Inheritance of continuous traits can be explained by Mendelian genetics
Contributed by: Sophia Buysse
Agriculture, Agroecosystem, Anxiety, Europe, Fundamental research, Genetics, Historical figure, Lab, Mendelian genetics, Mental health, Plants, Quantitative genetics, Terrestrial, Woman
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The published work comes from Genetica (1941) and is in German. Most of the biography comes from Stamhais (1995) (link) and an English summary of Tammes’ work is included.
Slide 1: Researcher’s Background
Jantina ‘Tine’ Tammes was a botanist and geneticist at the University of Groningen, Netherlands who studied the inheritance of continuous traits in flax.
Biography in brief
Jantina ‘Tine’ Tammes was born in 1871 in the Netherlands. Her father ran a chocolate and confectionary factory, and their family was in the lower-middle class; she had five siblings. Tammes enrolled at the University of Groningen, Netherlands in 1890 as one of few women taking classes. While a student, she founded a walking club for academic women to socialize. However, as a woman, she was able to take classes but unable to take her exams and earn a degree. She was awarded a teaching diploma in physics, chemistry, and cosmography in 1892 and a second teaching diploma in botany, zoology, mineralogy, and geology in 1897. However, teaching certificates were not equivalent to a degree and she remained undervalued by her male colleagues. Tammes taught classes while working as research assistant to Jan Willem Moll. In 1901, Tammes was the first woman in the Netherlands to be awarded a scholarship from the Buitenzorg Fund of the Royal Dutch Academy of Science, a prestigious award to conduct botanic research on the island of Java. More impressively, she did so without being a PhD student. However, Tammes’ doctors advised against her travel for an extended period of time. Tammes suffered from physical health issues with her heart in addition to mental health disabilities including anxiety. She also had the responsibility of caring for her parents, which prevented extended travel.
Tammes’ work was the first research to publish on variation, evolution, and genetics in the Netherlands, and one of the first in the world as genetics was a new field of research. Her research centered around common flax (Linum usitatissimum L.). Her early work described the morphology of flax while later work examined the heritability of continuous traits, such as seed size and flower color, in a Mendelian framework. She was unique in relying on probability to predict the number of genes that may contribute to a continuous trait through the multiple-factor hypothesis (Stamhuis-Monsen 2007). Her work also showed that a second generation hybrid (the offspring of two hybrid individuals) had more trait variation than a first generation hybrid (the offspring of non-hybrids); other researchers at the time found similar results. Her work is thought to be overlooked because Tammes is a woman and her work was primarily published in German rather than English.
Throughout her career, Tammes was an opponent to eugenics. She believed there was much more to learn about heredity in humans, and that the social and economic conditions of society should be priorities for improving the human condition. Tammes published arguments against eugenics throughout her career but was also a member of the Dutch Eugenic Federation (Stamhuis-Monsen 2007; Koertge 2008).
Finally, in 1911, when Tammes was over 40 years old, she was granted an honorary doctorate in zoology and botany from the University of Groningen (Stamhuis, 1995). In 1919, 8 years after her application for professorship was submitted, she became the first professor in the Netherlands appointed to professor of variability and genetics in addition to being only the second female professor (Stamhuis & Monson 2007). She was a mentor to both PhD and MD students as a professor. Tammes retired in 1937 and died in 1947.
Is (or was) their research under-valued because of their identity?
Are there other scientists/research examples that this example can replace or be added to?
Her work can be taught alongside Mendel as she investigated if continuous traits fell within the Mendelian framework and reinforced the ratios expected for traits governed by a number of pairs of alleles [if there is one pair of alleles, expect an F2 generation (second generation hybrid) to have a 1:2:1 phenotype ratio; if there are two pairs of alleles, expect a 1:4:6:4:1 ratio. Her work extended this out to multiple factors (for example, in flax she found that at least 4 factors controlled seed size though an exact number could not be determined].
Stamhuis, I. (1995). A Female Contribution to Early Genetics: Tine Tammes and Mendel’s Laws for Continuous Characters. Journal of the History of Biology, 28(3), 495-531. http://www.jstor.org/stable/4331365
New dictionary of scientific biography. (2008). In N. Koertge (Ed.), Choice Reviews Online (Vol. 7). https://doi.org/10.5860/choice.45-5921
Stamhuis, I. H., & Monsen, A. (2007). Kristine Bonnevie, Tine Tammes and Elisabeth Schiemann in early genetics: Emerging chances for a university career for women. Journal of the History of Biology, 40(3), 427–466. https://doi.org/10.1007/s10739-007-9132-x
Slide 2: Research Overview
Take home message of study
Continuous traits, those like height or seed size, are difficult to explain with Mendel’s laws of inheritance through discrete hereditary factors (what is now known as a single gene with two alleles). This work on common flax (Linum usitatissimum L.) showed that Mendelian inheritance could explain the inheritance of continuous traits through the multiple-factor hypothesis (where multiple genes control the same trait) and Tammes used the trait appearance after hybridization experiments to predict how many genes were controlling the trait based on probability rules and assuming that each allele contributes equally to the trait. When there are n hereditary factors controlling a trait, there are (2n+1) total forms the trait can take in the F2 generation and the frequency of the ith form is predicted by (2n!)/(i!(2n-i)!).
A photo of common flax (Linum usitatissimum L.) flowering in a field. Tammes used hybrids of common flax, shown, and pale flax, which has a white flower, in much of her work.
Slide 3: Key Research Points
Figure 2 shown above shows the distribution of seed lengths for the parents and first (F1) and second (F2) generations of a hybrid cross of common flax and pale flax. Individuals from either parent generation were crossed to create the F1 generation, and two individuals from the F1 generation were crossed to make the F2 generation. The parent distributions can be seen at either end while the F1 distribution is the short dashed line that appears intermediate of the parents, indicating heterozygous individuals, and the F2 is the long dashed line with a wider distribution. The distribution of the F2 generation can be used to infer how many alleles control the trait of seed length. Out of the 222 F2 plants grown, none of them showed a phenotype similar to either of the parent phenotypes. From this, Tammes was able to conclude that at least four alleles control seed length because, according to theory, 2/256 plants are expected to match either parent if there are four controlling factors and she observed fewer than this. Tammes was unable to say with certainty how many alleles were involved because she only had 222 plants, but was able to say there are at least four.
Understanding the genetics and inheritance of continuous traits is still a research question today. Tammes’ work on flax specifically can be applied to agriculture and the knowledge of genetics of continuous traits is used in plant breeding for agriculture purposes. Additionally, understanding the inheritance of continuous traits is fundamental to further research on the evolution of continuous traits and understanding of how genes translate into a phenotype.
While Tammes was an opponent to eugenics which falls into the categories of social justice and equity, her research was neither in the field of eugenics or directly opposed to eugenics.