Week 3: Connections

The main focus of chapter 3 is DNA and how bodies and species are formed from a single egg. Not only was DNA discussed broadly but the text goes into great detail about how genetics are switched on in order for them to work and for physical features to be expressed. One of the major genes discussed was named the zone of polarizing activity (ZPA). This tissue allows for the difference between the pinky and thumb. ZPA has helped gain a lot of insight in the understanding of the creation digits and toes. Although we have not discussed ZPA exactly in class, we have discussed genes that help express certain areas of the body during development: HOX genes. I have enjoyed reading this chapter due to the similarities of my (basic) understanding of embryonic development with that of the experiments that took place within Shubin's lab. This ZPA gene had a similar pattern of activity to that of the sonic hedgehog gene that we had studied during Dr. Livingstone's module in Introduction to Biology as well as retinoic acid and vitamin A. It was very interesting when all of these aspects came together within the experiments since it showed how similar developments are between species. The mirror image duplication from the ZPA tissue was very intriguing and so a picture is posted below. I like the section of the book that says the "inner fish lay in the biological tools that actually build fins". What Shubin gained from these experiments was that the different genes that Tiktaalik had to create the limbs were not new DNA but and ancient gene that was expressed. Although we have no studied a great amount of DNA expression in this class and lab, we have looked and compared DNA within many different species. We built phylogenies from genetic information, which is something that could be done with the expression of the ZPA gene. This chapter really helped me understand more of the developmental stages we briefly spoke about in class as well as helping me understand DNA linkage between many species throughout time.