Summary for Your Inner Fish CH3
Although it is interesting that we can trace homologous structure back to common ancestors, it is very interesting that we can trace back the gene frequencies, finding the small changes which result in easily visible differences between species today. Our bodies are formed from one single cell, which carries the plans for our entire body. Within this cell is all of the DNA which is passed from our parents, from their parents and so on. DNA makes up genes, which make up chromosomes, which make up cells, which turn into a body. Hands are very complex structures, which contain three different dimensions: thumb and pinky side, top and bottom, and tip and base. The million dollar question is what change in DNA causes these differences. The answer lies in the embryo, but is impossible to study this on human embryos, so the answer was chickens. A number of biologists did countless hours of work with chicken eggs to prove that each small change within the embryo causes a major difference in the mature body.
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