I’m going to be honest. I have been waiting for When A Gene Makes You Smell Like a Fish…and Other Tales about the Genes in Your Body to come out in paperback. It is one of those books where you are so immersed in the stories you only realize later, after you put it down, how much you have learned. Author Lisa Seachrist Chiu tells stories about rare and not so rare genetic quirks while explaining modern genetics. Below we have excerpted the beginning of chapter two, Just One Bad Apple, this afternoon we will look at the Long Stretch Gene.
Your third-grade teacher was right. Sometimes it takes only one bad apple to spoil the barrel. In other words, for some genetic disorders, just one faulty gene serves as the trigger. Inheriting it from either your mother or your father pretty much ensures you will have the condition yourself. This is termed “autosomal dominant inheritance”—the word autosomal simply refers to the fact that the gene for whatever condition doesn’t reside on either of the sex chromosomes. The word dominant means inheriting one gene is enough. For example, if your father had an extra finger or toe next to his pinky finger or toe, you and your brothers and sisters each would have a 50 percent chance of having an extra digit as well.
When a gene produces a dominant trait such as an extra digit, the inheritance pattern displays some typical features. The first was already mentioned; each child of an affected parent has a 50 percent chance of developing the disorder. In addition, the condition doesn’t skip generations. If your father is, in the words of the Princess Bride’s Inigio Montoya, a “six-fingered man,” and none of his children have six fingers or toes, then none of his grandchildren or great grandchildren will inherit the trait from him. Autosomal dominant traits affect males and females in roughly equal numbers.
Autosomal dominant inheritance is the most straightforward inheritance scheme in Mendelian genetics. Yet even among autosomal dominant diseases there can be some complexity. For example, sometimes more than one gene can lead to the same phenotype as is the case for familial hypercholesterolemia, a condition that can cause very high cholesterol levels. What’s more, other genes and environmental influences can also play a role in determining when or how severely someone is affected with a dominantly inherited disease. Dominant genes provide the closest genetic example of fate, but it may be fate with an asterisk.