AP Biology class blog for discussing current research in Biology

Author: k2l2

How Old Are You, Polar Bear?


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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:…/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.


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Identical but Not the Same


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After studying genetically inherited traits and diseases it could be easy to assume that genes determine everything about us. While it is true that colorblindness is a sex-linked trait – there is certainly more to the story.

Monozygotic “identical” twins are genetically identical, so they should be the same in all ways shouldn’t they?

Why, then, does one twin get early onset Alzheimer’s disease and the other “identical” twin doesn’t? The same is true for height, autism, and cancer. Although, when one twin has a disorder the other is more likely to get the disease also, that is not always the case.

In the January edition of National Geographic, author Peter Miller discusses the newest theories about how genes, environoment and epigenetics affect our life (and the end of it).

Twins offer scientists a unique opportunity to study how genetically identical people differ. Basically, that means scientists can study how things other than genes affect human development and lifespan. Already, scientists have found that a persons height is only 80% determined by genetics because the heights of “identical” twins differ by about .o8 on average. Using IQ tests, scientists have nearly disproved John Locke’s Tabula Rasa or blank slate theory (the idea that children are born with a blank mind that is either stimulated – (and made intelligent) – or not –  (kept unintelligent)). Specifically, scientists studied twins who had been separated at birth and adopted into different families. In this way, scientists have found that intelligence  is about 75% controlled by genetics.

So that leads to the question, what is it besides genes that affects us humans so drastically?

Environment has something to do with our differences. However, that cannot be the whole story. “The Jim Twins” as they are called in the twin science community, were studied in the 1870’s. They were adopted into different families where both boys were named Jim. Then went on to have the same jobs, marry wives of the same name (two Lynda’s first then two Betty’s), enjoy the same hobbies, enjoy the same brand of cigarette and beer, name their sons James Allan and James Alan… the list goes on. These two lived very similar lives, yet they grew up in very different environments. If environment isn’t the only factor in creating difference then what is?

Scientists have recently come to believe that epigenetics plays a significant role in our lives. Epigenetics (site 2) can be seen as the meshing of environment and DNA. In the words of author Peter Miller “If you think of our DNA as an immense piano keyboard and our genes as keys – each key seach key symbolizing a segment of DNA respinsible  for a particulare note or trait, and all the keys combining to make us who we are – then epigenetic prcesses determine when an how each key can be struck changing the tune.”  Environmental changes do have some impact.  When a pregnant mouse is put under stress during the pregnancy it can create changes in the fetus that lead to abnormal behavior as the rodent grows into adulthood.

However, scarily enough, many epigenetic changes appear to occur randomly (thus creating a probelm for the organized nature/nurture theory). Currently work is being done studying DNA methylation, which is known to make the expression of genes weaker or stronger. Specifically, Andrew Feinburg, director of the Center for Epigenetics at Johns Hopkins School of Medicine, is working to find how DNA methylation relates to autism. Currently, he is using scanners and computers to search samples of DNA from autistic twins who have the disease in varying degrees. He is looking to compare how and why

the genes are expressed differently.

In the end, all we know is that there is more to our future than our genes can tell us. Yes, our genes play a huge role in who we are as people – in terms of appearance, character, intelligence and more – but there are some variables that our environment and epigenetics control.

Main Article: Miller, Peter. “A Thing or Two About Twins.” National Geographic. Jan 2012: 38-65. Print.

That’s Disgusting!

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Have you ever watched something so gross you just have to make a face?
Scientists are studying disgust and how it may have helped us evolve into a clean, healthy, and surviving race.

Disgust isn’t just a learned behavior, as I assumed. It begins very early- as you can see on the faces of  these babies who are eating lemons for the first time. And the grammar school taunting of “you have cooties” is a hurtful taunt because the labeling evokes a small sense of disgust in the other children toward the child being teased. It is the disgust, and to a very small degree, the feeling of being shunned that creates the kindergarten tears.

Though teasing puts disgust in a negative light, it has done wonders for the human race.  According to Dr. Valerie Curtis from the London School of Hygiene and Tropical Medicine:

“[Disgust] is in our everyday life. It determines our hygiene behaviors. It determines how close we get to people. It determines who we’re going to kiss, who we’re going to mate with, who we’re going to sit next to. It determines the people that we shun, and that is something that we do a lot of.”

In other words, disgust partially defines who we spend time with, how we maintain ourselves and who we do not spend time with. Because we have a sense of disgust, we humans have kept ourselves clean enough to thrive in this bacteria filled world. Pregnant women are especially sensitive to disgust, especially in the first trimester, when fetal development is most fragile. It is also the time when the mothers immune system is the least strong. For these reasons, the mother’s emotional way of warding off disease — disgust —  is strengthened.

The emotion of disgust stems manly from the insula and amygdala. The insula, a “prune sized,” centrally located “slab of brain tissue,” causes many of the social emotions, including guilt, pride, and humiliation. The amygdala, similarly, is connected to human emotional responses, especially fear and pleasure.

Since disgust has show to be such a key factory in our motivation to stay clean, and healthy, Dr. Valerie Curtis (quoted above) along with other pubic health activists have been “trying to gross people out” in the name of hygiene. Through cartoons and pubic advertisements, the activists are aiming to invoke a sense of disgust in the current, unclean practices. The programs currently exist in Africa, India and England. Who knew disgust could be so helpful?

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SALT: Hate it or love it? Either way you can blame your parents.

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As a salt hater myself, I find it hard to understand why my grandmother pours salt over salads, soups, even “bland” sandwiches. Why she seasons all her food so that it tastes like salt water was always a mystery to me.

So why DO some people like salt while others hate it?

The answer may lie in what parents feed their children between the ages of two months and six months- sometimes unknowingly giving their children food with lots of salt.
According to the study, infants who ate only baby food and other natural foods like fruits and vegetables (all of which contain little or no salt) during their first six months disliked or were indifferent to salty foods by preschool age. On the other hand, the children who had consumed salty foods in infancy preferred salty foods over food without salt. Unfortunately, these children tended to adore unhealthy, salty foods like potato chips, French fries, hot dogs and pretzels.

The good thing about consuming salt is that it is necessary for humans to function properly.
For example, humans need salt to make the digestive acid, hydrochloric acid. Also, oftentimes it is mixed with iodine – another element necessary for human life. In the late 900’s, salt was worth its weight in gold in many African kingdoms simply because it is so vital.

So how much salt is too much?

On average, a person needs to consume about 500 mg
day. However, most americans consume ten times that amount.

We Americans have trouble consuming too much salt. Too much salt can lead to hypertension and heart attacks. Normally, the kidney filters the blood so that excess salt will be released in the urine. However, when people eat huge amounts of salt, some of the excess remains in the bloodstream. For some people, the increased salinity in the blood causes blood pressure to rise to unsafe levels. Unsafe because, as we learned in class, hypertension can lead to heart attacks and strokes.

So, for most babies it is better when the parents stick to low sodium foods, especially since the infants showed no preference for salt at two months, meaning that my grandmother, and other “salt lovers” probably aren’t born with their love of salty foods. Salt “loving” seem to be a behavior that, once moulded between the ages of 2 and 6 months, has lasting effects on that person’s preferences.


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Ever wondered why your GPS speaks in a female voice?

iPhone 4S is "Female"

Ever since the new iPhone came out just last week, Siri has become the newest technological innovation on the market. Siri acts as an assistant: “someone” iPhone users can talk to, who can book reservations, and who can even schedule appointments. It seems like the first step toward electronic friends!
Before Siri was purchased by Apple it spoke in a “gender neutral” voice: a voice that was neither male nor female. However, Apple changed that setting. In five of the seven countries that offer the iPhone 4S the voice is female. GPS devices also default to a female voice- except in Germany where a BMW GPS was recalled because men refused to “take directions from a woman.”

But did you ever wonder why your Siri and GPS systems speak in a female voice?

Studies have shown that female voices are preferred over male voices. This preference starts before birth. Fetuses react when they hear their mother’s voice. However, fetuses do not react when they hear other female voices or their father’s voices.

Furthermore, stereotypes play a role. In American history, female voices have been the radio operators. It was women who gave directions to pilots in World War II. Similarly, women have conventionally taken on the role of secretaries and communicators. As a result, GPS systems and Siri systems are taking on a female voice for roles that have been traditionally female. Furthermore, in American movies woman usually take on the role of the “good witch” or other positive character, while evil characters often have a deeper, more masculine voice. However, when the culture is different the stereotypes change, the voice gender may change too: as exemplified by the masculine GPS default language in Germany.

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Laugh Until It Hurts!

Have you ever left a funny conversation feeling better than ever? Have you ever felt a special bond with those who can easily make you laugh?

A recent New York Times article discussed why laughter feels so good, even if you laugh until your stomach hurts.  Laughing causes the release of endorphins which is an opioid, or morphine-like chemical.

As a result of the release of endorphins, laughter acts as a “painkiller.” Recent studies show that humans have a higher pain tolerance for intense skiing workouts, an ever-tightening blood pressure cuff, or ice packs on the skin after laughing at either a stand-up comic, or a funny movie. “Feel –good” movies, or nice movies that do not make the viewer laugh, do not have the same pain-reducing effects.

So why, then, is laughter contagious? Laughter has been found to be a bonding activity, much like singing or dancing (which also trigger the release of endorphins).  People feel connected when they laugh together, and, according to Dr. Dunbar, laughter was probably “an early mechanism to bond social groups.”  That other primates, such as apes, bond over laughter (which sounds like a human pant) and the joint release of endorphins, adds validity to Dr. Dunbar’s theory.

So, do you think this study is convincing enough to get “funny movie” time before sports practice?


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