The Hox Genes Essay

1166 words - 5 pages

The Hox genes are a set of related genes that code for transcription factors involved in determining the general body plan of an organism along the anterior to posterior axis. One unique feature of the hox gene is that its function and presence is highly conserved in a wide range of species, including the model organism Drosophila, amphibians, and mammals. Because of such a high level of homology amongst species where this gene cluster exists, conducting research using model organisms containing the hox gene cluster can lead to relevant discoveries in higher organisms and help to better understand evolutionary diversity. Another notable conserved feature of the hox genes is that they display colinearity, meaning that are they expressed along the anterior-posterior axis in the same order that they are organized within the chromosome. It is ultimately the HOX protein distribution that dictates the varying body architecture within a wide range of organisms that rely on the hox gene expression.
In Drosophila, there are eight hox genes, which are generally divided up into two complexes, the antennapedia and bithorax. The antennapedia complex contains genes responsible for coding for the head and thorax regions of the body and begins at the 3’ end of the DNA sequence making up the homeotic gene cluster. On the other hand, the bithorax complex codes for the abdominal region of the body and is located at the 5’ end of the DNA sequence. While the pair-rule and segment polarity genes are the ones that establish the segments along the body of the fly embryo, it is the homeotic genes that then assist in determining the identities of each specific segment. This ultimately leads to a distinct anterior-posterior polarity along the length of the body. Each of the eight hox genes code for a specific segment of the fly’s body. A well-known experiment used to better understand the role of hox genes in Drosophila is a knock out of individual genes. This leads to a transformation that causes one body part to develop into another. For example, a mutant antennapedia gene, the fifth in the set of hox genes, will result in legs developing on the fly’s head, rather than antennae. Several other variations of this experiment can be done, where a gene being knocked out result it’s in incorrect body segment formation.
In vertebrates, hox genes are first expressed in the developmental stage of gastrulation, where the major body axis pattern of the embryo is formed. One major difference in expression of hox genes is whether they are expressed in invertebrates or vertebrates. Here we will look at some of the distinct differences that exist in vertebrates, beginning with amphibians. Oftentimes, amphibians are used to study the function of the hox genes in limb development, specifically Hox9 to Hox13. One area of particular interest in amphibians is the absence of the fifth finger in some organisms. It is believed that there is a difference in the...

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