DNA tells us who’s who

By Claire Curry | Published Thursday, January 6, 2011

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Last month we went far afield from our usual discussions of bird habits and identification and talked about what makes a bird. I’d like to continue this month by telling you more about DNA.

DNA is the information that encodes life. It is made of four molecules called nucleotides that occur in many combinations to specify different proteins, which make up the bodies of all organisms.

DNA is interesting to more than just molecular biologists. For scientists studying populations of critters or plants, we can also use it to look at how the organisms are related to one another and even get clues as to how they are interacting.

How does this work?

The genetic code, four different chemicals called nucleotides, is the same in all organisms. The genome (all the genes) of say, a chickadee, contains different areas. Some are genes that code for proteins, the building blocks of all organisms’ bodies.

Genes also have regions that regulate when they are used (because other molecules can bind to them and stop or start the reading of the DNA).

Then there are areas that have no apparent use. Some are old genes (no longer used) that have been copied due to errors in replicating the DNA (so only the new copy is used), some are viruses that have inserted their own DNA in the chickadee’s DNA, and some are just repeating sequences that have no known function.

Changes can occur in the nucleotides making up the sequence when the DNA is copied imperfectly when the chickadee reproduces. The areas that are not currently in use can change a lot faster over the generations than genes that code for important proteins. It won’t hurt the baby chickadee if these variable DNA sequences change a little bit more. If a useful gene changes, it might randomly change to something harmful, something neutral, or something better. Most often it will be neutral or harmful.

If it changes to something harmful, that chickadee’s genes either won’t get passed on to the next generation or it won’t pass on as many as its more successful cousins. So, those genes tend to stay the same.

So what can we use those quickly-changing areas of the DNA to tell about birds and other critters or even plants? If you have two birds, you can compare how related they are. Because DNA is made of two strands, sometimes each strand has its own variant of the DNA sequence.

So, if you look at the baby chickadees in a nest, you can see one variant from one parent and one variant from the other parent.

If you end up with a baby chickadee that has a variant not found in either parent, then you know that it has a father that is not the father feeding it. Scientists have used this to discover that many species of birds that we once thought were models of familial harmony actually have additional partners on the side.

You can also compare these variants between populations of birds (or whatever other critter you are interested in). If you compare the same area of DNA, sometimes different species will have different variants that are unique to their species or population. Then you can do several really neat things.

First, if two species are very similar, you can tell if an individual is a hybrid between the two (i.e., it has one parent from each species) or just individual variation within a species. One strand of DNA will have one group’s variant while the other strand has the other’s variant if it is a hybrid.

You can also have an unknown bird (or a feather with a bit of blood still in the tip – the DNA can be extracted from that) and compare it to DNA from known bird specimens and identify what species it is. Scientists have also used this to find that populations of some birds are distinct from one another even though their plumages are almost identical.

Once a sufficient DNA difference is found (remember, there are small variations in any population, even between parent birds and their young), scientists can look for other differences in song and behavior to determine if it should be classified as a different species.

This has happened many times now with birds, other animals and plants too.

Isn’t it amazing what insights we can get about the birds that we love to watch, by examining the molecular information within them? It’s made life very exciting for scientists who study populations and species of all organisms, from birds to frogs to bugs to flowers to trees.

It adds a new dimension to our knowledge and understanding of the natural world by giving us insight into creatures’ relationships to one another.

Even if you are still a bit fuzzy on the details, the take-home message is that the living things in our world are intriguingly complex. As you are enjoying the birds at your feeders, the trees in the forest and the grass on the ground, think about what amazing wonders, both big and small, that we share the world with!

The next monthly field trips to the Lyndon B. Johnson National Grasslands are Jan. 5 and Feb. 2. We will depart at 9 a.m. from the Forest Service district office in Decatur. For more information, contact Mary Curry or the Forest Service at (940) 627-5475.

Claire and Mary Curry are nature enthusiasts based in Greenwood. If you would like to contact them, e-mail them at

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