Dr. Myers posted a good basic (very basic) explanation of how we figure out what happened to a chromosome or genome of a species evolutionarily. He kind of oversimplifies it and I disagree with this method of discussing biology, but I can see it being useful tool to teach concepts to those without much of a background in evolutionary biology. I encourage everyone to keep up with Dr. Myers' blog here as he frequently posts some good stuff.
Now for the bad; it's not secret among those that know me I absolutely hate the news media for their constant mistakes when dealing with science. The AP recently had a story dealing with evolutionary biology in which the statement was made "Scientists unearthed a skull of the most primitive four-legged creature in Earth's history" which is not so bad in and of itself is not the worst in the world. It was, in all likelihood, not the first species of vertebrate with four legs. It continues to speculate about the behaviors of the animal and it's evolutionary history and lineage future. The one on ScienceNews is far more accurate and contains less speculation. Just compare the two articles and see for yourself.