What are the chances?

How genes control who we are

Genes are really cool, there is no doubt about it. But what do they do exactly?

Think of genes as little instruction manuals that help tell different parts of your body what to do. Genes are made up of our DNA and can be translated into protein that perform specific tasks that relates to a person’s physical traits.

What does our genes contain?


Since DNA is made of 4 types of chemicals A, C, T and G (Adenine, Thymine, Cytosine and Guanine) each gene is made up of a sequence of these chemicals. With each code something different is triggered.

How do we get our genes?

Genes are inherited. With 50% of our genetic material coming from each parent, we have an equal part from both mother and father.

If genetic material is equal why do I look more like one parent?

photo of woman's face reflection

While we inherit our DNA equally from both parents, not all genes are turned on, or in some instances suppressed. Since we DNA is built up of pairs of chromosomes, we receive 1 chromosome from each parent to give us a full set of genetic material. However, within these chromosomes are the alleles (a.k.a genes) that determine our traits.

As chromosomes work in pairs, the combination of alleles from each parent that triggers the same trait work together. The most common explanation of this is by showing how a child can be born with blue eyes even if their parents have brown eyes.

Brown eyes are caused by a dominant allele (let’s call this B) whereas blue eyes are caused by a recessive allele (let’s call this b). For brown eyes to occur, the genetic code must be BBor Bb.For blue eyes to occur, the genetic code can only be bb.

Parents pass one half of their chromosomes to their offspring to create a pair of chromosomes. Meaning two alleles, one from each parent are given. Now for a child with blue eyes to have brown eyed parents, both parents must carry the recessive blue-eye gene. This means that there is a 25% chance of them producing a blue-eyed child.

As you can see by the table below:

How blue eyes can be expressed

This gene expression can explain why traits may ‘skip’ a generation, the fact they haven’t technically skipped a generation, but rather they have been suppressed for the generation before.

This can also account for why you may look more like on parents than the other; it would be due to the fact they have more dominant genes. In principle darker genes are more dominant which is why if you have one parent for example who has blonde hair and blue eyes, and the other who has black hair and brown eyes, the chances of receiving the fairer traits are much slimmer, this because two copies of this allele is required whereas the darker gene is likely to only need one copy to be dominant.

Images courtesy of Unsplash.