Homeobox mutations! If you’ve dipped your toes into developmental bio you might’ve heard of Hox genes—those are a type of homeobox gene that control head-to-tail body order. The coloring on the flies represents a rough Hox map.
Transcript below the cut.
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Homeobox genes are a group of genes that can switch other genes on or off during an embryo’s development. They are involved in many developmental areas, including defining the order and type of limbs and organs. Homeobox genes don’t build these structures themselves, but instead act as a director to manage other genes that carry out the work.Because homeobox genes can initiate or stop a long cascade of development, mutations can result in significant changes to the order, number, or completion of body parts.
For example, switching certain fly genes “on” where they should be “off” can produce a leg instead of an antenna (gene: Antennapedia), or a second set of wings (gene: Ultrabithorax).
Many homeotic mutations have been documented in humans, including the common hereditary conditions of polydactyly (extra fingers and toes) and syndactyly (fused fingers and toes). Thalidomide, a drug marketed as a sedative and anti-nausea pill for pregnant women in the 1950s, gained notoriety after babies were born with severe limb and organ defects. Nearly half died within a year of birth. These conditions were homeobox mutations induced by the thalidomide*.
*Thalidomide is now used to treat cancer and leprosy. Its homeobox mutations only affect embryos—not adults. However, a few babies are born each year with thalidomide conditions as a result of unplanned pregnancies during treatment.
