Vocabulary: reproduction 詞匯: 生殖，繁殖

What's wrong with having three parents? I'm happy with two but maybe it would have been a case of the more the merrier.

The role of parents is not only to give us love and guidance, but also to pass on genetic code.

A few particular healthy genes would be the contribution of the third parent, according to a British government decision to support a ground-breaking technique for preventing genetic disease.

It has to do with the mitochondria, the energy factory we have in our cells. They contain just 37 genes and sit outside the nucleus which has more than 20,000 genes. Diseases caused by faulty mitochondria are serious and are passed down the maternal line in the egg, so the technique being pioneered by Newcastle University involves using healthy donor eggs.

After fertilisation, the genes of the father and the mother would be transferred from the embryo to the healthy donor egg, which has had the genetic material from its nucleus removed but still has good mitochondria.

To explain the technique, scientists in Newcastle compared it to changing the battery of a laptop computer. Like in the hard-drive, nothing changes in the DNA of the two parents because they are in the nucleus.

The government will prepare regulations later this year and the technique could be available within two years. Faulty mitochondria affect one in every 6,500 babies and it can cause lack of energy and result in muscle weakness, blindness and heart failure.

Some people are opposed to this because they consider it unethical and say it could set the UK on a slippery slope. The nightmare of creating a Frankenstein's monster is always in our mind. They also say that couples with the problem could adopt a child instead.

But the same was said when the world's first test tube baby, Louise Brown, was born in Britain in 1978. And the only Frankenstein we see is in the movies.

The fact is that families are changing all the time. Who knows what the typical family will be like in 50 years' time...