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Who wins? Dar-wins!
Aside from the cheesy pun, I’m going to clear up some misconceptions about Evolution. Except for biology majors (and even then…), most people don’t even know the basics of evolution.
“Evolution” is really Evolutionary Theory, much like Cell Theory (that bodies are made of cells), Germ Theory (illness is caused by microorganisms) or Gravitational Theory (“gravity” is the force that acts on an object with mass). Evolutionary Theory is merely change over time. Evolution and Gravity are scientific theories because they can be directly observed and tested with scientific experiments. A theory is only accepted as truth until proven false. Accepting a theory as true is important for scientific progress within that field.
There are four Evolutionary Forces:
Mutation
Natural Selection
Gene Flow
Genetic Drift
“5th Force” -Inbreeding (Non-random mating)Mutation is the source of all variation. Without mutation, evolution would not occur. Heritable mutations occur at the most basic level -within the base pairs of DNA. Non-hertiable mutations (such as cancer), do not affect evolution. However, there are genes linked to cancer, such as mutations of the BRCA2 gene, and these mutations are heritable. But mutation of a skin cell in a 50 -year old male that progresses into skin cancer, is not evolution.
Natural Selection is arguably the most well known evolutionary force, due to Darwin’s studies of selection in his book On the Origin of Species. Natural Selection is the non-random survival and reproduction of genotypes and/or phenotypes. Selection is best described by Darwin’s postulates:
-Individuals within a population are variable (every organism is different)
-Some of this variation is passed to offspring (genes in the eggs and sperm)
-In every generation, there are more offspring produced than can survive
-The “best fit” of these offspring survive
*side note: “fit” in the evolutionary sense has nothing to do with physical fitness, such as strength, but rather in an organism’s ability to produce many, viable offspring.Gene Flow moves variation from population to population. For instance, a group of brown frogs that mixes and mingles in a nearby group of green frogs may result in an increase in brown frogs in the next generation for that niche.
Genetic Drift causes a decrease in variation due to random chance. One common form of drift is the “bottleneck” effect. Imagine a bottle filled with yellow, red, and blue marbles. Now imagine that bottle being tipped so that only the marbles in the neck spill out. Because these marbles are only a small representation of the bottle, it is very likely that only yellow and red marbles spill out, or only blue. This phenomenon is often seen after a natural disaster, when large populations of a species die out.
Inbreeding changes are alleles are partitioned between individuals, increasing homozygosity of the population. For example, the royal family in England saw an outbreak of hemophilia due to marrying cousins.
I give evolution 2 opposable thumbs up!
http://www.pbfcomics.com/?cid=PBF195-The_Pacific_Council.jpg
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Great advancement in science!!!
http://news.bbc.co.uk/2/hi/science_and_environment/10132762.stm
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Comment away!
Hello readers!
Just letting you know that we now have a working “comment” function installed, thanks to the help of our loyal follower Kaidon. You should follow his fashion blog located at http://kaidonjetaime.tumblr.com
Thanks! Hope everyone has a great weekend :)
- Kyle
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The Theory of Endosymbiosis
The endosymbiotic theory in biology deals with the origin of mitochondria and chloroplasts as organelles in prokaryotic and eukaryotic organisms. Specifically, it explains how they became integrated into the cell, and it defends the myriad characteristics that separate them from other membrane-bound organelles of cells.
First, let me explain the terminology. “Symbiosis” refers to a beneficial partnership between to organisms of different species working together. “Endosymbiosis” specifically refers to an identical relationship, but where one organism lives inside the other. The main idea behind endosymbiotic theory is that mitochondria and chloroplasts originated from unicellular bacteria (more specifically, the mitochondria originated from aerobic bacteria, which perform cell respiration, and the chloroplasts originated from cyanobacteria, which carry out photosynthesis). The integration of these bacteria into our evolutionary history originated with their engulfment by another bacterium, and a resulting beneficial interaction. This beneficial interaction results in the engulfed bacteria being passed on through the generations.
Photo credits: http://www.biology.iupui.edu/biocourses/N100/images/018f2.gif
The following evidence for endosymbiotic theory is outstanding!!!
- Mitochondria and chloroplasts cannot be formed de novo, they can only arise from preexisting entities.
- Think about how bacteria alone reproduce. They need to go through mitotic divisions in order to reproduce! They certainly cannot be created de novo.
- A cell’s genes do not encode all of the proteins responsible for the formation of these organelles. - Mitochondria and chloroplasts have their own genome responsible for creating those remaining proteins!
- These genomes are circular and do not contain histones, just like a bacterial chromosome. - Mitochondria and chloroplasts have their own mechanisms for protein synthesis.
- The first translated amino acid is n-formyl Methionine, just like in bacteria.
- Interactions with various antibiotics support the idea that they are descendants of bacteria.
The coolest recent display of endosymbiotic theory is in Elysia chlorotica, an algae-eating slug from the northeastern United States. Not only does it eat algae, but it also steals the chloroplast from the algae in its digestive system. It utilizes the genes in the chloroplast to carry on photosynthesis, and as such, does not need to eat in order to survive! Invertebrate biologist John Zardus says, “This could be a fusion of a plant and an animal - that’s just cool!” What are your thoughts on this plant-animal hybrid???
-Kyle
Sources:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Endosymbiosis.html
http://learn.genetics.utah.edu/content/begin/cells/organelles/
- Mitochondria and chloroplasts cannot be formed de novo, they can only arise from preexisting entities.
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Whale Falls
If beached whales are so rare, what happens to whales when they die? Actually, an extraordinary thing happens. The whales sink to the ocean floor, and can sustain their own ecosystem for up to 50+ years. This phenomenon is called a “Whale Fall.” In benthic ocean communities, food is a huge limiting factor. The organisms that live down there have adapted to be able to feed off of almost anything; this is a key factor in their survival.
Once the original carcass of the whale has been depleted (by a wide range of organisms), chemosynthetic bacteria starts to dominant the area. This type of bacteria works similarly to chlorophyll, but instead of using CO2 as the starting material, these organisms use sulfur. This kind of bacteria can exist on its own, or it can live inside other organisms. They use the sulfur in the whale bones and convert it into organic compounds. A new type of polychaete worm has actually been discovered, and it lives solely on whale falls. The chemosynthetic bacteria lives inside of these worms, and the worm then uses the organic material produced by the bacteria as a food source.
One interesting thing about the worms is that they are all female. This fascinated researchers because they could not figure out how these worms reproduced. What they found out was that the male is extremely small compared to the female, and lives inside the female, near the reproductive organs. This adaptation is a perfect example of the wonders of nature: since these worms only live off of whale falls, it would expend a lot of energy for the worms to hunt out food and a mate.
Since whale falls have only recently been discovered and are hard to reach, new facts are constantly being found out about them. Keep an eye out for new research coming out about whale falls!
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X Chromosomes & Genetic Mosaicism
X-Chromosomes. Everybody’s got one! Or two. The X chromosome is so fascinating to study because in most cases, multiplicity of chromosomes is a huge problem. Case and Point: Down Syndrome, sometimes called trisomy 21, because of the multiplicity of chromosome 21. This chromosome is actually extremely small, and just one extra causes a cascade of problems in the body. So how does the female body deal with the extra X? After all, it’s an extremely large chromosome, full of important information. The solution: Barr bodies! In every cell of the female mammal, one X-chromosome randomly “shuts down.” The DNA becomes methylated, basically wound down into a squished up package of genes. This occurs sometime during embryo formation. When it occurs is actually somewhat random as well. More on that later. So, one chromosome gets shut down. How do the cells then replicate? Well, before mitosis starts to begin, the Barr body becomes acetylated, and voila! The chromosome is ready for replication.
The interesting thing is, mom and dad’s contributing X-chromosomes are shut down with equal probably. EXCEPT, in the case of the placenta. The cells of a female fetus closest to the placenta will shut down their X-chromosome received from dad. The common thought of why this happens has to do with protecting the fetus from mom’s immune cells. Perhaps if the cells more closely resemble mom’s, the fetus is more protected.
Another consequence of Barr body shut down is in the case of heterozygosity for X-linked traits. Assuming that Barr body shut down is random, all heterozygotes for a particular X-linked trait will exhibit a sort of mosaicism. The most common example of this is the tortoiseshell cat. The allele for cat color is located on the X-chromosome, and cats can be either orange or black. (Of course, other colors and patterns exist, and multiple genes contribute to cat color; however, for the sake of this article, we will just stick to the main ones.) Since male cats have only one X-chromosome, they can only be orange or black. For a heterozygous (with respect to color: an orange X and a black X) female cat, Barr body inactivation leads to a spotted appearance of both black and orange fur. Calico patterns form when Barr body inactivation occurs earlier in gestation. (The white color is derived from a genetic phenomenon called epistasis, which will be discussed in a later article). The embryo is smaller, and therefore, the patches of color are larger. Once a Barr body is formed, that same X-chromosome will be inactivated during the remainder of the cells life, even after replication. Additionally, the replicated cells will also exhibit the same Barr body. A male tortoiseshell is extremely rare; in fact, the only way a male cat can be tortoiseshell is if it is Klinefelter: XXY.
For the human case, mosaicism exists in a condition of the sweat glands, hypohidrotic ectodermal dysplasia. And here’s the shocker: IT’S X-LINKED!!! Persons with this disorder fail to produce functioning sweat glands. Females heterozygous for this disorder will form patches of functioning and non-functioning sweat glands. A living mosaic.
Barr bodies are one of the hottest lines of research right now, and though they are extremely interesting, there is still much to be discovered about them. If you leave this article remembering only one thing, just keep this term in mind: “mosaicism.”
Kelsey Maxwell
Intern, UTeach program
Marine and Freshwater Biology (B.S.)
The University of Texas, Austin -
Welcome to Our Blog!
Hello, and welcome to our blog! If you’ve stumbled upon this blog you’re either extremely bored, super passionate about science, or being blackmailed. Whatever your motivation - we are happy to have you.
We are two undergraduate biology majors at The University of Texas at Austin who are extremely passionate about science. While our passion lies mostly in biology, we (occasionally) find other scientific subjects very interesting!
Our goal is to spread our passion for science. The blog posts will not necessarily always cover innovative research and topics, but rather will discuss and share our passion for things we have learned in school. Genetic mosaicism and X-chromosome inactivation is our favorite topic and therefore will be our first post in the blog. It’s only fitting, after all, since a conversation on this topic is what led to us becoming such great friends.
So again, we welcome you, and hope you enjoy what you find. Feel free to leave comments, questions, or anything else you would like to share. If you find any inaccuracies in the information we share with you, please let us know! While it is our goal to post about our interests, we are still biologists-in-training, so we might not get it completely right the first time.
Sincerely,
Kelsey & Kyle
