Does DNA Decide If You Are Left Or Right-Handed?

Most of us are right or left-handed in that we predominantly use one hand consistently to complete key tasks like writing. But what role does genetics play in deciding if we are right or left-handed?

Research of the DNA of more than 1.7 million people was analysed by 23andme and the International Handedness Consortium. They discovered that rather than one gene being involved, 41 regions of the genome were associated with being left-handed and 7 were associated with being ambidextrous. So, the research suggests that genes play a role, but no single gene is the cause.

Hand Choice Develops In The Womb

Whether you are right or left-handed tends to show by the time you are starting to draw as a young child and hold pens and pencils. However, the signs of which hand you will favour can be there much earlier. In fact, research also suggests that we start to show this in the womb. In fact, research looked at individuals who sucked their thumb in the womb and then revisited them as young children. Of the 75 people in the study 60 who sucked their right thumb went on to be right-handed, 10 of the 15 who sucked their left thumb went on to be left-handed. So, this study found a strong correlation between thumb sucking choice and handedness, particularly so for right-handed foetuses.

Has This Always Been the Way?

It does seem as if we have always favoured right handedness as human beings. Researchers have looked at fossils to see which hand our ancestors favoured and it seems that the right handers have it. In fact, it’s one of the things that makes humans so unique, as no other primate has the kind of bias we show to the right hand.

What Causes Variation In Handedness?

So, we know that genetics does play the largest role, but other factors can be responsible for variation. We can for example be trained to use a different hand and the way we develop our motor skills when very young can also play a role in which hand we favour.

The Role Of Genes

People have tried for years to pinpoint which gene is responsible for deciding whether you are right or left-handed. But it is now understood to be more complicated than this. In fact, studies using Genome Wide Association Studies (GWAS)conclude that nearly all human traits are influenced by not one but hundreds or thousands of genetic variants. So, in reality lots of genes make small effects rather than one gene having one large effect. In fact, what used to be termed ‘junk DNA’ may in fact be more important than we thought.

Junk DNA

A quick explanation of junk DNA. The term junk DNA was first used back in the 1960’s. It refers to the parts of the DNA which are non-coding and in the past were therefore seen as somewhat useless. But what always troubled scientists is what the purpose of these bits of DNA were. As we now understand though the term junk is not very helpful. So called junk or non-protein coding DNA do perform key functions such as repairing DNA, aiding in fighting diseases and regulating DNA replication.

What About People Who Are Ambidextrous?

Research tells us that on average 88% of people are right-handed, 10% prefer to use their left hand and 2% say they can use both. This latter condition is known as being ambidextrous. It is accepted that understanding ambidexterity is very complicated with some scientists suggesting that what influences the direction of hand preference may be different from what influences the degree of hand preference. So, whilst we now have some understanding of the number of genes involved in deciding handedness more work is needed in understanding how genetic variants decide if someone is right, left or the more unusual ambidextrous.

Genome Wide Association Studies (GWAS)

GWAS have played a role in helping us to understand which genes are involved in left or right handedness. But what are GWAS? 

GWAS involves scientists looking at genomes to find common genetic variations associated with a particular characteristic What they are looking for is single nucleotide polymorphisms or SNP’s, these vary between individuals and can be associated with certain diseases.

In studies of this nature the genomes from two groups of people will be studied. The first group will have a disease or characteristic that is being studied, the second group will not have the disease or characteristic. Both will supply a DNA sample and their genome is then analysed looking at the SNP’s to see if any are more common in one group than the other. To put bluntly if certain SNP’s are more common in those people with a disease then it is safe to say they are associated with that disease.

Why Are Genome Wide Association Studies Important?

The results from GWAS are important as they can help us better understand how diseases develop and how they can be treated. Success stories to date have included the identification of the SNP’s associated with Type 2 Diabetes, Alzheimer’s, Parkinson’s and Crohns Disease. They have also helped us understand how some people respond to anti-depressants and also obesity.

The First Successful GWAS

2005 saw the first published GWAS which looked at people who suffered from a condition called AMD-age related macular degeneration which is a n eye condition which can lead to blindness. Two SNP’s were found in individuals with the disease compared to those without it. The study also suggested that controlling inflammation in the eye could be key to controlling the disease. This subsequently led to anti-inflammatory medications being used in an effort to help those with the disease.

How Could GWAS Help Us In The Future

It does take time for information to be taken from the GWAS studies to then moving into practical applications but there seems no doubt that these studies do help us understand how diseases work and possible treatments. However, there are some caveats to this. What is now needed is to compile a full list of each of the genetic variants that contribute to a disease and how they then influence a disease.

A further factor however is to appreciate that not all understanding about a disease will come from genetic studies, it won’t be able to provide all the answers. This is due to the fact that there may be other factors which influence whether someone develops a disease such as their lifestyle and environment. Obesity here is a good example, where it is clear that what makes a person obese can be a mixture of genetic and environment.