BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: natural selection

Unnatural Selection: The Future of The Future?

Imagine it’s Saturday night, you are snowed in until the morning and you need a way to pass the time. Like many people, you resort to Netflix. Upon browsing through the vast selection of horror, comedy, and romantic films, you decide you are in the mood for a documentary. Scrolling through the options, you stop at a title that grabs your attention: Unnatural Selection.

Since you are an AP Biology student, you immediately connect the words “Natural Selection” to the work of Charles Darwin, the study of genetics, and most importantly: evolution. In brief, natural selection is the survival and reproduction of the fittest, the idea that organisms with traits better suited to living in a specific environment will survive to reproduce offspring with similar traits. Those with unfavorable traits may not be able to reproduce, and therefore those traits are no longer passed down through that species. Natural selection is a mechanism for genetic diversity in evolution, and it is how species adapt to certain environments over many generations.

If genetic diversity enables natural selection, then what enables unnatural selection? Well, If natural selection eradicates unfavorable traits naturally, then unnatural selection essentially eradicates unfavorable traits or promotes favorable traits artificially.

The Netflix docuseries “Unnatural Selection” focuses on the emergence of a new gene-editing technology named CRISPR (an acronym for “Clustered regularly interspaced short palindromic repeats”). CRISPR is a revolutionary new method of DNA editing, which could help cure both patients with genetic diseases and patients who are at risk of inheriting unwanted genetic diseases. The two pioneers of this technology, Emmanuelle Charpentier and Jennifer Doudna, recently won Nobel Prizes in Chemistry for their work on CRISPR.

CRISPR illustration gif animation 1

Animation of CRISPR using guide RNA to identify where to cut the DNA, and cutting the DNA using the Cas9 enzyme

CRISPR works with the Cas9 enzyme to locate and cut a specific segment of DNA. Scientists first identify the sequence of the human genome, and locates a specific region that needs to be altered. Using that sequence, they design a guide RNA strand that will help the Cas9 enzyme, otherwise known as the “molecular scissors” to locate the specific gene, and then make precision cuts. With the affected region removed, scientists can now insert a correct sequence in its place.

Using the bacterial quirk that is CRISPR, scientists have essentially given anyone with a micropipette and an internet connection the power to manipulate the genetic code of any living thing.

Megan Molteni / WIRED

CRISPR is just the beginning of gene editing, introducing a new field of potential gene editing research and applications. But with great power comes great responsibility — and great controversy. Aside from the obvious concerns, people speculating the safety, research, and trials of this new treatment, CRISPR headlines are dominated by a hefty ethical dilemma. On one hand, treating a patient for sickle cell anemia will rid them of pain and suffering, and allows their offspring to enjoy a normal life as well. However, by eliminating the passing down of this trait, sickle cell anemia is slowly eliminated from the human gene pool. Rather than natural selection choosing the path of human evolution — we are. We are selecting which traits we deem “abnormal” and are removing them scientifically. Although CRISPR treatment is intended to help people enjoy normal lives and have equally as happy children, putting evolution into the hands of those evolving can result in more drastic effects in the future.

For our generation, CRISPR seems like a magical cure for genetic diseases. But for future generations, CRISPR could very well be seen as the source of many problems such as overpopulation, low genetic diversity, and future alterations such as “designer babies.” Humans have reached the point where we are capable of our future. Is CRISPR going to solve all of our problems, or put an end to the diverse human race as we know it? Comment how you feel down in the comments.

 

Spice: a mustard plant’s version of Off!

Have you seen me recently?

According to a recent study, the spicy flavor in mustard may be a evolutionary technique of certain wild mustard plants to repel pests.

Scientists investigated two genotypes from the same mustard plant species (Boechera stricta) in the Rocky Mountain, one from Montana and one from Colorado. The two types of mustard plant had unique spices due to “regionally distinct chemical compositions” (Daisy Yuhas, Scientific American). The mustard plants were specifically selected because their habitats had not changed much over thousands of years, allowing researchers to consider both genetic variation and existing environmental factors.

The researchers were able to pinpoint the chemical compounds that caused the differing spicy taste of the two plants. The gene BCMA encodes for an enzyme’s activity. Variations in the gene would produce either the spice of the Montana mustard or the Colorado mustard.

The scientists then planted the two mustard genotypes  in both locations, observing the plant death rate and the way local insect populations reacted. The results?

In the Montana site, the local plants repelled insects and thrived as usual in their natural environment. However, the plants imported from Colorado were not so lucky; they were attacked by insects and had a hard time surviving. These results suggest that the Montana mustard plants possess a spice tailored to deterring pests. It is likely that a mutation in the BCMA gene, and consequently the distinct spice, was so successful in survival for a certain group of plants, that through natural selection the mutation became common in the Montana mustard plant population.

On the other hand, in Colorado, insects ate both the local plants and the imported Montana plants. Possible reasons for this indiscriminate behavior of the insects include a higher spice tolerance among Colorado insects and a more competitive environment in Colorado due to a larger population of insects struggling to find food.

Conducting an additional field experiment, the scientists engineered a close relative of the Boechera stricta species, the Arabidopsis, to express the BCMA genes of the Colorado and Montana mustard plants.  They found that while the spicy compounds deterred some pests, bacteria, and viruses, they increased “susceptibility to others” (Yuhas).

The research of these scientists has provided evidence of natural selection influencing a species’ variation over time.

Now there is something to think about the next time you stare down at your mustard-covered hot dog!

Comments welcome.

Article Sources:

http://www.nytimes.com/2012/09/04/science/different-varieties-of-mustard-plants-have-unique-spice-genes.html?_r=0

http://www.scientificamerican.com/article.cfm?id=mustard-spice-evolution

How Old Are You, Polar Bear?

 

Some Rights Reserved: http://www.flickr.com/photos/xrayspx/3969642331/sizes/s/in/photostream/

Do you remember where mammals have DNA? (hint- it isn’t just in the nucleus)

Mammal cells have DNA in both their cell nuclei and their mitochondria. While DNA in the nucleus is a combination of both parents, mitochondrial DNA is inherited directly from the mother. (For more information about nuclear DNA and mitochondrial DNA download: www.cbc.ca/fifth/2008-2009/the_girl_in…/dna-definitions.doc)

And what does this have to do with the age of Polar Bears?

Well, according to a recent article in the New York Times, scientists have been surprised to find that polar bears are not so closely related to brown bears as previously thought. For years, scientists thought that the polar bear specie evolved about 150,000 years ago. Adaptations, probably due to natural selection, include white fur and webbed paws – both of which are very helpful in the icy Arctic.

Researchers Axel Jenkle and Frank Haler, of the Biodiversity and Climate Research Center in Frankfurt studied 19 polar bears, 18 brown bears and 7 black bears. After analyzing the nuclear DNA of polar bears, they believe that brown bears and polar bears began taking different evolutionary paths as much as 600,000 years ago.

The old, incorrect, theory was based on mitochondrial DNA. The mitochondrial DNA of polar bears and brown bears are very similar.  Because polar bears live on ice, and there aren’t many fossils saved in the icy arctic, it has been difficult to trace the evolution of these famous white bears.

Now scientists are trying to figure out why the mitochondrial DNA of brown and polar bears is so similar. One hypothesis is that polar bears mated with brown bears during time of global warming or climate changes. There is some evidence of the bottleneck effect, which helps support this theory.

 

Link to main article: http://www.nytimes.com/2012/04/20/science/polar-bears-did-not-descend-from-brown-bears-dna-study-indicates.html?_r=2&ref=science

 

 

from single cell to multi-cellular

Have you ever wondered how single cellular organism evolved into multicellular organisms? In a recent New York Times article, some scientists decided to see if they could get single cellular organisms to somehow evolve into multicellular ones. The problem that they thought of was that in multicellular organisms there are many cells which die so that the entire organism can live on. Why single cell organisms would group together with other single cell organisms just to die for the new multicellular organism was puzzling.

They designed an experiment where they had yeast in flasks of broth where they were being shaken for a day and then left alone for the yeast to settle. Then a drop of the settled yeast was taken and transferred to a new flask where the yeast could continue to grow. This process was continued and would allow the yeast which had evolved to be the densest and to settle furthest down to be carried to the next flask. after a few weeks the scientists observed that the yeast was falling faster and was becoming cloudy at the bottom. When looked at under the microscope the scientists found that the yeast had evolved into snowflake shaped clumps of hundreds of yeast cells stuck together. These cells were not just unrelated clumps since when separated individually, cells would recreate these snowflake shaped clumps. This property of clusters of single celled organisms to make a multicellular like organism is not special to yeast. Another organism called choanoflagellates is a single celled organism that also exhibits these traits.

One of the more amazing parts about this was that to reproduce, branches of the snowflake clump would break off after growing too large. When looked at closer they found that a section of the cells near the branch commit suicide to separate the branch to allow it to grow into a new clump. Being able to create multicellular organisms that had cells willing to commit suicide for the rest of the organism in a matter of weeks was amazing and could mean that the history of single celled organisms evolving into multicellular ones might not be as complicated as previously thought. Even though this form of natural selection was done in flasks, the natural environment could have preferred multicellular organisms over single cellular organisms for a number of reasons.

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