Genes and Alleles

Hey guys! Welcome to this video on Genes and Alleles.

In this video we will take a look at what genes and alleles are, as well as their functions.

Often times, when we want to know what something is, we want a very specific answer. Like, what is an atom? An atom is literally the smallest unit of chemical matter. Well, that’s really specific. Why can’t all answers be that simple, and that specific.

Once these small units of matter begin to build on one another, we start to get into complex systems that work together to build other things. Well, genes are a result of that. Genes are made up of other things. So, in order to answer the question, “what are genes?” We have to know what those other things are. In this case, we must first have a basic understanding of what DNA is.

First, let me give a general answer to the question, “what is a gene?” then we will go into a little more of the specifics.

Genes, Alleles, and Dominance

A gene is literally just referencing a very specific portion of your DNA. However, that specific portion is a full instruction to make something in your body. There are around 25,000 genes in the human body. So, you can think of that as having 25,000 different complete instructions on how to make something.

It may be helpful to think of it in this way. Let’s say you have a giant instruction manual on how to build a car. Well the manual is made up of very specific instructions like, what materials are needed, how to make the bolts, and all the way to what color to paint the car. Let’s say that in this manual you read, “Use the metal titanium to make the bolts.” You can think of that specific instruction as a gene.

Here is what it looks like inside the body.

Each cell in our body, typically, contains 23 pairs of chromosomes. We get 23 from mom, and 23 from dad, for a total of 46. Within these chromosomes are long strands of DNA. Well, remember DNA is made of 4 different nucleotides all paired together. The way in which they are sequenced is very important. Their specific sequencing tell our bodies what specific type of protein to make.

Let’s think back on our example of the giant instruction manual telling us how to build a car. Well, each set of instructions within that manual instruct us to do something very important and specific. The way that each set of instructions are written dictates how the car is built, assuming we are directly following the instructions. The words that the manual creator uses, guide us and tell us exactly how to perform the work that needs to be done. Well, the same is true for our bodies. Our bodies are building proteins based on, exactly, how it reads the sequencing of nucleotides.

In an instruction manual on how to build a car, you will see sentences that express a complete thought, and when you zoom further out you will see paragraphs that express a complete instruction for a specific car part. Well, similarly, the entirety of our bodies DNA represent our bodies entire instruction manual. It’s within these long strands of DNA, where we can find our specific paragraphs (or a specific segment of DNA), that tell us exactly how to build a specific part (or in our case protein) that make up the whole body. Well, that specific segment that tells us what specific protein to make is called a gene.

So, now that you have a fundamental understanding of what a gene is, and what it does, let’s look at alleles.

You may hear genes and alleles get talked about synonymously, or at the very least when one is brought up then the other is too. So, what’s going on here? What is an allele?

An allele is a gene. However, here is how they are distinguished:

Remember how we talked about how almost all of the cells inside of our bodies contain 23 pairs of chromosomes? 23 from mom, and 23 from dad. Well, mom and dad are not the same. They do not have the exact same DNA sequencing. They certainly have a lot of the same DNA sequencing, but it is not all the same. So, all of their genes that their offspring will inherit (or segments of DNA sequence) that are identical are called genes. The genes that you inherit that could potentially be different are referred to as alleles. An allele is a kind of gene that codes for observable traits, also known as phenotypes. A phenotype could be eye color, blood type, and so on. For example: you could inherit a gene (or allele) from dad that codes for the blood type A. Type A, and Type B alleles are always dominant alleles. So, since you inherited blood type A from dad, you are guaranteed to have a blood type with type A in it. Let’s say, you also inherit type A from mom. You are going to have blood type A. So, does this mean that it is not an allele, because both of the genes inherited from mom and dad are identical? No, because an allele just refers to genes that have the potential to be different, which are all phenotypes. So, it’s always an allele if it is a gene that codes for a phenotype.

We just looked at an example where a child inherited the same dominant blood type from each parent, but let’s say that the child inherits a different blood type. Let’s say that dad gave the allele for type A, and mom gave the allele for type B. Well, remember, type B is always dominant as well. So, in this case the child would have blood type AB. Blood type O is always a recessive allele. So, in order for a child to have blood type O, it would need to inherit the allele for blood type O from not just one parent, but from each parent. I think you guys get the point. Pretty cool stuff, right?

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See you guys next time!