Community Magazine June 2009

52 COMMUNITY MAGAZINE Richard Zafrani Genetics 101 Genes are, essentially, the blueprint of a person’s physical makeup which is contained within each cell of the human being. Every person has in his cells forty-six chromosomes, or packages of genes, which he receives from his parents – twenty-three from each. When we speak of a genetic disease, we refer to a mutation of one of a person’s genes, which can result in a physical disorder. The mutation works almost like a defective computer program: it gives the body bad instructions for how to develop. In other words, it tells the body to do the wrong thing. As opposed to illnesses brought on by viruses or bacteria, these disorders are integral to the person’s physical makeup, and there is thus no possibility of curing the disease by targeting an invading microorganism. Nor is there any way of protecting the body from contracting the illness through a healthy lifestyle. Moreover, since genes are reproduced in one’s children, a genetic mutation in a parent can be transferred to the child. It must be emphasized that not everybody with a defective gene will necessarily suffer the related disorder, or transfer the defect to his or her children. This depends, largely, on whether the gene is question is “dominant” or “recessive” and whether the gene passed on to the child is normal or defective. Recall that a child receives two copies of every gene – one from each parent. If one of the parents possesses one particular faulty gene, and passes that gene on, the child receives both that defective copy and also one normal copy of the gene from the other parent. In the case of a dominant disorder, the defective gene is capable of “dominating” the corresponding normal gene and affecting the child. Any child produced by such a union thus has a 50 percent chance of inheriting the defective gene and suffering from the disorder. Thankfully, many (though certainly not all) of the common genetic disorders, including Tay-Sachs, are of the “recessive” type, which means that the mutated gene typically gives way to the normal gene. Practically, this means that if only one parent has the defective gene, no children will suffer from the disorder. Each child has a 50 percent chance of becoming a “carrier” like that parent, but none of the children will contract the disease in question, because the ordinary gene received from the other parent will dominate. A recessive disorder can affect a child only if both parents share the mutation in question. Assuming both parents are only carriers, each child of such a marriage stands a 25 percent of inheriting the disorder, a 25 percent chance of being entirely unaffected by the mutation, and a 50 percent chance of being a carrier. A carrier is completely healthy and shows no physical effects of the mutation, but has the possibility of passing the mutation to his own children, if he marries another carrier. B eing the Chosen Nation has never been easy. Though it a status that we are deeply proud of, in every generation Jews have had to earn this distinction, confronting numerous challenges on a variety of different fronts. One particular challenge, inexorably bound in our DNA, has faithfully followed us generation after generation. In modern times, scientific research has revealed the unique challenges posed by “Jewish genes” – the potential among Jewish couples to produce children that have certain diseases in greater frequency than the general population. Much attention has been paid in recent years to disorders that affect Ashkenazim, but contrary to popular belief, Jews of Sephardic origin are not immune to genetic disorders. Is it time for Sephardic Jews to think about large-scale screening, like their Ashkenazic brothers? B p Sephardic Genetics EXPOSED!