Discontinuous variation occurring in Biscutella laevigata
Contributed by: Chloe Pak, Lauren Johannes @laurenjohannes4, Clare Collins @clareccollins, Lucia Wyland @lucia_wyland, & Mandie Flint @mandie__26
Keywords
Agriculture, Biome, Development, Ecology, Europe, Evolution, Experimental, Field, Fundamental research, Genes, Genetics, Historical figure, Molecular biology, Natural history, Physiological/organismal ecology, Plants, Terrestrial, Woman
Slides
Note: click the gear symbol to see notes that accompany the presentation
View and download in google slides here
Resources
Celebration of Edith Rebecca Saunders link Accessed 24 Sept. 2020.
Richmond, Marsha L. “The ‘Domestication’ of Heredity: The Familial Organization of Geneticists at Cambridge University, 1895-1910.” Journal of the History of Biology, vol. 39, no. 3, 2006, pp. 565–605. link
Saunders, E. R. “On a Discontinuous Variation Occurring in Biscutella Laevigata.” Proceedings of the Royal Society of London, vol. 62, 1897, pp. 11–26. link
Podcast: “The Untold Story of Edith Rebecca Saunders—’mother of British Plant Genetics’.” Genetic Literacy Project, 28 Oct. 2019, link
Notes
Slide 1: Researcher’s Background
Edith Rebecca Saunders (Born 1865 in Brighton, England- Died 1945) was a British geneticist and plant biologist. She is known as the “Mother of British Plant Genetics”
Biography in brief
Edith Rebecca Saunders attended Newnham College at University of Cambridge at 19 years old and earned many scholarships and an equivalence of a first class degree in Physiology in 1888. Upon graduation, Newnham College hired her, and she worked there for the entirety of her career as a teacher and fellow, teaching and conducting research, until 1925. There is not much known about the personal life of Saunders. Her husband, friends, colleagues and students described her as a stoic yet energetic individual who had an intense passion for her scientific work, which is showcased among her many accomplishments.
As a labeled Botanist, Saunders specialized in the genetics of plants, doing a large part of her research with colleague William Bateson, who was also a geneticist. Together, they specialized in plant breeding and focused largely on discontinuous variation in Biscutella laevigata. Through their research, Saunders and Bateson invented some of the terminology used in Genetics, such as ‘allelomorph’ [allele today]. Saunders was also the first to notice the existence of the phenomenon initially called ‘coupling’. Saunders and Bateson were working on much of the same plant research as the famous Mendel at the time, and they were key characters in the rediscovery of his theories.
Is (or was) their research under-valued because of their identity?
Yes
Are there other scientists/research examples that this example can replace or be added to?
Mendel gets the most credit for this line of plant genetics. She worked with Bateson and Punnett very often, but she did not get as much recognition as they did.
Slide 2: Research Overview
Take home message of study
Saunders was known for research “On a Discontinuous Variation occurring in Biscutella laevigata” which was the title of her paper. It was received by the Royal Society of London through William Bateson since women couldn’t be a part of the society, but even with Bateson’s help with her research, her findings were completely her own. Discontinuous variation occurs when there are distinct, qualitative variations in the phenotypic expression of a trait due to genetics (e.g., human blood type). The opposite of discontinuous variation is continuous variation–values of the trait vary gradually over a range (e.g., height and weight).
Study system
Saunders’ study system was the Biscutella laevigata, or more commonly known as the buckler mustard (middle and right photos). It is a perennial herb that can be found in Europe, but specifically, Saunders and Bateson found theirs in the Italian Alps. Saunders observed that some of these plants were hairy, while others were smooth. She then set up an experiment to test out why this was the case. She questioned if in nature, could a hairy plant and a smooth plant intercross to produce a “blend” of hairy and smooth. As Saunders observed the plants’ hairs, she realized that this was an example of discontinuous variation. The leaf surfaces between different plants could vary so much in the amount of hairs that were present, it became evident that this was clearly a variation from genetics rather than environmental influences. Saunders classified the Biscutella laevigata into three different categories: surface hairy (middle photo), surface intermediate, and surface glabrous (smooth). Surface hairy is when both the upper and lower surfaces are thickly covered in hairs. Surface intermediate is when there are a few hairs on the upper surface, or there are hairs grouped together with occasional smooth areas. Finally, surface glabrous is when the whole upper surface is smooth with rare instances of hairs, or the surface is completely lacking hairs. Saunders thoroughly described the details of her experiment in her research paper. She collected the seeds from Val Formazza (a commune in Italy), and raised three different sets of Biscutella laevigata (grown in August 1895, February 1896, and March 1896, respectively). She raised the seedlings in pots out in the open, but eventually she would have to place the pots around cinder or surround them with soot to protect them from invading slugs and snails in order to obtain accurate data. From her data, Saunders noticed that the offspring from the first generation looked more like their parents compared to later generations. Also within the first generation, it was more likely that a hairy parent and a smooth parent would produce either hairy or smooth offspring, instead of the predicted “blend”. The “extreme types” (very hairy or very smooth) proved that discontinuous variation was happening within the Biscutella laevigata. Saunders then wanted to test what the offspring would look like in future generations, and she completed this experiment in the summer of 1896. She discovered that the next generations weren’t as “extreme” and that there were more surface intermediates compared to the first offspring generation.
Slide 3: Key Research Points
Main figure
This table is found in Saunder’s paper. This data describes the last generation of intercrossing for this study, and the colored boxes were added to describe the figure better. The type of cross is stated in the top green box. The expressed traits of the offspring are found in the blue box on the left side. The values in the body of the figure are the number of offspring from the parent on the top with the expressed trait on the left. Please note that the data was collected when the plants were young seedlings. Saunders found that when a hairy plant breeds in any way with a smooth plant, the offspring had hair as shown by the lack of values in the red square. They did not tend to have an extremely hairy surface–only 8 plants had the extreme hairy surface with this cross and most had some sort of intermediate form of hairy surface. She writes, “it would appear that when the extreme forms are intercrossed the offspring seldom exhibit the degree of hairiness characteristic of the more hairy parent” (Saunders, page 22). The offspring on the far right side shows that when a less extreme smooth surfaced plant is fertilized by a hairy plant, the cross results in offspring with an increased level of overall hairiness. This data supports Saunders prediction that Biscutella laevigata vary because of genetics, or in other words, they do express discontinuous variation. She does note that hairy seedlings persist in hairiness as they grow, but the intermediate condition of hairiness in young seedlings tend to gradually become more and more smooth until full-grown Biscutella laevigata.
Societal Relevance
Saunders’ main contributions to science were focused through the lens of genetics. With William Bateson and Reginald Punnett, she discovered genetic linkage. This is the tendency for DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Additionally, her work with Bateson led to the defining of alleles. As mentioned before alleles are a variant form of a given gene, meaning that it is a mutation on the same place on a chromosome. Research into alleles has accelerated modern medicine by aiding in the understanding and prevention of genetic disorders. An example of this is red-green color blindness which is an inherited condition due to the recessive alleles. Due to the findings of Saunders, we are now able to predict the occurrence of genetic disorders such as cystic fibrosis which is caused by recessive alleles and Huntington’s disease caused by dominant alleles. Saunders was a pioneer for modern genetics and her work has contributed to modern medicine by helping us understand and prevent genetic disorders as well as how genes are passed down from parents to offspring.
