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He said that he had been studying different species in school, but that his teacher couldn’t give him an deep enough explanation concerning the criteria for establishing one species as different from another. So, I’m going to do him a favor and answer his question to the best of my ability.

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A species is defined as a population of individuals that are capable of successfully producing offspring (children) without any scientific intervention.

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Obviously, you wouldn’t be able to have children with a parrot. At first thought, you may say to yourself, “Well, yeah. We’re of different species,” then it’ll click… we’re of different species. But what is it about being of different species that makes it pretty much impossible for parrot-people to become a reality?

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REPRODUCTIVE ISOLATING MECHANISMS – Things that prevent the formation of an inter-species baby.

There are two types of mechanisms that prevent the formation of extreme hybrid offspring. “Prezygotic” mechanisms are those that prevent sperm from ever reaching the egg. “Postzygotic” mechanisms are those that happen after the sperm has fertilized the egg; they pretty much say “Oh no. This just won’t work.”

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Prezygotic Mechanisms

• Habitat Isolation – If you and the parrot live thousands of miles apart, it’s pretty unlikely that you’ll have babies.
• Temporal Isolation – If you’re usually active at night (nocturnal), and the parrot is usually active during the day, it’s pretty unlikely that you’ll have babies.
• Behavioral Isolation – If the parrot likes it when you fly in circles, but you can’t fly in circles, it’s pretty unlikely that you’ll have babies.
• Mechanical Isolation – If the parts don’t fit, then it’s pretty unlikely that you’ll have babies.
• Isolation of Gametes – If the sperm can’t recognize the egg, then it’s pretty safe to say that you won’t be having babies.

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Postzygotic Mechanisms

• Hybrid Invariability – If the combination of your genes and the parrot genes cause the baby to self-destruct, then it’s pretty unlikely that you’ll be having babies.
• Hybrid Sterility – In this case, you and the parrot may be able to have babies, but your babies will not have the ability to have babies.

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I really hope this helps!

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Remember that post about evolution as “changes in allele frequency?” It only requires a few minutes to breeze through, but I’ll give you the sparknotes version : when the alleles in a population change, so do the individuals. BOOM, evolution.  But evolution happens over many thousands of years; how do scientists compare allele changes over _smaller time scales?

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Fitness = the contribution that an individual makes to the gene pool of the next generation relative to the contributions of other individuals.

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To condense, if I have four children, and you only have one, then I’m FOUR TIMES as fit as you. It has nothing to do with strength and nothing to do with cunning or ability to do anything. In fact, it can’t even be calculated until after you’re DEAD… how physically fit can you really be then?

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Animals who are the most fit have two defining characteristics:

• They live long enough to reproduce.
• They have either lots of kids, or they have a few children that are pretty sure to survive. This is called having “viable” offspring.

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What this does for scientists is allow them to take information about all of the individuals that were able to reproduce successfully and compare that to information about individuals that were not. From this, they can find out if there are any genetic similarities between those who were successful versus those who were not. This gives scientists a good idea about what is emerging as the evolutionary changes in a small amount of time.

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Hope this helps!

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Let’s catabolize this.

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What is an allele?

You already know that an allele is a form of a gene. Much like shoes come in all different sizes and designs, genes do as well. There’s the tuxedo gene, the air force 1 gene, the stiletto gene, the flip-flop gene, the groovy platform gene… I think you get my drift.

Alleles are the different forms of THE SAME genes that are floating around in the cells of individuals. For instance, baseball and top would be alleles of the HAT gene, whereas stiletto and flip-flop would be alleles of the SHOE gene.  NOTE*: There is a difference between the number and types of alleles and the number and types of genes. Learn more about alleles HERE.

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What is “allele frequency?”

The phrase “allele frequency” is nothing more than a fancy word for a proportion, or percentage, or the total alleles in a group of individuals.

For instance, let’s assume that I have ten marbles. Three of them are red, two are yellow, and five are blue. I could say that the “frequency” of blue marbles is 5 in every 10, or one half, or 50%.

Just like that, the “allele frequency” simply establishes the percentage of alleles that are floating around for a particular gene.

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Let’s put ‘em together!

So, what then, is evolution? Evolution is the result of changes in the amount of certain alleles in a population.

Alleles are forms of genes, so we know that they code for some sort of protein. Different alleles mean different forms of the same protein. It may do essentially the same cellular job, but in a little bit of a different way. When all of these alleles add up, what we see is an organism. If those alleles change, then the organism changes as well.

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How about an example?

Andrew lives in a place that only has three hundred people. Everybody is exactly the same other than their eyes. 100 People have blue eyes, 150 have green eyes, and the other 50 have brown eyes. Eventually, over thousands of years, something happens that makes the green-eyed people move away. Now, there are only 150 people in the town. 100 have blue eyes, and 50 have brown eyes.

The brown eyes allele of the eye color gene once made up only 17% of the total alleles. Now, it’s 33%. For this population of people, it can be said that they have evolved to only have blue and brown eyes… but mainly blue.

It’s a really far stretch, but it’s supposed to be nothing more than an abstract explanation. If you’re still having any problems, post them in the forum, and I’ll try to cater to your issue specifically.

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Hope this helps!

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1. Water is the most abundant chemical compound on the planet.

There are more water molecules in the breath you just took than there are people who you will EVER MEET IN YOUR LIFETIME. I can prove it.

There is one mole of water in every 22.4 liters of air at normal conditions. That means that there is approximately 5% of a mole in every liter of air. A normal human breathes about one half of a liter of air in every breath. That means that there is approximately 2.5% of a mole in every breath. Since one mole is 602,200,000,000,000,000,000,000 molecules, there are 15,100,000,000,000,000,000,000 little waters in every breath. There aren’t even half that many people alive right now.

2. Water can serve as a source of both Hydrogen and Oxygen.

If you know anything about biology, you know that without either of those elements, you wouldn’t last another hour. Both oxygen and hydrogen are necessary for running some of the most foundational cellular processes that keep you alive. A molecule that can give you both of those elements at the SAME TIME is a winner.

3. Water is a medium for almost all biological reactions.

If it happens, it happens in water. Water is just the “in” place among the cool chemicals.

But on a more serious note, water is a wonderful medium for chemical reactions because it allows solutions to be very dense. Much more dense than in air. If your body was to use air for a biological medium in the same way that it uses water, you would either be very very very large or you would always be in danger of EXPLOSION from the high pressure!

4. Water is usually inert/stable at normal Earth conditions.

Water is just smooth… and cool. It doesn’t need to go exploding all the time in order to make friends. It’s smarter than that.

For whatever reason, water has become the perfect conditions for water to exist at a fairly stable state. This means that it is possible for living organisms to use it without much risk of danger.

5. Water can hold tightly to large amounts of heat energy.

It takes a lot to get water all steamed up, but when he’s hot, he STAYS that way. Rawrr!

Water has a ginormous heat capacity, so it doesn’t change temperature very easily. It takes a lot of energy to heat water up, and water releases that heat very slowly. This is advantageous for animals especially because animals (humans included) are composed of mostly water… around 60%. The heat capacity of water makes it easier to control body heat because the water in your body doesn’t allow for rapid temperature changes.

6. Water was the habitat for life on Earth before land was.

Many scientists believe that there was a point, many millions of years ago, that all living creatures lived underwater. Of course, this was long before the Earth looked anything like it does today. Scientists think that the earth was once completely covered in water; eventually geological activity forced the sea-bottom up to the top, and land was formed.

If you’re living in water, fighting every other creature there just to stay alive or competing with everybody else to get access to food, you would have a much easier life if you could live on land. It is believed that some plants and animals were able to make the transition from water to land. Because land creatures were once aquatic, though, we still possess true needs for water as well as the ability to use water for biological reactions.

7. Water can act as both a base and an acid.

In most circles, the definition of an acid is any molecule that releases a lone hydrogen atom into solution, and the definition of a base is usually anything that can release a hydroxide ion. Since every reader of this article isn’t a biochem major, I’ll anabolize this for you.

You know that water is H2O, but that also means that it’s H-O-H. There are two hydrogen atoms and an oxygen atom. A lone hydrogen atom (H+) carries a positive charge that makes it very reactive; this charge causes the lone atom to be called an ion. Likewise, the other half of the water molecule (termed a “hydroxide ion”), carries a negative charge and is also very reactive. When either of these are very concentrated in a solution, they tend to make things happen… as far as reactions go. It gets much more complicated than I can really efficiently describe here, but trust me, the fact that water can do all of that is really significant.

8. Water is the Universal Solvent.

Ok, so everything in the universe can’t dissolve in water. In fact just today in chem class, I learned of a little trick chemists use to describe how much of a “non soluble” compound will actually dissolve. But that’s an idea for another post… and takes that idea in a completely opposite direction.

As far as animals are concerned, all of the necessary molecules are soluble. Water is the medium for ALL major body processes. It is used to regulate temperature and to be the medium for reactions throughout the body. It’s pretty darn significant… if you ask me.

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But there’s not really any surprise there… water is Chuck Norris.

Great Danes ruled the world, followed closely by Pit Bulls. There were no laws or languages. Any poor puppy that was unlucky enough to be born had to fight to remain alive 47 hours a day. (Their planet spun more slowly than ours.) Life for them was constant warfare. Anything that COULD be used as protection or as a weapon WAS.

Many dogs found that chewing on the bones of their prey could sharpen their teeth. Some other dogs found that if they didn’t eat a lot, they would lose weight, and they could move much faster. K-9 was an awful place to live… ESPECIALLY for the small dogs – those dogs that couldn’t run quickly and didn’t have sharp teeth or claws. They became very very good at hiding, though.

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One Glorious Day…

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A toy poodle found a teacup chihuahua. Stepping very lightly, so as not to be heard, the poodle creeped up behind the poor chihuahua. The poodle hadn’t eaten in WEEKS, so when he arrived close enough to the chihuahua, he GRABBED it by the tail, THREW it high into the air, and SWALLOWED it whole.

But there was something… ehh, different… about this chihuahua. This awesome little yippy dog passed into the stomach of the poodle and was UNHARMED. (Scientists are still trying to figure that one out.) While passing through the intestine of the now-uncomfortable poodle, the chihuahua became lodged in the cecum. And it STAYED THERE.

One would predict that this would cause problems for both the poodle and the chihuahua, however it benefit both parties. The chihuahua no longer had to fight a losing battle for food on K-9, and because it could digest things that the poodle could not, it helped the poodle get more nutrient from the food. Win-win situation.

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Ok, Ok, Ok, so that analogy isn’t great…

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Let’s see YOU do better. The endosymbiotic hypothesis (the fancy name for this whole shendig), is the most popular scientific theory about how mitochondria and chloroplasts came to exist for the first time.

Scientists think that at one point, they were once unique cells. They think that waaaaaaay back in the day, millions of years ago, the only creatures on the planet were single celled organisms. Germs. They ate each other. So if a cell wanted to survive being eaten, it had to figure out ways to neutralize the the predator’s attacks.

Scientists think that eventually, it just so happened that a cell ate another cell… but there was something special about this cell (*chihuahua*). The prey cell could avoid being digested by the predator cell somehow, but the prey cell could also do something that the predator cell could not. The predator cell couldn’t eat the prey cell, but it could give it nutrients and protection in exchange for whatever the prey cell could do.

When we put this in terms of mitochondria and chloroplasts, we can see that the mitochondria prey-cells had the ability to use air along with sugar to make energy molecules. (Scientists think that this was a lot more efficient than whatever the predator cells had been doing.) As for chloroplast prey-cells, can you imagine how helpful it would be for the predator cell to eat a prey-cell than could make energy from air and light… all the predator cell had to do was give it water! EASY!

SO, let’s recap:

• Mitochondria and Chloroplasts were once feeely-living cells.
• They were eaten by another cell, but they could survive digestion.
• Both cells (predator/prey) had something that the other could use.
• Eventually, the cells came to rely on each other, which lead to the birth of eukaryotic cells as we know them.
  

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Hope this helps,

Grey

One day last month, his mother came home after working a 57.5 hour shift at the factory that makes those metal bands that hold pencil erasers to wooden pencils. Thankfully, it just so happened that Jimmy’s dad was dropping Jimmy off at home before leaving for work at that very moment. (So Jimmy wasn’t left home alone at that age. We don’t want you thinking that we condone leaving children unattended.)

Mrs. Jimmy’s-Mom-Lady was exhausted. Wouldn’t you be? She wasn’t the kind of person that would take out her aggression on her child, but like any human being, she had her buttons for pushing. And like any 8-year-old coming home from school, Jimmy was easily influenced by the song of the ice-creram-truck down the street.

“Mommy, will you please take me to the corner so I can get an ice cream?” Jimmy asked, very politely.

“Mommy is very tired, Jimmy. Why don’t you sit on the porch, and the ice cream man will eventually come past the house.”

At this point, Jimmy stopped being polite and threw a tantrum. His mommy, already at the end of her string, grabbed him by the ear and locked him in the tower until his hair grew long and he decided to change his name to Rapunzel.

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Take Two

Rimmy is the eight year old alternate identity of Jimmy, who lives in a parallel universe.

One day last month, his mother came into his room after working for fifteen minutes from home. She runs a tutoring website and is very successful working from home. :) Jimmy was folding the clothes that he had earlier put through the laundry and was about to begin making dinner.

“Son,” his mother asked using a sparkling set of pure white teeth,” would you like to go for an invigorating jog and then stop by the corner at exactly the same moment that the ice cream truck ALWAYS drives past it.. without fail?”

“Why yes, mother. That would be lovely. Thank you. I shall simply finish these chores, and we shall be off!”

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What the heck does any of this have to do with transport?

How wonderful of you to ask. Jimmy and Rimmy, in these cases, are the substrates (remember that word from the enzyme article?). Their mothers played the role of the transport proteins.

In the second scene, Rimmy’s mother ACTIVELY took a role in ASSISTING her young son in MOVING to the area of some action. In this case, the acquisition of a yummy ice cream treat. Because, his mother USED SOME OF HER ENERGY to play an ACTIVE part in her son’s life, this would be an example of active transport. In a cell, this would be the movement of solutes in and out of the cell using proteins that require energy to pump these molecules across some sort of membrane wall. (Just like in enzymes, they make the movement faster).

In the first scene, however, Jimmy’s mom did NOT take her son to get ice cream. Instead, this scene was set up to highlight one specific aspect. Rather than expending energy to make the action happen (getting ice cream), Jimmy’s mom required him to wait for the action to happen naturally…. WITHOUT ANY INTERVENTION OR MANIPULATION TO MAKE IT HAPPEN FASTER. This is what we call passive transport in cells.

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SO, let’s recap:

1. Active transport: uses energy.
2. Passive transport: does not use energy.

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I hope this helps,

Grey

If you prove me wrong, I’ll be happy to give you the four large… I’ll make four million after I study you and figure out how you work.

For the rest of you, enzymes are one of a bazillion reasons you’re living. But they are the only reason that all the chemical reactions in your body can happen so fast. How fast? A few thousand times or more. For example: when your nerves send signals through your body, they release molecules that carry that signal between nerve cells. In order to set up for the next signal, any extra molecules floating around between the nerve cells have to be eradicated. Neurotransmitter-ase can completely clear out that space in fewer than one hundred milliseconds. (That’s about the same amount of time it took you to read the word “milliseconds.” )

Enzymes are so helpful because they’re so specialized. Each enzyme protein (most of them are proteins, btw) can only bind to one or only a few different molecules. They help to make reactions go faster by changing the amount of energy required to make the reaction take place. (The fancy name for something like this is a “catalyst.”)

Think about it like this. There’s a graham cracker on the table in front of you. For some reason or another, that gracker (that was actually a typo, but I think “gracker” is a good new name for it) needs to be broken apart. Nobody really knows why. Now, there’s a VERY small possibility that you could walk away and not return for 10 years, and that gracker may or may not be broken. In that time, someone else may come along and break it, an earthquake could knock it off the table, aliens with lasers could cut the entire building in half and happen to slice the gracker, or the gracker could spontaneously break all by itself…. although that last one is pretty unlikely.

Regardless, that gracker needs to be broken NOW. Maybe it’ll break without you, but maybe it wont. So, you pick it up, one side of the gracker in each hand. You twist your hands, and the gracker breaks into two pieces. GREAT JOB.

What you just did was to manipulate the mechanism of the reaction. Somehow, you figured out that if you use your hands, you can break the gracker. How smart you are! In much the same way, enzymes manipulate the way a reaction happens. By binding to the enzyme, molecules can be bent, twisted, sliced up, smooshed together, and changed in lots of different ways. BUT each enzyme can only do one thing. Just like genes, those “stupid little dumb ugly gremlins that only do what they’re told,” enzymes have only been trained in one job.

And they are SO PISSY! They will only work under certain conditions. If it’s too hot, they stop working. If it’s too acidic or too basic or too cold or if there isn’t enough substrate (the fancy word that means molecules that bind to the enzyme) they won’t work. They just sit there and complain and then fall apart. Ungrateful little… *grumblemumble…

SO, LET’S RECAP:

1. Enzymes are proteins… usually.
2. Enzymes are catalysts – They make reactions go by faster without actually being changed by the reaction.
3. They manipulate the way a reaction happens.
4. Enzymes are VERY specific – They can only bind one or a few molecules, and they only do ONE job each. (That’s why there are so many of them)
5. Enzymes have evolved to work best in very specific environments – If conditions are too (hot/cold, acidic/basic, etc.), the bonds that hold the enzyme together start to break apart and the enzyme won’t be able to work properly anymore.

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Anyway, I hope this helps!

Grey

X²

The function:

To decide whether the difference between observed and expected values is actually significant.

The example:

You’ve been told that in 1995, the average successful first kiss rate was 15%. With some digging, you found that last year, 27 of 476 young men successfully landed their first kiss in your hometown.  Is this consistent with the average?

To solve this problem:

1. You’ll want to establish all of the categories. In this problem, we are comparing kissers to missers. This is a success-failure scenario, so those are the ONLY two categories.

2. Establish your null and alternative hypotheses. If you are still kinda cloudy as to how exactly to do that, I’ll write a post on that later, which you will find HERE. But for now, just know that

• Null Hypothesis = The average 15% success rate holds true because … (insert hypothesized reason here).
• Alternative Hypothesis = Due to (insert hypothesized reason here), the success rate has changed from the 15% average.

REMEMBER: These are hypotheses. You don’t have to get them exactly right every time. That’s what experimentation is for. Essentially, the null is just supposed to say “there was no change” and the alternative hypothesis is supposed to say “there was a change.” Don’t forget what the function of a chi square test is.

3. Since you now know what is to be compared, you’ll want to make a table of expected versus observed values. I’ve taken the liberty of completing the table for this problem. Enjoy. :)

	Successful Kisses	Failed Kisses
Observed	27	449
Expected	67.35	449
(observed - expected)	-40.35	0
(o-e)^2	1628.1225	0
[(o-e)^2]/e	24.174	0

REMEMBER: You MUST MUST MUST use actual data (numbers) rather than percentages or ratios. AND don’t use the data if any of the points are less than 5.

4. Use the data you found by completing the table along with your knowledge of the X²equation to calculate the X² value. If this is the first time that you’ve encountered X², I’ve included a copy of the equation below. The sigma (the funny looking E) means that you make the calculation for each category separately and then you ADD THEM ALL TOGETHER to get the final value.

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5. Use a probability chart like the one found here to find the P value. I’d explain how to do it, but if you follow the link, you’ll see that those people do a pretty good job of explaining it themselves. Anyway, in the context of this problem, you’ll find that X²=24.174 and P<0.0005. Using the standard P> 0.05, we can compare to find that our experimental P value of 0.0005. Since our value is waaaaaaaay smaller than 0.05, we can reject the null hypothesis and conclude that THE AVERAGE KISS SUCCESS RATE IN YOUR HOMETOWN IS LESS THAN IT IT WAS IN 1995.

Boom Shakka Lakka!

If your dad is anything like mine, then every year, he whips out a set of rusty old pruning shears and goes to town on the plants around your house. By the next year, the plants are both shorter and bushier. And just a little tidbit for anybody who grows garden plants: after your plants grow about two feet tall, if you pinch off the buds of new branches, the plants will stay short but fruits will grow larger. Wanna know why? Of course you do.

I’m sure you are already familiar with primary (straight up) growth and secondary (beer belly) growth. If not, here’s a quick overview: the processes in plants that make them grow taller is called “primary growth” and the processes in plants that make them grow wider (like the rings in trees) is called “secondary growth.”

What you may not know is that primary growth is brought about by a hormone (yes, plants have those too) called auxin. When auxin is released from the apical meristem, it does a lot of things, but it mainly causes plants to grow taller and non-bushy. That’s why garden plants stay short when you pinch off the buds. (the apical meristem is the source of the hormone auxin… it’s found at the APEX, thus the name.)

But this still doesn’t explain why the plant gets bushier… why doesn’t the plant just stay at the same bushiness level as before, simply a bit shorter? This is where the Costello hormone comes in. By the way, it’s actually named cytokinin. This hormone, produced in the roots, promotes the growth of lateral buds rather than the apical ones.

Think of a christmas tree. I’d venture to guess that the plant that’s now in your head has a triangular shape (or circular pyramidal, if you wanna get technical). That’s because the thin part at the very top (the apical meristem) is producing auxin that is telling the cells around it to GROW UPWARD. as the hormone travels through the plant, though, its concentration decreases. Eventually, auxin reaches the base of the plant, close to the roots, which are readily producing cytokinins. These promote the growth of the lateral buds that become branches that are full of foliage. These cytokinins diffuse up the tree, but their concentrations also decrease as they move farther away from the roots, and this can be seen as the tapering of the tree as you get closer to the top.

Here’s another little tidbit to rot your brain: the very tip of the root is ALSO an apical meristem. So it produces auxin to make the roots grow further into the ground…. and the lateral buds do the same thing to make the lateral branches grow out away from the tree. All these hormones work in a complicated, synchronous harmony in order to grow into all the plants you see.

Plants aren’t so simple, huh?

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Grey

{Haploid . Diploid . Monoploid . Aneuploid . Polyploid . Allopolyploid . etc}

You probably won’t need to be able to define all of the terms in your classes… not for a while anyway… but once you study genetics for a while, you’ll find that these terms pop up pretty often. It’s going to be helpful to you to recognize what they mean.

That being said, the word “ploidy” describes the number of COMPLETE SETS of chromosomes in a cell. There are lots of terms derived from that word, and they all have to do with numbers of chromosomes – but they don’t all describe the number of COMPLETE SETS. It’s strange, yes, but you’ve just gotta know it.

Haploid vs. Monoploid

Most students will learn the meaning of “haploid” (one complete set of chromosomes) as the alternative to diploid (2 sets). This isn’t usually a problem until one encounters the term “monoploid,” which isn’t the same as haploid.

You see, “haploid” refers to the number of complete sets, and is represented by the letter “n.” (“n” is not a variable. You’ll see this further down, when we talk about diploid) The monoploid number (represented by x) IS A VARIABLE that represents the number of chromosomes in a complete set.

So, if I have a haploid cell of a Buhbushka Toad that only holds 6 chromosomes, then I would say that the cell is 1n (or just n) and that x=6.

Diploidy

The prefix “di-” means two, so “diploid” means two complete sets of chromosomes. It’s usually denoted by “2n.”

Let’s look at that toad cell again. If x=6 in a 1n cell, then that would be double in a 2n cell. So, in the diploid form of the Buhbushka Toad, x=12.

Haploid and Diploid are related that way. Haploid is HALF of Diploid, and Diploid is DOUBLE of Haploid.

Polyploidy

A polyploid cell has MANY sets of chromosomes. If you’re already thinking that it’s denoted by 3n, 4n, 5n, etc, then you’re incorrect. Sorry. After the diploid level, the ploidy level of a cell is denoted by 3x, 4x, 5x, etc.

There are also some terms that you should be familiar with concerning ploidy.

• Aneuploid – describes changes in the number of a PORTION of the chromosome set rather than changes in the number of sets. For instance, if half of a set of chromosomes disappeared, leaving part of the genome diploid and part of the genome haploid. (From Greek words that mean “not good” because this usually results in deformations in humans)
• Autopolyploid – recognizes that an organism is polyploid, but adds “auto-”, denoting that all extra sets of chromosomes come from the same species
• Allopolyploid – also recognizes that an organism is polyploid, but with the caveat that some of the sets of chromosomes come from a different species (not usually seen in humans)