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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!

Did you know that some biologists believe that there was once a time when DNA and proteins didn’t exist, and RNA did all the work of genetic material AND enzyme? There are many reasons to argue both why this could have been the case and why the cells of the world decided that protein and DNA were the “wave of the future,” But that’s an article for another time. It’s called the “RNA World Hypothesis,” and if you’re interested let me know. If there is enough interest, I’ll write a little introduction for your investigation on the topic.

Anywhoo, One reason for this hypothesis is the fact that there are so many different types of RNA that range in duties from genetic material to enzyme even in today’s cells. In fact, I can promise that there are hundreds of RNA molecules doing both of those jobs in YOU RIGHT NOW. I think it’s not only important to be familiar with the different types of RNA, but also to be familiar with the hypotheses as to why they work why they do. But without further hold up…

THE GREAT RNA LIST:

1. mRNA – Messenger RNA is a photocopy out of the library reference section (nuclear DNA). It carries all the same information as the DNA original, but the DNA remains in the nucleus and the ribosomes are in the cytoplasm. Just like you cannot check out a book from the reference section in a library so that it can be both ACCESSIBLE to another individual who wishes to use it and so that it can REMAIN PROTECTED, a cell cannot allow the genetic material to leave the nucleus. So mRNA acts as the photocopy. Here’s something to think about as well: mRNA is the only type of RNA that codes for protein. Everything else has some sort of regulatory function.
   
2. rRNA – Ribosomal RNA is a modern day example of RNA acting as an enzyme. If you read my article on translation, then you already know that the ribosome is the site of protein synthesis. It “translates” the information from RNA to Polypeptide. But what you didn’t know is that the ribosome is made of RIBOnucleic acid (and some protein, but mainly RNA). It catalyzes the peptide bond between amino acids, forming the polypeptide. When RNA acts as an enzyme, scientists refer to it as a “ribozyme.”
   
3. tRNA - think of Transfer RNA as an envelope that delivers amino acids. When you send a letter in the mail, you can’t simply drop the letter in the mailbox and expect it to go where it needs to. The tRNA molecule is the envelope that carries the amino acid molecule to the ribosome.
   
4. tmRNA – Transfer/Messenger RNA is a really cool RNA molecule. I had never heard of it before I started writing this article, but I wish I had. tmRNA is only found in bacterial cells, but in those cells, it acts like the refferee for translation. Check this out: When a ribosome gets stuck on an mRNA molecule for some reason, the tmRNA molecule (and some other proteins) unstuck the ribosome, put a marker on the unfinished protein so it can be destroyed, and destroy the mRNA molecule so that this doesn’t happen again. It breaks up the fight.
5. snRNA – From what I’ve found, there isn’t a lot that’s known about Small Nuclear RNA, other than that it’s composed of short RNA strands that can be found in the nucleus… who woulda thunked it? However, scientists have shown that this type of RNA molecule is involved in the splicing (cutting out) of introns from mRNA transcripts as well as the regulation of some transcription factors.
6. snoRNA – Small Nucleolar RNA is not to be confused with snRNA; it is found in the NUCLEOLUS, rather than the nucleus. In vertebrates, snoRNA is made from those introns that get spliced out of the mRNA transcript during transcription. They modify RNA nucleotides and they mark the length for rRNA molecules that are being synthesized to form ribosomes.
7. miRNA – MicroRNA molecules are usually only 19-25 bp in length – unusually small for a nucleic acid transcript. They play very specific roles in the cell, though. I’m sure you’re already well aware of the fact that stem cells can become any type of cell, and that the type of cell that they become depends on which genes become expressed in that cell. MicroRNA molecules can assist in this differentiation process by binding to the 3′untranslated region (UTR). MicroRNAs bind to regions on the mRNA transcript that match exactly, and they block translation. The cool thing about miRNAs is the fact that one miRNA can bind the 3′UTR of hundreds of genes, so the expression of a few miRNAs can block the ability for a cell to express the genes to become all but one type of cell.
   
8. siRNA – Small Interfering RNA molecules are much like miRNA molecules in that they are very small (~21 bp) and that they keep mRNA transcripts from being expressed. However, siRNA molecules come from outside RNA. Cellular RNA only exists as one-stranded molecules. When a cell encounters double-stranded RNA (viral), it chops it up into ~21 bp lengths (~2 twists of helix). It then attaches one strand (antisense) of the molecule to a protein called DICER. Using this siRNA as a template, DICER floats around the cytosol looking for mRNA molecules that are complementary. If it finds one, then that mRNA molecule is probably viral, so the cell destroys it. Cool Stuff!
   

Simply for the sake of ease, I put the most commonly taught RNA molecules in BOLD font. These are the likely suspects that your teachers will want you to know in introductory biology.

Guess what. These 10 don’t even scratch the surface. There are hundreds more classes of RNA out there, but you’re gonna hafta do your research if you want to know anything about them. But if you wish to be a kind soul, you could go look some up and post the name and description as a comment below. I’m sure your fellow nerds would be very appreciative.

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Best of Luck,

Grey

Hey Nerds,

I was talking to a family friend who owns a contracting business. It’s a family-owned company, and problems are always in abundance.

He was telling me about one particular instance in which half of the blueprints for a project that he had been commissioned to complete had gone missing. Of course, my sciency mind wandered (construction talk is frightfully boring) to genetics. Then, BOOM, epiphany.

Just for now, think about cells as a contracting company. The genetic code will act as a blueprint (I know that I contradict myself in a later post, but go with me here).

In this instance, a dominant allele will code for one copy of the blueprint. A recessive allele will code for a blank piece of blue paper.

So, lets look at the possibilities:

Homozygous dominant (XX) has two copies of the blueprint, and therefore has no problems building the house.

Heterozygous (Xx) has only one copy of the blueprint and one sheet of blank blue paper. The project takes longer, but the information is still at least there. And the house still gets built.

Homozygous recessive (xx) have no copy of the blueprints. This contracting company cannot build the house, so the lot that the house would have been built on remains in its default state: undeveloped.

Hopefully this will help some of you get a good grasp on the difference between dominant and recessive. When you get deeper into bio, you’ll find that it’s not actually that simple. But for all intensive purposes, this is all you need to know right now.

Best of Luck,
Grey