about alan

Dr. Alan Christensen is a professor and researcher at the University of Nebraska, Lincoln. Alan grew up in what is now Shoreline, near Aurora Village. Through 3rd grade, he went to school near Sea-Tac, but this was before I-5 was built so the commute was hard for his parents. His mother, Edith, decided she would start a school in North Seattle, instead. That school was Evergreen, just down the road. Alan and his sister were the very first students enrolled at Evergreen. 

Alan has always liked science and was curious about how things worked. He had a simple electronics kit and made an AM radio on a circuit board that could tune into a nearby station really well. He didn’t like the station much, but it was like magic to pull in the sounds from thin air. He also had a chemistry set and liked to make different colors, but was disappointed that nothing in it would burn or explode. He went to Lakeside from 7th through 12th grade , where he fell in love with chemistry (and was Mr. Rona's classmate!). He went on to major in Chemistry at UW, but came to realize that he didn’t want to be a professional chemist. After being offered a summer job in a lab at UW’s medical school, Alan decided to pursue a PhD in molecular biology, and it was then that he found his lifelong interest in DNA and genetics. When he’s not researching or teaching, Alan enjoys woodworking. He’s made furniture and is restoring a cabin, but also makes bowls and tool handles with his lathe.

First, a bit of background and vocabulary to help us understand Alan's research. DNA is a long, connected strand of molecules (four different types, repeated in varying patterns) that gives instructions for the development and maintenance of living things. All living things have DNA, but the instructions for the development and maintenance of a human are different than the instructions for a house cat or a fern, and so the DNA sequence (the order in which its constituent molecules are found along the strand) looks different between those organisms. In total, human DNA has around 3 million of those building block molecules, and specific stretches of it with specific sequences that give specific instructions are called genes.  If one were to "read" DNA, one would encounter certain stretches that give instructions (genes, or "coding DNA"), and long stretches in between genes that don't give instructions for anything in particular ("non-coding DNA"). All the genetic information in an organism put together is often referred to as its genome. 

You may have heard the term "chromosome" before. Those are essentially storage facilities for DNA. Humans have 23 different chromosomes, and each one is distinct with different genes on it (sort of like 23 different bookshelves at a library, all with specific books in specific places). For example, in every human, you'd find the gene for eye color in the same place on the same chromosome.

The sequence of the molecules in DNA changes often due to mutations, or mistakes that occur when DNA is copied and replicated. Sometimes, these changes don't make much of a difference, but other times they can benefit the organism or result in illness or death. Occasionally, these "new" genes can get passed down to offspring, and this is part of the process of evolution.

While both plants and animals have mitochondria and use them for cellular respiration, plant mitochondria are quite different from animals’, and Alan is interested in learning more about this. One striking difference is the size of their genome. Mitochondria have their own designated chromosome, and in humans, that strand of DNA is about 16,000 base pairs or building blocks long. In plants, it can be more than a million base pairs long! Despite this huge difference in DNA material, plants don’t have many more actual genes (DNA stretches with a “function”) in their mitochondrial DNA than humans do. Another unique characteristic of plant mitochondrial DNA is that those genes evolve very, very slowly due to a low mutation rate in the genes. However, they have a high rearrangement rate, meaning where the genes fall in sequence changes often, and between different groups of plants, they are often very scrambled. So, if you went to the genetic library of one kind of plant, you'd find a certain book in a very different place on the bookshelf than with another kind of plant.

A characteristic that Alan recently published a study on is long stretches of DNA (up to a couple of thousand base pairs) that are in two or sometimes more different locations in the mitochondrial genome. Thinking back to our “library” metaphor, it would be like having the same set of several books, in the same order, in several places on the bookshelf. One thing that is hypothesized to cause these repeats is a DNA repair mechanism called “double-strand break repair”. A double-strand break is when both strands of the double helix break in one spot and have to be “stitched” back together. Plants’ mitochondrial DNA is known for being very efficient at this type of DNA repair and for doing a lot of it. 

A theory about why actually comes from a particular species of bacteria that is also very efficient at double-strand break repair called Deinococcus radiodurans. Scientists think that this bacteria became good at that type of repair because throughout its evolution it was constantly in danger of desiccation (drying out), and desiccation can cause double-strand breaks in DNA. Alan and his team think this may explain some of their findings. They found that, across groups of plants, vascular plants had much larger and more abundant repeats in their mitochondrial DNA. They think this is because being vascular exposes plants to a higher risk of becoming desiccated, particularly as a seed or spore, so they became better at double-strand break repair, resulting in more and bigger repeats in their genome.