Selfish DNA facts for kids

Selfish DNA is a special kind of DNA that acts a bit like a "freeloader" inside an organism's cells. It has two main features:

• It makes more copies of itself and spreads throughout the organism's genome (all its DNA).
• It doesn't help the organism survive or have babies. In fact, it might not do anything useful at all, or it might even cause problems.

The idea of selfish DNA came up in 1976. A scientist named Richard Dawkins wrote about it in his book, The Selfish Gene. This was when scientists started to learn about DNA that doesn't make proteins. In 1980, two articles in the science journal Nature talked more about this idea.

Think of it like this: regular DNA helps a cell work and grow. It makes copies of itself by controlling the cell. But selfish DNA just uses the cell's tools to make more copies of itself. It does this without helping the organism in any other way.

It can sometimes be hard to tell the difference between selfish DNA and useful DNA. It's also not always easy to tell selfish DNA apart from some types of viruses.

How the Idea of Selfish DNA Started

The idea that some parts of our genes might not be helpful to an organism isn't new. Scientists have been thinking about it for a long time.

In 1928, a Russian scientist found a special X chromosome in a type of fruit fly called Drosophila obscura. He thought that if there were too many female flies, the whole group of flies might die out. This was an early idea of a gene that might not be good for the whole group.

Later, in 1941, scientists thought that genes from the mother (in mitochondria) and genes from both parents (in the cell's main nucleus) might have conflicts. This could lead to plants that can't make pollen, which is called cytoplasmic male sterility.

Around the same time, other examples of "selfish" genes were found. For example, a scientist studying maize (corn) found special parts of chromosomes that made sure they were passed on more often to baby plants. This is called "meiotic drive." It means a gene gets passed on more than the usual 50% of the time.

In 1945, a Swedish scientist named Gunnar Östergren talked about how some chromosomes might spread just because they are "parasitic." He was talking about B chromosomes in plants. He said these chromosomes often don't help the plants at all. Instead, they just live like parasites, helping only themselves.

Then, in the early 1950s, Barbara McClintock discovered "transposable elements." These are pieces of DNA that can move around in the genome. They are some of the most successful types of selfish DNA. For her amazing discovery, she won the Nobel Prize in Medicine or Physiology in 1983.

Images for kids

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  Transposable elements can copy themselves in two main ways: by making an RNA copy first (like "copy-and-paste") or by cutting themselves out and pasting into a new spot ("cut-and-paste").

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  Genes are not always passed down in the same way. For example, genes in mitochondria are usually passed down only from the mother.

See also

In Spanish: ADN egoísta para niños