Inheritance may be far more complex than Mendel ever expected. This year marks the 150th anniversary of Gregor Mendel's publication that helped launch the field of modern genetics, and now we're looking back at just how complex genetics truly are.
Mendel, the Austrian monk, spent eight years cross-fertilizing tens of thousands of pea plants. By picking species with a handful of visible characteristics that occurred in two easily identifiable forms, Mendel was able to pinpoint what he called "factors." This revealed how the plants passed along their genetic information to the next generation.
Today, though, we know that inheritance is far more complex than what Mendel saw in his pea plants. But how exactly are traits passed from one generation to the next?
What we know is that some of our genes come only from Mom. Mendel believed that parents contribute equal numbers of factors to their offspring-and if we focus on DNA in the nucleus, it looks as if he is correct. The nuclear DNA is bundled into two sets of chromosomes with one coming from Mom and one coming from Dad. But mitochondria, which are the organelles that generate the cell's energy supply, have their own DNA that comes only from Mom. This means that your mitochondrial DNA is likely the same as your mother's, grandmothers, great grandmother's and so on.
We also know that the environment has the potential to trigger molecular changes that pass from one generation to the next-something Mendel didn't account for. Now we know that it may be possible for environmental stress to trigger small RNA molecules that reduce the activity of specific genes. This gene silencing process, known as RNA interference (RNAi), may help organisms adapt to changing conditions.
Genes can also tag along for generations. Some genes are close enough together on the same chromosome that they frequently get passed along together. Genes on completely different chromosomes can also get passed down in groups if they work together in some way to increase an individuals' chance of surviving.
These new findings in genetics allow researchers to better understand the genetic history of people, and help them focus on genetic diseases and their treatments. While Mendel may not have known everything there is to know about genetics, he gave the scientists of today the start they needed.
