Everything you need to know about Heterozygous and Hypomelanistic

What do hypo and het mean in reptiles? Have you ever heard the terms: heterozygous or hypomelanistic?

If you’ve been diving into the reptile community, chances are you’ve come across phrases like heterozygous, hypomelanistic, and even homozygous. If you’re someone who is a bit unsure as to what these words mean exactly, don’t panic, because you’re in the right place. We have the information that you need, even if you want to try your hand at breeding.

That’s why, today, we’ll be taking a look at what heterozygous and hypomelanistic mean, and where het and hypo came from. Once we really get into things, there will be some science terms (mostly genetics), so just be sure to bring your thinking cap with you on this one. This information is absolutely crucial if you’ll be thinking about breeding in the future.

Great Basin gopher snake
Gopher snake het for albino.

We’ll be breaking everything down into easy-to-sections for you, so if you want to skip around, we won’t stop you. Now, with that being said, we definitely recommend that you pay close attention to each and every section. This is due to the fact that these terms get mixed up quite easily, so we just want to make sure you’re well informed.

The sections we have for you today are as follows:

  • The basics (some key definitions before we get started)
  • Heterozygous (het)
  • Hypomelanistic (hypo)
  • A brief recap

Now that you know about what we’ll be going over, let’s take a look at what each term means.

Get ready for a quick genetics lesson, but don’t worry, we’ll make this as painless as possible.

The basics

Before we dive into heterozygous and hypomelanistic, we need to take a look at the basics first. This is due to the fact that both het and hypo are based on genetics, so we’ll need to show you exactly what that means first. Now, before you start to panic, there is no need to worry. We’ll make sure that we break this down as simply as possible.


The first thing we need to explain is DNA. Many of you are probably familiar with what DNA is, but in reptiles, DNA is where hypo and het stem from. This is due to the fact that DNA impacts the genetic code of everything, in this case, reptiles, which will then play a role in their genetic composition. This genetic composition is important because if you know and understand the traits of a particular reptile, you’ll be able to predict the traits of its offspring.

Here are some common things to look out for:

  • Somatic cells carry all of an animal’s genes, but that doesn’t mean all of those genes will be expressed
  • Gametes are cells that have the DNA of each parent (one chromosome from each parent)
  • Mutations, or morphs in the reptile world, occur when certain genetic material becomes mutated (a great example is the albino trait)
  • The reptile’s genotype is the array of genes that can be passed down to offspring
  • A reptile’s phenotype is a set of physical traits present within the reptile
  • Recessive genes require two of the same gene to appear in an offspring (not always get)
  • Dominant genes only require one gene to occur in an offspring, and will always make it into the phenotype
  • Alleles refer to alternative forms of a gene that tend to be caused by a mutation

Now that we have a brief look at some of these concepts, we’ll take a deeper look to explain some of these ideas.


As we’ve mentioned above, the genotype of an animal is the genetic makeup of that animal. The genotype is unique because it encompasses all of the DNA presents in a given reptile. Now, while it may be a good way to identify possible genes, the genotype is not always reflected within a reptile’s physical appearance. Therefore, when working solely off of genotypes, it’s crucial to know whether or not traits are dominant or recessive.


The phenotype of a reptile is comprised of the physical traits. While it may be influenced by the genotype, not everything from the genotype can make its way into the phenotype. If you notice that an animal has a certain unique skin pigmentation (Albino), this is due to the fact that animals having the albino gene within its phenotype. Now, the beauty of phenotypes is that they’re a bit more predictable. This is due to the fact that you can see the gene you desire, and pair up the reptile with another reptile of that same phenotype.


A dominant trait is a trait that will always be passed down to an offspring. This means that if a reptile has a dominant gene, regardless of if it shows in the phenotype, it will end up in the offspring. Also, a dominant gene does not require more than one parent to carry the gene. Therefore, if you have a reptile with a dominant trait, you can comfortably breed that reptile with other reptiles that may lack the trait.


Finally, the last traits we want to get into are recessive ones. Unlike dominant traits, a recessive trait is one that will require a little bit of extra effort to be passed down through the gene pool. This is due to the fact that recessive traits will require two of the same gene.

We know that we may sound a bit repetitive, and took a small leap into genetics, but this is some important information to understand before we get into the factors that play into heterozygous and hypomelanistic.


Now that you know what you’re looking at, we’ll start to breakdown the whole heterozygous concept. We’ll try and keep things brief, but you’ll definitely want to consider paying very close attention to this section. Let’s take a look.

What heterozygous (het) means in reptiles

Heterozygous is actually quite simple once you dive beneath the surface. This is due to the fact that heterozygous reptiles will be carrying two different alleles of a gene. These traits can be either dominant or recessive, but all you need to know for heterozygous is that the reptile has two different alleles present.

What about homozygous?

Now that we’ve touched on heterozygous, you’ll probably want to know what homozygous is. This is actually quite simple, and while het maybe two different alleles, homozygous reptiles will have two of the same alleles. So to make this simple, think of homozygous as the exact opposite of heterozygous.

Keep in mind that traits in both homozygous and heterozygous reptiles can be dominant or recessive.


Now that you know how heterozygous works, let’s take a look at how hypomelanistic works. This is the last bit of genetics we’ll throw your way, so you’ll be pleased to hear that this is the final section in that sense. Now, with that being said, let’s dive right in and take a look.

What does hypomelanistic (hypo) mean in reptiles?

Hypomelanistic means that there is a lack of pigmentation within a reptile species (or species in general) pigmentation is color within the skin, but with reptiles, this can even be in patterns. Therefore, if you’re working with an albino reptile, the albino trait would be considered hypomelanistic. This is due to the fact that albino skin essentially has little to no extra pigmentation.

When it comes to understanding hypomelanistic reptiles, one thing to keep in mind is that this is referring to a phenotype that lacks pigmentation. Also, the traits can be both dominant and recessive.

hypomelanistic corn snake
Hypo (hypomelanistic) corn snake


The tricky part about all of this is that each trait will fall into either a dominant or recessive category. This means, that if you’ll be breeding these mutilations, you’ll need to reference which traits you’re looking into. So in this section, we’ll address what this all looks like using the albino trait as an example. Let’s take a look.

Hypomelanistic breeding

Hypomelanistic is a bit different. This is due to the fact that this condition is related to a lack of pigmentation in certain reptiles. Breeding these species can be a bit more difficult, but if you manage to discover whether traits are dominant or recessive, you should be able to proceed as planned.

Heterozygous breeding

If you’ll be breeding traits that are recessive, like the albino mutation, sometimes a reptile may actually appear to be normal. If this is the case, this is a pretty good indication that the reptile is heterozygous. For a reptile of this genotype to produce the mutation in their phenotype, you would need to breed two reptiles with the same albino trait (alleles).

Hopefully, this section gave you some useful insight into how this whole breeding process will work. It can be simple once you understand the factors at play, but you’ll need to figure out which traits you’re working with in order to obtain accurate results.

We know that we went over a whole lot of genetics today, and we understand that it can get a bit confusing at times. Therefore, please feel free to refer back to this post as a guide if you need to. We just want to make sure that you’re well informed, and if you’ll be breeding a hypo or het gene, informed is something you’ll need to be.

Once you understand the basics, you can begin to take a deeper look into hypomelanistic and heterozygous. We just want to make sure that you understand the basics, and if you made it this far you certainly do.

Now that you know the facts, do you feel a bit more comfortable?

Please leave your comments in the section below! 

Everything you need to know about Heterozygous and Hypomelanistic

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