Hitchhiker’s thumb is a genetic trait that causes the thumb to bend back when extended. It is a recessive trait that can appear to jump in and out of a family. It is not the same as being jointed and has no advantage or disadvantage. Studying recessive genetic traits can reveal interesting information about family and regional histories.
Someone who has a thumb that bends back when extended is said to have a hitchhiker’s thumb. This is a genetic trait and does not interfere with normal thumb function. Hitchhiker’s thumb is also not linked to other genetic conditions; it’s just an interesting phenotype, similar to people who can curl their tongue. To see if you have a hitchhiker’s thumb, clench your fist and extend your thumb. If you notice significant curvature, you have inherited this trait.
Hitchhiker’s thumb is a recessive trait, which means that people must inherit the gene from both parents for it to occur. People can also carry the gene without exhibiting the trait, by inheriting the gene from only one parent. Recessive traits are particularly interesting because they can appear to jump in and out of a family for no apparent reason, thanks to the fact that they can nestle in generations of genes before manifesting themselves.
Some people with hitchhiker’s thumb are able to bend the thumb joint to extreme degrees that may seem uncomfortable to people who don’t have this genetic trait. You may also hear the hitchhiker’s thumb referred to as “thumb hyperextension” in reference to this. There’s no particular advantage or disadvantage to having a hitchhiker’s thumb, and it certainly doesn’t predispose people to hitchhiking.
Having a hitchhiker’s thumb is not the same thing as being jointed. People with double joints exhibit a trait known as hypermobility, which allows them to move their joints much farther than normal. In this case, all the fingers on the hand can be bent and twisted in interesting ways, in addition to the thumb.
Studying recessive genetic traits can be very interesting, because it can reveal intriguing information about family and regional histories. Some teachers like to use the hitchhiker’s thumb in classroom exercises that demonstrate basic principles of genetic inheritance, showing students what a hitchhiker’s thumb looks like and then encouraging them to collect data from classmates. In some families, such traits may become topics of discussion and comment, children being told that they have “inherited Aunt So-and-so’s thumb” to give them a deeper connection with the rest of the family.
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