My Personal Science Nerd

Hey Nerds,

In biology lecture this week, my class is covering the mechanisms of evolution. I needed some extra practice, so what better practice than to explain the concepts to someone else. LUCKY YOU! Here goes…

It should be pretty obvious that there’s a serious amount of diversity on Earth – even among individuals of the same species… in the same population! But, life happens. And when the situation changes, sometimes individuals in a population can’t deal with those changes. You already know that when this happens, we call it natural selection. Those individuals that can still deal with the environment after the situation has changed are the ones that we say have been “selected for.”

With that being said, there are three ways that this can occur:

Stabilizing Selection

Remember what we said about there being a lot of diversity? Think about it like this: there are three strains to a species of butterfly (white, gray, and black). The white and black butterflies are what we would refer to as the extremes, and the gray is what we would call an intermediate. Makes sense, yes? Most populations have divisions like this (with extremes and intermediates).

In the case of stabilizing selection, the strains selected for are usually the intermediates. It STABILIZES the species. In terms of our example, this would mean that something is keeping white and black butterflies from being able to survive and reproduce very well. The species is stabilized as mainly gray.

NOTE: this doesn’t mean that there’s any loss of ability to produce offspring that land in the extreme category. Those butterflies can still be produced. However, they don’t have many children.

Directional Selection

Can you guess how this mechanism of selection works? Here’s a hint: it leans toward one direction. To be specific, this means that selection favors ONE extreme over both the other extreme AND the intermediates.

So, if there was some sort of factor that kept black AND gray butterflies from being able to survive and reproduce as well as the white butterflies, then it could be said that selection favors the white butterfly. Because the white butterfly is an extreme, this would be a form of directional selection. It would also be directional selection if the favored butterfly was black.

Disruptive Selection

So now that you have a pretty good idea of how this kinda works you probably know the only other way that this can work.

In the case of disruptive selection, both of the extremes are selected over the intermediates. NO GRAY BUTTERFLIES. It’s kinda like double-directional selection. I can’t think of anything creative at the moment, but you’re a smart person. You can think of something.

.

I hope this helps.

.

Best of Luck,

Grey

Continue reading

directional, disruptive, evolution, natural selection, selection, stabilizing, traits

“Blah Blah Blah Natural Selection. Blah Blah Blah Evolution. Blah Blah Blah Mutation. Blah.”

That’s actually written in my notes. Looking through some of my old notes to write this article, I found that quote and it was too good to pass up. Thankfully, I’ve grown a bit since then, and I can better explain this stuff to you (but of course, with the same teenaged angst).

As far as vocab terms go, “genetic variation” is one of the most straightforward ones that you’ll run across. For those of you who are a little slower than others, it means “VARIATION in a population based on GENETIC differences.” Are we all together here again?

Here’s something to keep in mind: you can’t tell differences in genetic variation by simply looking at an individual. Sure, you can look at hair color or eye color, and you’ll probably already know that these differences are based on genetics. BUT not every trait is genetic. Extreme “buff-ness,” for example is a trait that almost all members of the bodybuilder population have. Unfortunately, that’s not based on genetics. THEREFORE, we have to make a difference between GENOTYPE and PHENOTYPE. If you don’t see how that ties in right at this moment, that’s ok… it’s just something to keep in mind.

Discrete Characters vs. Quantitative Characters

Let’s talk turkey. Let’s say, for instance, that there exist only three genes in turkeys: one for feather color, one for gender, and one for everything else. For now, we’re gonna ignore the “everything else” gene and hone in on the other two.

The result of the gender gene is what we’d call a DISCRETE CHARACTER. It’s only got a certain number of results: male or female. There’s not really much of any middle ground there, so it’s a discrete characteristic.

The result of the feather color gene would be understood as a QUANTITATIVE CHARACTER. Although it’s possible that in some species color is either black or white (in which case, it would be discrete), but in most species, colors are the result of a few pigments blending together to give a certain final result. Like the range of browns (from almost white to almost black) in human skin, quantitative characteristics are usually part of a gradient.

If you’re ever having trouble assessing whether a characteristic is discrete or quantitative, ask yourself “are there only a few possibilities for this trait or are there only a few?”

Here’s an example: Is foot size a discrete or quantitative characteristic? (technically this is a trick question, but just follow me here) Because human adults show foot sizes that range from super small to super large, it’s pretty obvious that there are more possibilities than black vs. white. So foot size would be a quantitative character.

Average Heterozygosity

This is going to be the shortest paragraph I’ve written thus far. Average heterozygosity is the percentage of genes in a genome that are heterozygous. Boom. That’s all. If a population of Granny Smith apples had 500 genes, with heterozygosity in around 150 genes, then it could be said that that population has an average heterozygosity of 30%.

It’s actually that simple. But here’s the catch: it can’t measure variation any smaller than whole genes. If there was a mutation in a gene that changed the sequence but NOT the final result, using average heterozygosity would completely overlook that.

Nucleotide Variability

That’s why they invented nucleotide variability. Here’s how it works. Pick one individual from a population; compare his/her genome sequence to that of another individual from the same population. Do this again… A WHOLE LOT. Record results. What this does is tell scientists how much variation there is in the genomes of the population.

For instance, in a population of iPhones, it was found that there are approximately 122 million base pairs in the genome. After comparing the sequences of numerous iPhones, it was observed that any two iPhones differ on average by about 61 million pairs. Therefore, the average nucleotide variability among iPhones in that population was around 50%.

Other Sources of Variation

Those are the big boys that you should really be familiar with, however there are a few others that you should at least recognize.

Geographic Variation – brought about by changes in location that force populations to change in isolation from one another.

Cline – form of geographic variation. However, this is characterized by a gradient between numerous locations. If the percentage of people with a gene for black hair were to increase gradually as you move from Los Angeles to New York, that would be referred to as a cline.

Mutation – The ultimate source of all new alleles. The introduction of new characteristics due to random chance.

.

I really hope this helps someone. Be sure to comment.

.

Best of Luck,

Grey

Continue reading

average heterozygosity, cline, evolution, genetic, mutation, natural selection, variation

Earlier I did an article informing you about the Earth’s atmosphere. Well, now I feel that an article should be written about a topic that is equally as important: the layers of the Earth.

When you think about Earth, at least the non-atmospheric portion of it, you get the image of a big round ball of rocks and water. That, to a certain extent is true. But what is on the inside of our planet aside from a wonderful personality. Is Earth just a shallow ball on the inside that is waiting to collapse in on itself or it’s it composed of different layers that in turn are composed of different element and compounds? If you were to guess the latter of the two ideas then you would be correct. Either way, I still think you should read this article.

So, I will start off by listing the different layers of the Earth and then will go more in depth as we proceed through the article. The Earth is composed of four basic layers: crust, mantle, outer core, and inner core. Each of these layers are vastly different from each other and are always changing, sometimes very violently, as time continues. The first and outermost layer is called the crust. This is the ground you walk on or the ocean floors. The second layer is the mantle. This layer is the thickest of all the layers (when the outer and inner core are not combined). The core is what follows the mantle. The core can be broken into two layers: the outer core and the inner core.

Starting from outside and going inward: crust, upper mantle, lower mantle, outer core, and inner core.

As mentioned earlier, the crust is the outermost layer. It is made up of two types of plates: continental and oceanic. As you scan the crust, one would find that it varies in its thickness, ranging from roughly 5 km to 70 km thick. The locations where the crust is thicker is the continental plates whereas the thinner portions are the oceanic plates. Earth’s crust is mainly a composition of alumino-silicates, which are minerals made of aluminum, silicon, and oxygen.

The second layer is called the mantle. The mantle is roughly 2900 km thick and can be divided into the upper mantle and the lower mantle. A majority of our planet’s internal heat can be found in the mantle.     Because of this heat, convection occurs which allows for plate tectonics to take place (I will discuss that in another essay). In the upper mantle there exists what is called the asthenosphere. This part of the mantle is soft and plastic. Pressure is the cause for its characteristics. On top of the asthenosphere is the lithosphere. This layer can both include the uppermost regions of the mantle as well as the crust. The lithosphere is what is broken up into the tectonic plates. I will talk about the stress that is placed on it later when I do seismology. The mantle is composed of Fe,  Mg, Al, Si, and oxygen silicate compounds. In the mantle, the temperatures are extremely hot, ranging from roughly 500 to 900 degrees Celsius and increasing to well over 4,000 degrees Celsius as you approach the core.

The third layer is called the outer core. The outer core is roughly 2300 km thick and made up of a nickel-iron alloy which is in its liquid form. The temperatures in this part of Earth’s interior can soar to around 6100 degrees Celsius. As I mentioned earlier, the outer core is composed of nickel-iron alloy which is able to influence the Earth’s magnetic field due to eddy currents, or Foucault currents, which help to protect us from the solar winds that the Sun emits. Additionally, the reason this alloy is not solid is because the pressure is not strong enough to make it so.

The last layer is the inner core. This solid layer of the planet is the innermost and hottest part of Earth, with temperatures possibly reaching the temperatures as the surface of the sun. It is thought to be composed mainly of iron, this being based off of the abundance of chemical elements in the solar system.

This concludes my article about the layers of the Earth. I will go into the mechanics of seismology in a later article. Thanks for reading!

Photos came from Wikimedia Commons.

Continue reading

core, crust, Earth, layers, mantle

Ok, so I was going to write an article over cloud formation and dynamics but Grey pointed out the Black Saturday brushfires in Australia and I figured that it was an interesting topic to write about and you will see why in this post. I will get back to my normal posts after I write this. Also, I will be posting articles that will go more in depth over some of the environmental/meteorological/climatological/etc topics that are embedded within, so wait for those posts if you want a detailed and simple (I know, it’s a paradox) explanation.

The Black Saturday brushfires of Australia was a devastating event that started on February 7th, 2009 and lasted until March 14th, 2009. Brushfires in Victoria, Australia are not uncommon, in fact there have been many brushfires ‘outbreaks’ in Victoria but non as devastating as this one. Victoria has the perfect climate for the dangerous brushfires

It is believed that the fires were started from different sources but mainly lighting and arson. Because of the climate of Victoria and the weather patterns, both prior and during the event, were the main cause for the outbreak. That year there was an extensive period where the rainfall amounts were dangerously below average. This was the long term cause for the brushfires. With respect to short term causes, the days leading up to the event as well as the days that followed displayed unusual and special meteorological conditions: high temperature, low humidity, and strong winds made for a deadly combination that fueled the fires.

In addition to the meteorological factors, there were numerous other factors, such as vegetation. Of course the vegetation factor can be linked to issues concerning the weather. As a result of little rainfall, the vegetation dried up and thus was able to serve as firewood.

During the actual event, the winds were one of the greatest problems to people. A method that is commonly used when fighting wildfires is back-burning. This is where you burn the vegetation that is in the path of the fire in order to contain it and prevent it from spreading onward. But the winds prevented this from being an effective method to end the destruction because it would change the path of the fire. In addition to changing the path, the winds would carry embers to other areas. Obviously this can cause more brushfires to occur and increase the destruction and the power of the system.

Now, one might ask the question of whether this is a result of global climate change or not. Some sources say that a link can be made while others argue against that claim. There is much more that needs to be uncovered within this event as well as global climate change. But it is known that water problems was a major cause for the drought in Australia and things are forecasted to become worse. With the water problems and drought-like conditions increasing in severity the brushfires in Australia will only become worse.

There is so much left to understand about this tragic event. Hopefully, as we discover more about the fires we will be able to prevent such horrors as this from happening. As for now, do your best to prevent wildfires from starting. It is really quite sad when nature is destroyed by such a preventable occurrence, and even sadder when communities, families, and lives are torn apart and burned by it.

Continue reading

Australia, Black Saturday, brushfire, bushfire, drought, dry, fire, rain, wildfire