Mendel in his pea genes

 

Those who have studied genetics at school or university would have heard of Gregor Mendel and his experiments on heredity. Mendel was a monk and abbot based at St Thomas's Abbey in the city of Brno, in what is now the Czech Republic but in his day was part of the Austrian Empire. Mendel is considered the founder of modern genetics due to his detailed experiments on pea plants which he conducted between 1856 and 1863. He studied 7 traits or characteristics of pea plants (things that we would now call phenotypes) and through meticulous breeding experiments established the basic rules of heredity.

Although he probably did not realise it, Mendel was ahead of his time and the significance of his work was largely ignored until the early 20th century, when its importance was realised by others. We now know that many phenotypes in humans and other organisms follow Mendel's rules of inheritance, including most genetic diseases that are caused by single gene defects, including Hereditary Haemochromatosis and Ehlers Danlos Syndrome which are both subjects of previous SangerArtworks.

I have wanted to make an artwork featuring Mendel since I started Dan's DNA but did not have a good sequence to combine him with. Of course the pea genome sequence is the ideal accompaniment for Mendel but at that point the pea (scientific name Pisum Sativum) genome had not been fully sequenced.

Back in 1997, a study from researchers at the University of Tasmania found the genetic variant most likely responsible for the pea stem length phenotype (Le) that Mendel studied (see here for publication). They found a single base change (c.685G>A) in the gene encoding gibberellin 3 beta-hydroxylase, leading to an amino substitution in the protein (p.Ala229Thr). Dwarf plants are homozygous for the c.685A variant (AA), whereas tall plants can be either homozygous for the c.685G variant (GG) or heterozygous (GA).  The dwarf phenotype is an example of recessive inheritance, something that Mendel discovered when he crossed pure-bred tall plants with pure-bred dwarf plants. The offspring from these first crosses were all tall but the dwarf phenotype appeared again in the 2nd generation of plants in the ratio of 3 tall plants to 1 dwarf plant. The diagram below shows the type of experiments conducted by Mendel with the underlying gibberellin 3 beta-hydroxylase c.685G>A genotypes of the pea plants in each generation.

Traits/phenotypes studied in Mendel's pea experiments

  1. Plant height

  2. Pea shape

  3. Pea colour

  4. Pod shape

  5. Pod colour

  6. Flower colour

  7. Flower position

Like humans the pea is a diploid organism, meaning that it has 2 copies of its genome per cell. Its genome is spread across 7 chromosomes and is a total of 4.5 billion base pairs long. The first version of the pea genome sequence was published in September 2019 in the journal Nature Genetics. The reference genome that covers 3.9 billion of the 4.5 billion bases is what I used to create the "Mendel in his pea genes" artwork. I downloaded an 8000 base sequence from the Reference Pea Genome Browser that encompasses the gibberellin 3 beta-hydroxylase gene and created a Sanger sequencing chromatogram from it. I centred a double peak corresponding to the heterozygous c.685G>A variant in Mendel's right eye, symbolising that it was this DNA sequence change that was underlying his observations on pea plant height over 150 years ago.

The artwork is designed to be viewed both closeup - to reveal the DNA sequence, and far away - to reveal the image. The closeups that you can see at the bottom of the screen reveal some important details. The origin of the sequence and other features contained within it are shown in the bottom right corner. I have used the bases after 8000 to sign and date the artwork with a hidden “Sangerism”.

The sequence is centred around the gibberellin 3 beta-hydroxylase gene on Pisum Sativum chromosome 5 or linkage group 3 (chr5LG3). A heterozygous variant (represented by a double peak) is shown at position 3438 of the chromatogram and corresponds with the G to A variant at position 685 of the coding sequence (c.685G>A) resulting in the amino acid substitution p.Ala229Thr in the gibberellin 3 beta-hydroxylase protein. This variant in centred on Mendel's right eye, symbolising the underlying molecular basis of his observations on inheritance.

 

There are 27 rows of sequence at 300 bases across, designed to be printed at a size of around 22x22 in or 55x55 cm.

You can purchase this artwork in a number of different formats from Society6 or Redbubble using the links below.

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© 2021 by Daniel Wallace