If humans and apes did indeed share a common ancestor, then it would make sense that two chromosomes

There’s something fascinating about our chromosomes. We have 23 pairs. Chimpanzees and gorillas, our closest living relatives, have 24. If you come to these facts cold, you might think this represented an existential montgomery county real estate crisis for evolutionary biologists. If we do indeed montgomery county real estate descend from a common ancestor with great apes, then our ancestors must have lost a pair after our lineage

montgomery county real estate branched off, some six million years ago. How on Earth could we just give up an entire chromosome.
A close look at our genome and the genome of our close relatives reveals that we didn’t. We just combined a couple of them. Every now and then, chromosomes montgomery county real estate fuse. This fusion occurs as sperm and eggs develop, as pairs of chromosomes fold over each other and swap chunks of DNA. Sometimes two different chromosomes grab onto each other and then fail to separate.
Scientists have observed both humans and mammals with fused chromosomes. Chromosomes typically have distinctive stretches of DNA in their center and at their ends. From time to time, scientists will find an individual that’s short a chromosome, but one of the chromosomes it retains now has an odd structure, with chromosome endings near the middle and other peculiar montgomery county real estate features.
This might seem like a fantastic mutation–something like a human and a horse being joined into a centaur. Remarkably, however, fused chromosomes are real, and there are surprising number of normal, healthy people carrying them.
If humans and apes did indeed share a common ancestor, then it would make sense that two chromosomes fused in our ancestors. The rise of genome sequencing allowed them to test that hypothesis. They found that human chromosome two bears the hallmarks of an ancient montgomery county real estate chromosome montgomery county real estate fusion , with remnants of chromosome ends nestled at its core. In 2005, it became possible to test the hypothesis again, when a team of scientists sequenced the chimpanzee genome and could compare it to the human genome. The chimp genome team were able to match human chromosome two to two unfused chromosomes in the chimpanzee genome.
Ken Miller, montgomery county real estate a biologist at Brown who was an expert witness in the 2005 Dover creationism trial , includes montgomery county real estate this research in his lectures on evolution. Here’s a video of one of those lectures, where he lays out some of the evidence with impressive clarity.
What makes evolutionary biology such a fun subject to write about is that it does not stay still. While Miller’s description is entirely accurate, the past five years have rendered it obsolete. Last month, Evan Eichler at the University of Washington and his colleagues published a study in the journal Genome Research in which they deeper montgomery county real estate into the history of our missing chromosome .
They montgomery county real estate were able to do so thanks to the publication montgomery county real estate earlier this year of the gorilla genome. A comparison of the human, chimpanzee, and gorilla genomes confirms that the ancestors of gorillas branched off from the ancestors of chimpanzees and humans about ten million years ago. Humans and chimpanzees then branched apart later. A comparison between all three species provides a clearer picture of what our chromosomes montgomery county real estate looked like before they fused, and how they’ve changed since.
The bands correspond to segments of each chromosome.

The colors represent the two ancestral chromosomes (I’ll just call them green and red to keep from getting bogged down in confusing numbers). The hash marks represent regions of very unstable DNA. These areas, which are full of repeating sequences, are prone to accidentally getting duplicated, expanding the chromosome. They’re also where chromosomes are likely to trade chunks with other chromosomes. That’s why the red chromosome has a little green at the end. It had picked up part of the green chromosome earlier than the common ancestor of us, chimpanzees, and gorillas.
Three key events are illustrated here. First, the top of the green chromosome flipped (another common type of mutation, called an inversion). Then a chunk of yet another montgomery county real estate chromosome got stuck to the end of the green chromosome, marked here in pink. And then a new piece of DNA got stuck at the end of the green chromosome, known as StSat, and marked here as a yellow dot.
The ancestors of gorillas montgomery county real estate then diverged from the ancestors of chimpanzees and humans. They underwent some ten million years of independent evolution, during which time a lot happened. For one thing, the cap on the green chromosome got duplicated and pasted onto other chromosomes, including the red one, and even on the other end of the green one itself. In the illustration below, the yellow and pink segments, along with the adjoining green segment, are represented by a brown oval:
The chromosomes at the right of the figure montgomery county real estate show you what our two chromosomes looked like before they got fused. When the human and chimpanzee lineages split, each lineage inherited them. And in each lineage, montgomery county real estate they evolved