A Fifth Question for Seder night: What am I passing on to the next generation?

In Every Generation? Help Jnetics ensure that severe genetic disorders are not passed on to the next generation.

by Josh Forman, Head of Science, Education & Outreach

Pesach is a time when we think about family, history, ancestry and the future. Sitting round the Seder table, the themes of the festival prompt conversations about who we are as a people, where we’ve come from individually, and how we ended up the way we are.

We might play a game of spot the differences – or similarities – between everyone in our families: who resembles who? What characteristics did one or other of us inherit from generations past? ‘Oh, you’ve got your bubbe’s beautiful green eyes but sorry to say, you got your dad’s nose!’

But there is so much more to these wonderful observations. As well as the familial ‘look’, there are our learned habits and mannerisms (which are not from our DNA). There are specific traits, like needing glasses, being tall or short or athletic. These aspects are often rooted in genetics, at least partially.

As a scientist and educator, I’m fascinated by where these genes and characteristics come from. For example, did Moses have the typical ‘Israeli’/middle eastern look? I don’t imagine him looking very Ashkenazi. In my mind, he must have had dark skin, dark hair and dark eyes. But was he tall? Did he speak with his hands?

Jewish history has seen us move around considerably over the centuries, to all parts of Europe, the Middle East and Africa. Geneticists have traced back the founding of the Ashkenazi population of Jews as emanating from Eastern Europe, probably from a community of around 350 people during the 13th century.

Over the centuries, the genes of that original group have mixed with and incorporated those of others around them; and they were exposed to different environmental challenges, causing what’s known as ‘genetic drift’. This is a mechanism of evolution in which there are random fluctuations in the frequency of a particular version of a gene. Specific traits can be reduced or raised in prominence over a relatively short time (in evolutionary timescales). In small, isolated populations, such as Jewish ones, this is particularly pronounced.

So, while we pass down our genes and characteristics alongside our traditions and values , marriage and reproduction within a small community has caused specific traits to become more common. The unfortunate side effect of this is a higher prevalence of certain genetic diseases. BRCA is garnering the headlines for this at moment, with one in 40 Ashkenazi Jews and one in 140 Sephardi Jews having a cancer-causing version of this gene. This compares to one in 250 people in the general population.

Many diseases in the Jewish community work in a similar manner in terms of prevalence – though they manifest differently. Common recessive genetic diseases include Tay-Sachs, Cystic Fibrosis, Canavan Disease and Familial Dysautonomia. More than a third of all Jewish people carry at least one disease-causing gene. Carrying the gene doesn’t cause the condition itself but matched with a partner who does carry the same disease-causing gene, risks it being passed to any children. 

We are an endogamous people – one that tends to marry within the community. It’s kept the Jewish people in existence for millennia, with all the wisdom and richness of our heritage being passed down the generations, but in genetic terms, it’s not always good.

Thankfully, we live in an era blessed with phenomenal technological advances that arm us with the scientific know-how to check our genes, and ensure we don’t pass anything we don’t want to. All we need to do is brush a swab on the inside of our cheek and send it off for checking – a modern-day miracle – not just for Pesach.