For many years, this has been a page focused on the genetics of ear lobes. For some people, the ear lobes are connected directly to the side of their head, all the way to the bottom of the lobe. We will refer to those as attached ear lobes. I have attached ear lobes.
For other people, the ear lobe hangs down beyond the point of attachment. We will refer to those as free ear lobes.
At the time I originally wrote this, this trait was considered to be controlled by a single gene. Now we think that there is more involved.
Let's start with genes. Inside most of the cells in your body (not red blood cells) there is a complete set of instructions for your body and how it develops. These instructions are chemicals that fit together into very long molecules called DNA. In a human cell, the DNA forms 46 strands, called chromosomes, which fit together to form 23 pairs. Each pair of chromosomes fits together in a specific way. Arranged along the chromosomes are sequences of chemicals that form genes. Each gene is a part of the chromosome that contains some of the instructions for making you you. Genes control the color of your hair, how tall you will be, the color of your eyes, the color of your skin, and many, many other characteristics, called traits.
Now, it gets even better. Some genes control more than one trait, and some traits are controlled by several genes working together. Some genes turn other genes on or off. Some genes don't do anything that we can detect so far. That does not mean that they are useless, just that we don't yet know what they do. In spite of the fact that scientists have been studying genetics for a very long time, there are huge areas of genetics that we are still exploring, with new discoveries every year.
Depending on the age of the book, you may find references to ear lobes and tongue rolling as single gene traits, but more recent studies indicate that these traits may be more complex. There are a few traits, such as dimples, freckles, and color blindness, that are still (at the time of this writing) thought to be single gene traits. It will be interesting to watch over time to see which of those move to the multiple gene category.