PTC Genetics of Bitter Taste

Have you ever been puzzled about why some people can happily munch on broccoli, while others wrinkle their noses at it? Or have you noticed how some of us can’t stand even a sip of coffee, but for others, it’s like a daily fuel? This mystery might just be hidden in our genes, specifically those that shape how we taste things.

One key player in this genetic taste test is the gene linked to PTC, a substance that’s become a sort of benchmark in understanding our taste buds.

In this article, we will go into the complexities of the PTC gene, TAS2R38, and discover how it influences not just your reaction to PTC, but to a range of bitter flavors.

We will discuss the genetics of taste, the evolutionary significance of bitter taste perception, and the global variations in PTC sensitivity.

Quick Note:

In a hurry? Here’s the essence: Our taste preferences, particularly for bitter flavors, may be rooted in our genes, particularly the PTC gene, TAS2R38. This gene influences how we perceive a range of bitter tastes, not just the synthetic substance PTC.

Variations in the TAS2R38 gene, determined by specific SNPs, result in differing sensitivities to bitter flavors. These genetic differences along with some other genes are responsible for why some of us find certain foods like broccoli or spices delightful, while others find them unpalatable.

Additionally, our ability to taste bitter flavors plays a crucial evolutionary role, helping our ancestors avoid toxic substances. Today, this genetic trait can impact our dietary choices, potentially influencing health outcomes like obesity, diabetes, and heart disease, though the research is still evolving.

For a deeper exploration and their broader implications, keep reading!

Here is a simplified PTC predictor to see the chance of your child PTC sensitivity.

What is PTC and Its History

PTC, or phenylthiocarbamide, might sound like a complex chemical, but it’s actually just a synthetic substance, found not in nature but in labs.

Its story began back in 1931 when chemist Arthur Fox accidentally discovered that people reacted differently to its bitter taste.

Some found it intensely bitter, others couldn’t taste it at all. Fox’s simple experiments with friends and family uncovered something intriguing: the ability to taste PTC or not seemed to run in families.

This discovery turned PTC into a star of sorts in the world of genetics, especially in studying how we perceive taste.

Understanding Bitter Taste Genetics

Let’s find out how PTC gene influences our perception of bitter tastes.

What is the PTC Gene?

PTC stands for phenylthiocarbamide, a chemical that helps scientists study how we taste bitter flavors.

Our ability to taste PTC (or find it tasteless) is “largely” due to a gene called TAS2R38.

This gene makes a protein that acts like a bitter taste sensor in our mouth. When it comes across bitter substances like PTC, it sends a signal to our brain, and we perceive bitterness.

The PTC Gene Variations

Not everyone has the same version of the TAS2R38 gene. There are different versions, or alleles, of this gene, and they change how the protein works.

These differences are what make some of us find PTC very bitter, while others can’t taste it at all.

To get even more detailed, scientists look at something called SNPs (single nucleotide polymorphisms). These are tiny changes in the DNA of the TAS2R38 gene.

Three main SNPs affect how we taste PTC: rs713598, rs1726866, and rs10246939. These changes alter the protein’s structure and, consequently, how we taste bitterness.

The Different Types of PTC Tasters

Based on these SNPs, there are six common types, or haplotypes, of the TAS2R38 gene: PAV, AVI, AAV, AI, PVI, and PVV.

Each of us gets two copies of the TAS2R38 gene, one from each parent, and the combination determines our sensitivity to bitter tastes like PTC.

• High Sensitivity (PAV/PAV): People with two copies of the PAV haplotype usually find PTC very bitter.
• Low Sensitivity (AVI/AVI): Those with two copies of the AVI haplotype might not taste PTC much, if at all.
• Medium Sensitivity (PAV/AVI): If you have one of each, PTC might taste somewhat bitter.

The other haplotypes like AAV and AI have different levels of sensitivity, and some, like PVI and PVV, show varied effects on taste perception.

Is PTC Tasting Dominant or Recessive?

In genetics, we often talk about traits being dominant or recessive.

Generally, the ability to taste PTC is considered dominant. This means if you get the PTC taster gene from even one parent, you might be a taster.

However, the full story is more complex, with various degrees of tasting ability based on the exact combination of haplotypes you inherit.

Is PTC Tasting a Simple Case of Inheritance?

Originally, scientists thought PTC tasting followed a simple pattern of inheritance. They believed it was all about dominant and recessive alleles, like in Mendelian genetics.

In this view, if you got the dominant allele (let’s call it T) from either of your parents, you’d be able to taste PTC.

If you got two recessive alleles (t) – one from each parent – you wouldn’t taste it. This idea came from early studies using PTC paper to test people’s taste sensitivity.

But, it turns out, PTC tasting isn’t that simple.

The story gets a bit more complicated when we look at how intensely people taste PTC. Some people might find PTC extremely bitter, others only a little bitter.

This range of sensitivity doesn’t really fit with the simple dominant-recessive idea.

Incomplete Dominance

Another way to think about PTC tasting is through incomplete dominance.

This idea suggests that if you have two copies of the ‘tasting’ allele (TT), you’re very sensitive to PTC. If you have one ‘tasting’ allele and one ‘non-tasting’ allele (Tt), you’re moderately sensitive.

And if you have two ‘non-tasting’ alleles (tt), you won’t taste PTC at all.

This model helps explain why there’s such a variety in how bitter PTC tastes to different people.

But, even this model has its limits. It doesn’t explain why people with the same genetic makeup (like TT, Tt, or tt) can still experience PTC differently.

Multiple genes

This hints at something more complex going on – maybe other genes or environmental factors also play a role in how we perceive PTC.

Research has indicated that other genes may also contribute to the ability to taste PTC.

These genes could be involved in various aspects of taste perception, such as the development of taste buds or the signaling pathways that transmit taste information to the brain.

The Big Picture of PTC Tasting

What all this shows us is that tasting PTC (and other bitter substances) is influenced by multiple genes and a mix of factors – not just our genetics, but also things like our physiology, psychology, and even culture.

There’s no one-size-fits-all explanation for why we taste things the way we do. It’s a complex interplay of many elements that make each person’s experience of taste unique.

A dry mouth could hinder your ability to detect the bitterness of PTC effectively. Moreover, the types of foods or beverages you’ve consumed prior to a PTC taste test can influence your ability to perceive its taste.

It’s also notable that a person’s sensitivity to PTC isn’t constant and can vary over time. There are instances where individuals might notice a variation in their PTC tasting ability, being able to taste it on certain days but not on others.

The Role of Bitter Taste in Evolution

Bitter taste isn’t just about what we like or dislike in our food. It’s much more important—it’s about survival.

Our ability to detect bitter tastes, like what we experience with PTC paper, is a key part of our body’s defense system.

It helps us avoid eating harmful things, especially toxins in plants.

How Bitter Taste Helped Our Ancestors

Imagine our ancestors, navigating a world full of unknown plants. Being able to taste bitterness—a sign of potential poison—was crucial.

This is where our bitter taste genes, including the PTC gene, come into play. They gave our ancestors a survival edge, helping them avoid dangerous plants.

Bitter Taste Genes Across Species

Interestingly, not all animals have the same number of bitter taste genes. Humans have around 25 of these genes, but our primate relatives like chimpanzees and gorillas have fewer.

This difference suggests that our ability to taste bitterness, including tasting PTC, has evolved differently based on our diets and environments.

Not All Bitter Tastes Are Bad

Some bitter substances, like caffeine and nicotine, can be harmful in large amounts but also have benefits.

Others, like quinine and salicin, are actually medicinal. So, being sensitive to these tastes can influence our health and behavior in various ways.

PTC Tasting in Humans and Primates

When we compare PTC tasting in humans to other primates, we see some fascinating differences. Chimpanzees and gorillas, who eat mostly plants, are more sensitive to PTC than omnivorous humans. This could reflect their need to be more cautious about bitter plants.

On the other hand, some human groups like the Hadza of Tanzania, despite eating a lot of bitter plants, are less sensitive to PTC. This could be a genetic adaptation to their specific diet and environment.

In summary, the ability to taste bitter substances, governed by our bitterness tasting genetics, including the PTC gene, plays a crucial role in our survival. It’s a fascinating example of how our senses have evolved not just for pleasure, but for protection.

How PTC Tasting Can Affects Our Health

Understanding your PTC gene type, which is linked to the ability to taste PTC (a bitter compound), might have significant health implications. This genetic trait can influence your dietary preferences, potentially impacting your health in various ways.

PTC Tasting and Health Aspects

1. Obesity: PTC tasters might avoid bitter foods, like certain vegetables, opting for sweeter or fattier foods instead. This preference could affect weight, though research findings are mixed, with some studies suggesting a link between PTC tasting and higher BMI, and others showing no clear connection.
2. Diabetes: The hypothesis here is that PTC tasters may have a reduced sensitivity to sweetness, potentially impacting their sugar metabolism and insulin regulation. However, studies on the relationship between PTC tasting and diabetes risk show inconsistent results.
3. Heart Disease: There’s a theory that PTC tasters might consume fewer bitter, heart-healthy foods such as green tea or cocoa. Non-tasters may consume more of these beneficial foods. However, there’s limited research to fully support this idea.
4. Thyroid Function: PTC and similar substances can influence thyroid function, important for metabolism. There’s a possibility that PTC tasters might have an increased risk of thyroid issues, especially in areas with iodine deficiency, but the evidence is not conclusive.
5. Cancer Risk: Some researchers believe PTC tasters might have a lower intake of certain vegetables that could protect against cancer, while non-tasters might have a higher intake of these beneficial foods. Again, research results are varied, with no clear consensus.

In short, while there are theories connecting PTC tasting to various health conditions, the research is still evolving. More studies are needed to fully understand how this aspect of taste perception relates to health.

PTC Sensitivity Across Populations

The TAS2R38 gene has different versions, known as variants or haplotypes, and these vary widely across the world.

For instance, in some Native American and African populations, less than 10% of people can taste PTC, while in some Asian and European groups, more than 90% are PTC tasters.

These variations can tell us a lot about human migrations, how different groups have mixed over time, and how we’ve adapted to our environments.

Final Words On PTC Genetics

Taste perception is a rich and intricate field that blends genetics, environment, and culture. Our diverse reactions to tastes, especially bitter ones like PTC, stem from variations in taste genes such as the PTC gene.

This genetic diversity contributes to different food preferences and dietary behaviors across populations, influencing health and nutrition.

Let us know in the comments below if you are a taster or non-taster.

References:

• Association Between Bitter Taste Receptor Phenotype and Clinical Outcomes
• Genetic, Functional, and Phenotypic Diversity in TAS2R38-Mediated Bitter Taste Perception
• Development of a molecular method for the rapid screening and differentiation of TAS2R38 tasters and non-tasters
• A Taste of Genetics – PTC Taster – Biology LibreTexts
• TAS2R38 Single Nucleotide Polymorphisms Are Associated with Human Taste Perception
• TAS2R38 and Its Influence on Smoking Behavior and Glucose Homeostasis
• Natural Selection at Work in Genetic Variation to Taste or Not to Taste Bitter Compound