Inheritance and Mutations
(Published in the newspaper Amigoe on the 3rd of December 2025)
Mutations are changes in your DNA. When we think of mutations, we often think of diseases. But most mutations don’t cause any problems. You won’t even notice them. And sometimes, mutations can even be helpful! This new series is all about these beneficial mutations in humans.
How does inheritance work?
DNA is found in every cell. It’s your genetic material. The entire genetic material of a human being is called the genome. Think of DNA as a recipe book for your body. This book is divided into pieces called genes. Each gene tells how one small trait is made (like your eye color or an enzyme). You’ll get two copies of this book. One copy comes from your mom and one from your dad. That’s why kids look like their parents. They’re a mix of both recipe books.
Impression of the human DNA
Genes and their versions
Genes are like instructions in our DNA that tell our bodies how to grow and work. Each gene can have different versions, which are like different instructions. For instance, the gene for eye color has two versions: brown and blue. The brown version is called “B,” and the blue version is called “b.”
Here’s the thing: uppercase letters like “B” represent dominant genes, while lowercase letters like “b” represent recessive genes. In the example of eye color, the brown version (B) is dominant, and the blue version (b) is recessive.
How many different combinations are there?
Think of each person as a mix of their dad’s and mom’s recipe books. That means they have two genes for every trait. So, for a certain trait, one gene comes from their dad and one from their mom. In every cell in your body, you have two copies of each gene for a trait like eye color.
Since you have two copies of each gene, there are lots of ways they can mix. Let’s say you’re thinking about eye color. You have a few options. One possibility is that you got the brown eye gene (B) from one parent and the brown eye gene (B) from the other parent. If that’s the case, you’ll have two copies of the brown eye gene (BB), and your eyes will be brown.
The second possibility is that you have received the B (brown eyes) from one parent and the b (blue eyes) from the other parent. For eye color, you have the combination “Bb”. Because the gene for brown eyes (B) is stronger than the gene for blue eyes (b), you have brown eyes. However, you’re a “carrier” of the gene for blue eyes. It doesn’t matter which parent gave you the B (brown eyes) or the b (blue eyes). The result is the same, namely “Bb” or “bB”.
The third possibility is that you have received the b (blue eyes) from one parent and the b (blue eyes) from the other parent. For eye color, you have the combination “bb”. You’ll then have blue eyes.
Sexual inheritance
You know how in all cells, we have genes that double? Well, if the father and mother have all the genes twice, then the children should have all the genes four times, right? But nature’s got a clever trick up its sleeve! The sperm cells and egg cells are the only cells that have only one gene for each trait. When the sperm cell and egg cell combine, the fertilized egg cell has two genes for the same characteristic. Problem solved!
Here’s how you can organize this information in a schedule. The genes of the sperm and egg cells from the parents are located on the outside of the diagram. For instance, the sperm cells on the left and the egg cells above or vice versa are also valid options. In the boxes, you’ll find the children with combinations of one gene from a sperm cell and one gene from an egg cell. This diagram presents four possible combinations for the children: “BB”, “Bb”, “bB”, and “bb”. Only the combination “bb” results in blue eyes. This demonstrates that in this example, brown eyes occur 75% and blue eyes 25% in the children.
Adapting to changing circumstances
Why is it so crucial to mix the genes? Imagine if this didn’t happen, like with cloning. With cloning, you only have one parent, and all the children are exactly like that parent. This can lead to some serious issues. For instance, if the parent is prone to a disease, then all the children will be too. A pathogen only needs to find one weak spot to wipe out the entire clone population. This happened, for example, with the Irish potato blight (Phytophthora infestans) in the 1840s and 1850s. The entire potato harvest in Ireland was destroyed. But with sexual inheritance, you have two parents, which means the genes are mixed and the children are different (except for identical twins). Because of the genetic diversity that then arises, the chance that a pathogen, for example, can affect the entire population is much lower.
What is a mutation?
A mutation is like a tiny error in the DNA recipe book. Sometimes, it doesn’t change anything, but other times, it can change an ingredient (like a protein) and affect our bodies. Mutations also make our genes more diverse, which helps us adapt to changing conditions and evolve over time.
Mutation
Where do mutations come from?
Mutations happen during cell division, especially when egg or sperm cells are made. Sometimes, tiny mistakes can occur when copying genetic material. Chemicals, radiation, or certain viruses can damage DNA. Many mutations happen without a clear cause.
When do mutations get passed on?
Not all mutations are passed on to our kids. Only changes in the germ cells, like egg or sperm cells, can be passed down. We call this hereditary info. Mutations that happen later in life, like in a skin cell, are called somatic mutations. These can affect the person, like causing a disease, but they’re not passed on to the next generation. Only mutations in egg or sperm cells can end up in our kids.
The influence of mutations
Mutations can have different effects. Sometimes, they don’t change anything at all. Other times, you can see them, but they’re not good or bad. Sometimes, they’re bad and can cause diseases or make you more likely to get sick. But sometimes, they’re good and help species adapt to their environment. This is called evolution, and these small benefits help future generations survive. This series is all about these advantageous mutations.
In this article, we discovered how genes are passed from parents to kids. Sometimes, tiny mistakes happen during this process, which we call mutations. Most of the time, these mutations don’t affect anything, but occasionally they can be harmful. But guess what? There are also mutations that are actually good for us! They help us adapt better to our environment.
Join us on an exciting journey into the world of human evolution! We’ll explore how tiny changes in our DNA, called advantageous mutations, have helped us adapt to various environments. In this series, we’ll uncover how pale skin evolved in areas with less sunlight, how certain mutations protect us from diseases like malaria and HIV, and how others enable us to digest milk or use oxygen more efficiently. Buckle up and get ready for an amazing adventure!
1. Inheritance and Mutations