The human genome has been described in many ways: ‘the book of life’, a set of instructions, a language to be decoded. For many scientists it is a huge data set to be collected and analysed. Besides the metaphors associated with the concept of the genome, visual representations have played an important part in it’s formation.
‘Inscripitons‘ of the genome created by scientists have changed over the years as a result of a greater a understanding of the science, developments in laboratory techniques and advances in technology. Here are some images collected over the years by Wellcome Images:
From the 1950s chromosomes became the visible manifestation of the genetic matter transferred from one generation to the next. Visible for a brief period in the cell, they could be stained and photographed under a microscope. When the full complement of human choromosomes – 46 – was determined, these photographs could be cut and pasted and arranged in order of size into a karyotype – a representation of all the human genetic material they contained.
While chromosomes couldn’t tell you about individual genes, they did show abnormalities and damage at the chromosome level. These abnormalities pointed to certain genetic disorders such as Down’s Syndrome, thus making a link between laboratory science and clinical medicine.
Chromosomes can be broken down into fragments of DNA for detailed analysis. With the use of electrophoresis to separate fragments in the 1970s, DNA fragments containing radioactive markers could be identified in the form of autoradioraphs. In 1984 the first genetic fingerprint was created leading to the development of genetics in forensic science.
By the 1990s techniques for including fluourscent bases in the cloning process used to produce vast quantities of DNA led to the automation of large scale sequencing. Aided by the Human Genome Project, technology such as the use of a laser to ‘read’ colour coding meant that the results of genome sequencing could be displayed directly as computer output:
The sequencing could also be represented graphically, with the peaks indicating the occurrence of bases and with further computer analysis this translated into the familiar ‘ACGT’ code shown at the top of the graphical display.
From the photographic karyotypes of discrete chromosmal forms in the 1950s, through schematic ideograms and autoradiographs of fragments of DNA, a representation of the genome as a linear sequence of the DNA contained in all the chromosomes emerged.
While this was a useful reference point for genetic research, it was not particularly useful for medical genetics, where clinicians needed to isolate and identify specific genes or mutations that indicated genetic diseases. For this purpose they produced specific genome maps of pathological organisms such as malaria, and mutations in different cancers.
Nor is this the end of the story. As well as the physical mapping, associating specific genetic traits with ‘landmarks’ on the genome, linkage maps display the relative position of genes on a chromosome, but it is difficult to show this in a linear display of all the chromosomes end to end. Many maps now display the genome in a circular form, with a ring of chromosomes on the outside and concentric rings representing physical and link data as well as associations across chromosomes:
The DNA double helix has become a symbol for the science of life. Might some depiction of the genome become equally iconic one day?
Hogan A. The ‘morbid anatomy’ of the human genome. Medical History 2014; 58: 315-336.
Author: Lalita Kaplish is Assistant Web Editor at the Wellcome Library.