I am not sure how to google this but the question is pretty simple: would the genes for the index finger be located "near" the genes for the thumb? Would all genes concerned with the heart be clustered together?


1 Answer 1


There are no “genes that code for the index finger” as such†, but the question is valid in more general terms.

In short the answer is no (or, at least, not necessarily).

This sort of principle is valid to a large extent in bacteria, where genes that work together are part of one transcriptional unit called an operon. The most famous example of this is the lac operon of Escherichia coli which contains a group of genes all concerned with the utilization of lactose as an energy source for this bacterium.

However in higher organisms, this need not be the case, a good example being the genes for the two chains which associate to form the human blood protein, haemoglobin. Despite their similar structure and probable evolutionary relatedness, the gene for alpha globin is located on chromosome 16, whereas that for beta globin is on chromosome 11.

Nevertheless there are some examples of what are termed gene clusters in higher eukaryotes. These are often genes of a single family that have arisen by relatively recent gene duplication. Over longer periods of evolutionary time they can become separated by recombination. One reason that this may not occur so frequently in prokaryotes is that groups of prokaryotic genes are often transcribed into single so-called polycistronic mRNAs — mRNAs that encode all the proteins of the cluster. This allows expression of the genes to be co-ordinately regulated.

Eukaryotic genes do not normally produce mRNAs of this type, and co-ordinate regulation (e.g. for alpha- and beta-globin chains) is achieved in a different manner. Thus, there is no strong selection against disruption of an ancestral cluster.

As always in biology, there are exceptions. Some eukaryotic genes need to be close together, for example those involved in the class specificity of immunoglobulins (the part that determines whether an antibody of the same specificity if in the cell membrane, or in mucous tissues etc.). These need to be close together for the process known as class switching.


† Particular related organs or parts of the anatomy like the different fingers are not encoded by different genes. They are different because of a development programme that determines the fate of precursor cells. That sort of thing lies in the general field of development and embryology, I believe.


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