Chapter 6 - Peeling Back the Layers

In the beginning, Shubin basically explains what most biology students already know: animals that are very diverse look similar when they are embryos. He also tells of the findings of Karl Ernst von Baer, who discovered that all organs in a chicken embryo were identified to a specific layer of tissue. Once he and his partner figured this out, he began to look for the same pattern in other animals--and he was right.

When I got to the part where Shubin describes how our basic shape forms, I was pretty confused. The picture on the next page helped a little, and the diagram on page 103 was even better (looks a little like ET though!). We have three main layers that form: 1) ectoderm, which forms the skin/nervous system; 2) endoderm, which has the inner structures of the body; and 3) mesoderm, which has much of our skeleton and muscles. Hilde Mangold was able to find a tiny piece of tissue that, when cut and reattached, would form twins. This, of course, was the DNA.

Shubin started to talk about DNA again, and he lost me a little. DNA is a hard concept to grasp. I eventually figured out that the structure of DNA responsible for mutation is called the hox gene, which appears in every animal with a body. Shortly after the hox gene was discovered, scientists searched for the chemical that produced the entire body plan. Finally, Richard discovered the director of genes: the Noggin. The Noggin does not actually form anything; rather, it works with other genes. The Noggin actually goes to the cells at the "top" and turns the signal off that makes them "bottom" cells.

To be honest, this chapter was as difficult, if not harder, to understand than the DNA chapter. Was it just me, or did anyone else find this hard to understand?

~Megan Hsiao(: