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The origin of living organisms on earth (McGraw Connect, 2011) is one of the biggest mysteries of the world. Chapter 25 gives us a fairly basic understanding of species and macroevolution. The first three sections of the chapter set the scene for section four, Evolutionary Developmental Biology. These sections discuss species, all some different types, how they arise (speciation), and at what rates all of these things occur. Evolutionary Developmental Biology encompasses all of that into an exciting field of science
Now, what is Evolutionary Developmental Biology? First, for short, let’s call it Evo-Devo. Evo-Devo is the science that compares the development of different organisms in an attempt to understand ancestral relationships between organisms and the developmental mechanisms that bring about evolutionary change. It mainly consists of the exploration of genes that control the development in organisms. It is fairly knew because only recently (few decades) have scientists become more interested in the similarities and differences between closely and distantly related species. This was due to the fact of increasing knowledge in the subject by focusing on related topics, and the exponential increase in technology that make the research possible.
The first topic the section stresses is developmental genes. These developmental genes are extremely important to the phenotype of the organism and the evolution of many traits. Gene changes affect traits in an organism that can then be acted on by natural selection, eventually changing a species. Also, the way the genes are expressed is important in the way new traits come about. Pattern formation, the process that gives rise to plants and animals with a particular structure, is the result of these developmental genes working and carrying out tasks in an organism such as cell division, cell migration, cell differentiation, and cell death.
The text then goes on to give an example of how these developmental genes in organisms change the phenotype of that organism due to gene expression. The example was given of the chicken and the duck. The chicken has non webbed feet and the duck has webbed feet. The difference in their foot structure is due to different expressions of the same two cell-signaling proteins BMP4 and Gremlin (Drm). The BMP4 protein is expressed throughout the developing limb and causes cells to undergo apoptosis. The Gremlin inhibits BMP4 from working, allowing cells to live. In the chicken, Gremlin is expressed throughout the limb except in between each digit, which causes the foot to not be webbed. On the other hand, in the duck, Gremlin is expressed everywhere, resulting in webbed feet! To expand upon this phenomenon, scientists have tried inserting Gremlin protein into the interdigit regions of the chicken … it was born with webbed feet!
Another important aspect of this chapter talked about Hox genes. In animals, Hox genes are a class of genes involved in pattern formation in early embryos (an example of a developmental gene class). Hox gene is short for homeobox containing genes. These genes have been very important to scientists in observing trends among large groups of species. These genes are found in all animals; this shows that Hox genes have originated very early on in animal evolution! It is believed that variations in Hox genes may have started the formation of many new body plans. Although every organism has them, the number varies per organism. The more the Hox genes, the more complex the organism is. When there are many Hox genes in an organism, they occur in clusters. As an example, mammals’ Hox genes have thus far duplicated twice to create four clusters that are all somewhat different. There are about 38 genes in total.
Developmental genes also are important in the concept that controlling relative growth rates of different parts of the body during development will cause genetic variation in organisms. Heterochrony is the term that describes evolutionary changes in the rate or timing of developmental events. Heterochrony can cause two main things. One is it can cause different species with morphological changes (e.x. human and chimpanzee skull- different parts grow at different rates). The second is it can affect the development stage at which a species reproduces. This can happen in two ways. Either the parts of the body associated with reproduction develop faster than the rest of the body, or reproduction occurs at the same known time, but non reproductive parts develop slower. Both of these examples will cause paedomorphosis.
Paedomorphosis is the retention of juvenile traits in an adult organism. A fascinating example of this is a girl named Brooke Greenberg. She is currently 18 years old, but looks and acts like a 9 month baby. Scientists have named her syndrome “Syndrome X”. They have been searching her DNA for any kind of abnormalities, such as a gene mutation, that may have caused this to happen to her. The discovery of the cause of her abnormality could very well be the key to the so-called “fountain of youth” !!
Quick vocab review (bold words in summary):
1. Species: A group of related organisms that share a distinctive form in nature and (for sexually reproducing species) are capable of interbreeding.
2. Macroevolution: Evolutionary changes that create new species and groups of species.
3. Evolutionary Developmental Biology: A field of biology that compares the development of different organisms in an attempt to understand ancestral relationships between organisms and the developmental mechanisms that bring about evolutionary change.
4. Speciation: the formation of new species
5. Phenotype: a description of traits that an organism displays
6. Pattern Formation: The process that gives rise to a plant or animal with a particular body structure.
7. Gene expression:The process through which cells can detect and respond to signals in their extracellular environment. In multicellular organisms, cell communication is also needed to coordinate cellular activities within the whole organism.
8. Apoptosis: programmed cell death
9. Hox Genes: In animals, a class of genes involved in pattern formation in early embryos.
10. Heterochrony: Evolutionary changes in the rate or timing of developmental events.
11. Paedomorphosis: The retention of juvenile traits in an adult organism.
Powerpoint Presentation: (done)
I have made a powerpoint presentation that has all of the same information as the Prezi. This is a more straight forward way to read over the information for chapter 25.4. It is made to study from.
1. Here's some more information about Brooke Greenberg. She is the 18 year old who suffers from paedomorphosis. This means that she has retained juvenile traits even though she is 18 years old. She has the mental capacity of a 9 month old and the physical appearance of a 13 month old. The first link is an article that gives basic information about Brooke and her condition, along with a picture of her and her sisters. The second is a video all about Brooke which has many more details. The third is a pubmed article that goes into detail about the salamander. In chapter 25.4, the salamander is talked about as a the most well known organism that tends to exhibit paedomorphic traits. In this particular experiment, scientists were trying to identify how a paedomorphic brains develops.
4. Webbed feet hands are not only a trait in ducks! Some humans have webbed feet and hands, but most would like them removed. This article talks about humans with webbed feet and how to "repair" them.
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