Introduction to Snake Genetics
A Study of Hognose Snake Morphology
Learning Module
- Creator(s):
This course is a primer on hognose snake genetics in regards to the different colors and patterns found in the species. The course will explore what a gene is, how they are passed on from parents to offspring, the different types of genes, the different genetically linked traits of hognose snakes, and finally how to determine what genes may be present in offspring by analyzing the genetics of the parents. The course will utilize multiple modes of instruction and apply the elements of New Learning (Cope & Kalantzis, 2013) to the study of snake genetics online. Learners will be required to apply their newly gained knowledge through comments and learning log updates wherein they will explore thought experiments and solve problems using the information provided in the module. At the culmination of the course, the learners will be required to use the knowledge gained throughout the course to present a final project where they will create a breeding plan for a theoretical set of hognose snakes in order to reach a specific morphological goal. Their breeding plans will be reviewed by their peers in the course and feedback will be given to enhance the breeding plan.
The course as described is newly designed as of May 2021 by the author and is intended for those with little current knowledge of genetics or hognose snake morphs. Though designed as a primer for those possibly interested in snake breeding, with a little editing the course may be suitable for an introductory genetics portion of a larger biology course.
In this course, we will be exploring the genes and their effects on heredity in snakes. We will explore what genes are and how they are passed from parents to offspring. We will then discuss the different kinds of genes as well as some examples of those types of genes in relation to the color and pattern of hognose snakes.
By the end of this course, the learner will be able to:
This course is designed to take seven weeks to complete. However, if you find yourself wanting to skip ahead or find yourself wanting more time for each module, feel free to let the administrator of the course know and we will accomodate you. Each week will consist of a discussion session where we will discuss the week's content and the implications of the content in the real world of breeding snakes. We will also be using weekly "Learning Logs" to draw parallels between the coursework and more familiar genetic heredity found in humans.
Finally, we will finish the course with a final project in the form of a breeding plan. You will take a theoretical set of hognose snakes and design a breeding plan to get to a specific genetic result in the resulting offspring. These breeding plans will then be reviewed by your peers for their efficacy and efficiency, after which you will have the opportunity to revise your plan before submission.
Prior to the next class, please take this quick survey, to allow for the instructor to better adjust the course content to fit the needs of the class:
There is a pre-course survey which is linked here:
This is Google form survey which will allow for updates and revisions if necessary or desirable in the future. The questions in the survey are designed to provide you with a better idea of the prior knowledge of genetics the learners may have. An example of one of the questions is below:
Incomplete dominant genes are only fully expressed when there are two copies of the gene.
In this case, if the learners choose “Don’t Know” then we can assume that they have virtually no experience with genetics. If they choose “False” then they probably know something about genetics, as dominant genes only need one copy to be fully expressed, while incomplete dominant genes need two copies. These kinds of questions should prove useful to determine how the course should proceed. As the course currently is designed for learners with little to no experience with genetics, if the majority of the learners have more familiarity with genetics, then the course may need to be more technical in nature.
Some of the questions posed in the pre-course survey are more straightforward in nature, such as those asking what age group the learners fall into. Use the results of the survey to not only determine how technical or general the terminology in the course should be, but also what references may be used to greatest effect when speaking with the participants.
In the following course, we will be discussing the basics of Mendelian Genetics and how they apply to Hognose Snake breeding in reference to the more commonly seen morphs. The topics are as follows:
The modules are partitioned in this manner to facilitate a building of knowledge. As such, each module of the course builds on the knowledge of the previous module. As the facilitator, be very certain to engage the participants as much as possible in order to ensure they understand the material from the previous module before moving on to the next.
With this is mind, the learning objectives for the course are as follows:
By the end of this course, the learner will be able to:
Provided throughout the modules are discussion questions and comments, as well as independent “Learning Log” entries. Each prompt is designed to not only determine the knowledge acquisition of the learner, but also to draw parallels to their personal lives as well as foster a greater sense of self-direction in their learning. Many of the prompts have a problem-based element to them, where the participant is required to do independent research to answer a specific question. You are encouraged to answer questions regarding these prompts, but to answer in a way which guides the learner instead of simply giving him or her the answer. The end goal is to foster a capability of independently planning out genetic pairings and understanding the possible outcomes of those pairings beyond the end of the course.
Before we talk about how certain genes present in snakes, we need to learn about genes themselves, as well as what happens when animals mate at a cellular level. To begin, let's talk about what genes are.
In all animal, plant, and fungi cells is a central envelope which holds DNA. DNA is the code which tells our bodies what to do and how to look. Portions of DNA can be "decoded" to tell the body of the animal, plant, or fungus to produce specific proteins which do specific tasks. Each of these portions of DNA is called a "gene". For example, a portion of the DNA in our cells tells the body to make a protein which in turn makes our eyes the color they are. If this is confusing, the video below may help to make things clearer:
(Stated Clearly, 2012)
Now that we understand what a gene is, we need to dicuss how those genes are passed on to our offspring. In each cell, there are two copies of each gene. When an animal like a snake mates, some of its cells split its DNA in two to create what is called a "gamete". Gametes are the sprem in males and the eggs in females. Because of this splitting process, called meiosis, the snake will only pass on one copy of the gene in question. When a male and a female gamete meet and fuse to form a new cell, they complete the pair and that cell will then grow into a baby snake. So, in the end, the baby snake has one copy of the gene from its father, and one copy of the gene from its mother. The video below goes over the process of meiosis in a little more depth:
(CrashCourse, 2012)
In the following modules the definition of genes and the process of meiosis will play a big role, so be sure you understand!
Comment: Think of a trait that you have that can be explained by the process of meiosis. Why do you think that trait is an example? Example: My hair is curly. My mother has straight hair, but my father has curly hair. The gene for curly hair must have gotten passed on to me by my father!
Learning Log: Blood type is a perfect example in humans of meiosis at work. We will be using human blood types as an example for some of our future modules. Write a learning log update where you look up and catalog the human blood types. How do you think that the genes for blood types are passed on?
Discussion comment: The comment prompt for this week is designed to help the learners think critically about genetic traits as they relate to their own life and experiences. Depending on the experience of the learners, they may struggle with the concept of meiosis. Be prepared to talk learners through the concepts again and provide more examples as well as ask probing questions to see why they think the traits they used are an example of meiosis. If the learners struggle with these concepts, they will struggle with the rest of the course so understanding is paramount.
Learning Log: Throughout the course, we will be looking at human blood types as a way to analyze the concepts of the module in question. This helps to bring the message into a more relatable scene and engage with the learners' prior experiences. Though the intent is to get the learners to look into human blood types themselves (and thus foster more self-directed and metacognitive learning), be prepared to answer questions about blood type genetics if learners get stuck.
Last module we dicussed genes and meiosis and their role in passing on traits from parents to offspring. Now we will delve into what that means for snake genetics, starting with dominant genes.
Dominant genes are genes which, as the name implies, are dominant to other genes. Dominant genes will be expressed no matter what other genes are paired up with them. In the case of hognose snakes, the most common dominant trait is the "wild type" or "normal" hognose snake, which can be seen below:
The dominant gene here gives the snake its rusty brown color and its busy, spotted pattern. No matter what other gene it is paired with, if there is a wild type color gene present, the snake will look rusty brown. If there is a wild type pattern gene present, the pattern will be busy and spotted.
An example in humans, which also shows an example of a co-dominant gene, is with blood type. Humans have three possible genes which dictate our blood type: A, B, and O. A and B are both co-dominant genes while O is a recessive gene (which we will cover in a later module). If you have one copy of an A gene and one copy of an O gene, you will have type A blood. However, blood type genes are co-dominant, which means that if there are two of the dominant genes, both will be expressed. If you have a copy of an A gene and a B gene, then you will have type AB blood. There are no known instances of co-dominant genes in hognose snakes.
Comment: What trait do you have that you think could be a dominant gene you got from one of your parents? Why do you think that that trait is dominant?
Learning Log: There is one other gene associated with human blood types that was not included in the example above. Do some research and write a learning log update on that other gene for blood type. Is the gene you found dominant? What does that mean in terms of what your blood type would be if it was present?
Comment: Once again, the discussion this week is designed to help the learners to connect the content of the module with their own lives and experience. Though dominant genes are generally well understood, be prepared to answer any questions necessary to distingusih we a dominant gene is.
Learning Log: The other blood type marker that is referenced here is the Rh+ or Rh- gene (e.g. A+ vs A- blood types). The Rh gene acts in a dominant manner. You either have the Rh+ gene or your don't. The goal is to get the learners to discover this, as well as how it works, by themseleves. Depending on the learners' capabilities in self-directed learning, this may take some persuasion and help. Be prepared to ask guiding questions if the learners have questions about what the exercise means or what they should be looking for.
In the last module we talked about dominant genes and how no matter what other genes are with them, they will be expressed. This module we will discuss a different kind of dominant gene: Incomplete Dominant.
Incomplete dominant genes are genes which are always expressed, but they need two copies in order to be fully expressed. One example in hognose snakes is the "Acrtic" coloration gene. Arctic changes the snake's color to have more stark contrast of whites with blacks, and makes outlines around the snake's spots. Below you can see two pictures of arctic hognose snakes. Can you tell which snake has only one copy of the acrtic gene and which has two copies?
If you said the first picture has two copies of the arctic gene while the second only has one copy, then you are correct! The snake in the second picture is much closer to the color of a wild type snake, but with some changes in the contrast of the lights and darks. Meanwhile, the first picture is a snake with almost a black and white look to it.
The second example of incomplete dominance in hognose snakes is the "Anaconda" gene. Unlike the arctic gene which effects the snake's color, the anaconda gene effects the snake's pattern. Essentially, the anaconda gene might better be described as a "patternless" gene, as with two copies of the gene, the spots completely disappear from the snake's pattern. Meanwhile, having only one copy of the anaconda gene means the snake's spots are merely less busy. Below you can see two pictures of hognose snakes, the first has only one copy of the anaconda gene, while the second has two copies.
In this case, the color of the snake has not changed, just the pattern. Next module we will discuss recessive genes and how they play into hognose snake colors!
Comment: When it comes to breeding snakes and figuring out what the patterns of the babies will be, why is it important to know whether the parents have one or two copies of the gene you're breeding for?
Learning Log: Again, let us consider blood type for this learning log. This time, write a log examining how you know that the A and B genes are not incomplete dominant genes, but are actually co-dominant genes.
Comment: This prompt is meant to reinforce the concept of meiosis, but it's also meant to help the learners distinguish between dominant and incomplete dominant. Also, the prompt is meant to lay the foundation of thought necessary for the recessive gene module next week. Be sure to ask probing questions of learners who don't seem to grasp the entirety of why it's important to know what genes are being passed on as this will factor into their understanding of future modules as well as their final project.
Learning Log: This prompt, as we've seen before, does involve some amount of self-directed learning. Though we have spoken briefly about co-dominant genes, this learning log is designed to get the learner to think about why co-dominant genes are not incomplete dominant and vice versa. Again, be prepared to ask guiding questions if the learner is confused.
In the past two modules, we have examined the way dominant, co-dominant, and incomplete dominant traits work with colors and patterns of hognose snakes. This module, we will be exploring the way recessive traits effect a snake's colors, as well as going through multiple color examples for recessive traits in hognose snakes.
Recessive genes are genes which get completely taken over if there is only one copy of the gene. The only way that recessive genes can be expressed is if there are two copies of the gene. In genetic terminology, if a snake has only one copy of a recessive gene, they are heterozygous, or "het" for that trait. If the snake has two copies of a recessive gene, then the snake is homozygous for the trait. If this is confusing, check out the video below talking about snake genetics using bull snakes as an example:
(Snake Discovery, 2017)
As it turns out, the majority of hognose snake color morphs are actually recessive traits! Albino, for example, is the most common. This gene stops the snake from making melanin, which takes away the blacks and browns in the snake's color and it looks yellow, red, and orange:
Conversely, the Axanthic morph reduces the expression of reds, browns, and yellows, causing the snake to be a grayscale color:
The Hypo coloration is also caused by a lack of melanin, just like Albino. However, the reduction in melanin is limited to only the black colors, so the reds, yellows, and browns are all expressed:
The Lavender gene is a strange one in that it actually makes the snake look purple, with darker purple eyes:
Likewise, the Pink Pastel gene actually makes the snake look bright pink!
The Leusistic gene causes the snake to not be able to produce any color pigments, resulting in a totally white snake:
The Sable gene, on the other hand, causes an excess of melanin to be produced, resulting in a snake with a very dark color:
There are more recessive color morphs for hognose snakes, but the ones listed here are the main colors you will see of hear about.
Comment: Post a comment answering this question: If I were to breed an albino female hognose to an axanthic male hognose, what kind of color morph would the babies be?
Learning Log: Once again go back to the human blood type example. Of the A, B, and O genes which determine blood type, one of them is recessive. Which one? How many different blood types can be found using that recessive gene?
Comment: The answer to this prompt is simply that the baby would look normal, but be "het" for albino and axanthic. Make absolutely certain that the learners understand that the baby of two parents with different recessive phenotypes would not show either of those traits outwardly.
Learning Log: The answer of which gene is recessive should be relatively easy for the learners to pinpoint at this point. However, it is important that they are able to recognize that someone with a blood type of A can have have one O type gene.
The previous modules have explored what a gene is, how it is passed on, what dominant, co-dominant, incomplete dominant, and recessive genes are, as well as some examples of different types of genes in hognose snakes. This module we will be discussing how we determine what genes are passed on and why.
To begin, watch the following two videos about dominant and recessive genes:
(2 Minute Classroom, 2017)
(2 Minute Classroom, 2017)
So, now we should better understand about dominant versus recessive genes and homozygous versus heterozygous gene pairs. We may remember that in Module 2, we talked about how only one copy of a gene is passed on from the parent to the offspring. So, with this in mind, watch the video below on genetic probabilities where he talks about how to determine how many offspring of various parentage will display recessive traits and how many will display dominant traits. Though the entire video is interesting, if you wish to only view the portion on probabilities, skip to 8:00.
(Professor Dave Explains, 2017)
Comment: Given what we just learned about genetic probabilities, post a comment where you give an example of a male and female hognose snake pair who would have a 50% chance of producing an offspring who displays a recessive trait.
Final Project!
Throughout this course we have explored the concepts of dominant, incomplete dominant, and recessive genes and how they can apply to hognose snake morphs. In this last module we explored ways to determine what kinds of genetics the offspring of two parents could have and the probabilities of each. Now, we will put this to the test. Your final project for this course is design your own breeding plan. The instructor will supply you with a theoretical group of hognose snakes, including their genetics. The instructor will also assign you a morph or combination of morphs to produce from this group of hognose snakes. Your task is to create a breeding plan which uses the least amount of generations to produce the desired genetic result. Along the way, be sure to calculate and take note of the percentage probabilities of producing the desired genetic combination! After you have completed the breeding plan, write a summary of it with an explaianation of why you chose what pairings you did throughout the plan. Upon submission, your breeding plan will be reviewed by your peers, who will provide feedback on your plan according to the attached rubric. After recieving your peer feedback, if necessary, you may revise your breeding plan before finally submitting it for instructor review.
Good luck designing your breeding plans, and have fun!
Comment: This may be a really difficult one for students to wrap their heads around. The only way to get a 50% chance is to have one parent who is homozygous recessive and one who is homozygous recessive. Again, be prepared to ask guiding questions if learners seem to be having some issue with the concepts.
Final Project:
For the final projects, you will provide the participants with a “breeding group” of adults from which they will make a breeding plan resulting in an offspring with specific genetics. Be sure to give each participant a different set of parents and / or a different end result. This will allow them to consult other members of the course for help if desired without simply getting the answer from someone else. Be sure to give them a breeding group which would require at least three generations to get to the desired genetic offspring. Remember, as this is a theoretical exercise and no snakes can be “proven”, make sure to provide visual recessive snakes as starters for the breeding group, not simply hets. An example is this:
Breeding Group:
Desired Offspring :
The above example should get the learner to the desired offspring in more than three generations. Final projects for the course should be written out in a thorough manner in consultation with the content of the course. The pairings, as well as the genes in play should be recorded. All of the pairings should be accompanied by probabilities for the offspring produced. A discussion of why the participant chose the pairing they did should accompany the breeding plan.
Throughout this course we have explored the concepts of dominant, incomplete dominant, and recessive genes and how they can apply to hognose snake morphs. In the last module we explored ways to determine what kinds of genetics the offspring of two parents could have and the probabilities of each. Now, let's see some of the possibilities of combining some of these genes!
Combinations of genes do exactly that: combine the effects of the genes in play. With many snakes, multi-gene combinations are given their own name. For examples, we will look at some of the more commonly found combinations involving the Albino gene. Possibly the most commonly seen is the combination of Axanthic and Albino genes, called a "Snow", which can be seen below. The Albino gene causes a lack of melanin production, while the Axanthic gene causes a lessening of the production of reds and yellows, resulting in an almost to fully white snake:
If we take it further and combine Axanthic, Albino, and one copy of the Anaconda gene, we get a "Yeti":
Finally, if there are two copies of the Anaconda gene, the morph is called a "Super Yeti"
We see this kind of renaming with a variety of gene combinations, like the "Toffeeglow", which is a combination of Albino and Toffeebelly genes:
Or the "Sunburst" and "Sunfire", both of which combine the Albino and Sable genes, with the latter adding in the Anaconda gene:
Finally, we see the "Coral" combination of morphs, which combine Albino and Lavender genes:
Comment: Find another combination of genes in hognose snakes that have a different name, let us know what it is and what genes are at play!
Learning Log: Take the gene combination that you used for your comment for this module. Starting with parents who show one of each trait, calculate the odds of creating the combination from those parents. For example, for a Snow hognose snake, I would start with one Albino and one Axanthic parent and follow the next two generations to get a Snow snake.
Final Project Peer Reviews: You have been assigned one of your peer's final projects to review. Use the rubric to give feedback to your peer about the breeding plan they submitted. Be supportive but honest. If they missed an element in their breeding plan, they may have only a partial picture of what it would take to breed with specific goals in mind.
As a reminder, the reviews should follow the following rubric for review criteria:
Comment: Some students may need some help in finding different gene combinations, be prepared to provide guidance as needed.
Learning Log: This exercise is intended to reinforce what is needed for the final project. This also has the secondary function of displaying examples of the odds calculations needed for the final project through a public post.
Final Project: Be prepared to help with participants' reviews of their peers. Some learners may need more specific directions or clarification of the rubric.
2 Minute Classroom. (Apr 25, 2017). Homozygous vs Heterozygous Alleles | Punnet Square Tips. [Video]. YouTube. https://www.youtube.com/watch?v=D8Nu3Aw6F2A
CrashCourse. (Apr 23, 2012). Meiosis: Where the Sex Starts - Crash Course Biology #13. [Video]. YouTube. https://www.youtube.com/watch?v=qCLmR9-YY7o
EctoTherm Empire. (n.d). Western Hognose Morphs. [Website]. https://www.ectothermempire.com/western-hognose-morphs.html#/
Professor Dave Explains. (Oct 3, 2017). Mendelian Genetics and Punnett Squares. [Video] YouTube. https://www.youtube.com/watch?v=3f_eisNPpnc
Snake Discovery. (Oct 31, 2017). An Intro to Snake Genetics! [Video]. YouTube. https://www.youtube.com/watch?v=Lcm13UG327U
Stated Clearly. (Nov 26, 2012). What is a gene? [Video] YouTube. https://www.youtube.com/watch?v=5MQdXjRPHmQ