Carl Franz Joseph Erich Correns

1864-1933

German Geneticist and Botanist

Carl Correns was one of three scientists who simultaneously rediscovered the work of Gregor Mendel (1822-1884). Correns investigated and confirmed the validity of many Mendelian laws and showed a deep understanding of Mendelian genetics. Correns's research was the first to correlate Mendelian segregation with the reduction division of chromosomes, and he illustrated several important examples of deviations in Mendelian inheritance, such as natural variations in the dominant-recessive heredity pattern.

Correns was born in Munich to a Swiss mother and German father who was a member of the Bavarian Academy of Art. An only child who was orphaned at age 17, Correns contracted a case of tuberculosis that delayed the degree he finally received from the University of Munich in 1889. He married Karl von Nageli's (1817-1891) niece Elizabeth Widmer in 1892. He served as a lecturer, then assistant professor, at the University of Leipzig, became full professor at Munster, and finally in 1913 was appointed the first director of the Kaiser-Wilhelm Institute of Biology in Berlin. He served at this post until his death.

Working with Nageli during his early career, Correns was at least partially restricted to investigations that sought to extend the work of his mentor Nageli. His research focused on heterostylism, in an attempt to counter and critique Charles Darwin's (1809-1882) views on adaptations to outbreeding. Correns's research denied the idea that pollen grain size variations were adaptations to flower styles, and he further challenged Darwin regarding his conclusions on the effect of increasing temperature on the sensitivity of leaves. Correns's research also included a study of plant cell wall growth, as well as floral morphology, the physiology of climbing plants and plant sensitivity, leaf primordia, and moss and liverwort vegetative reproduction.

In the 1890s Correns examined the hereditary effects of pollen on developing embryos by cross breeding varieties of peas and maize. He discovered that his pea stock progeny had produced color traits that exhibited very simple ratios, while his maize research produced a much more complicated set of results. As Correns was attempting to reconcile the meaning of his conflicted pea and maize breeding results, he read Mendel's previously overlooked and forgotten work, which verified his own results. In 1900 Hugo de Vries (1848-1935) published his own work on hybridization and his rediscovery of Mendel's research, and Correns was forced to quickly write up and publish his already completed work.

Correns dedicated his remaining career to investigating the validity of Mendelian laws. He was able to correlate the reduction division of chromosomes with Mendel's law of allelic segregation. Correns subsequently discovered an example of coupling of hereditary traits in a strain of maize that conjugated self-sterility with blue coloration. This data was evidence of variation of Mendel's law of independent assortment. Correns also developed a theory of chromosome inheritance that allowed for the occurrence of crossing over, or gene exchange between chromosomes. Correns also predicted and experimentally proved the Mendelian inheritance of sex.

Correns concluded his research career studying the inheritance of variegation in leaves, and he documented the occurrence of cytoplasmic inheritance in the form of plastid DNA. His experiments illustrated that plastids were extra-nuclear units of inheritance that could produce variegated leaves, and that variegation could also be inherited through nuclear genes or even be a non-inheritable form. Correns was able to prove that the plastid source was predominantly the egg and not the sperm. Plastids have since been shown to carry important genes such as those related to disease and drug resistance.

Though considered an average lecturer, Correns was hard working and dedicated to science. He had an approach to Mendelian genetics that was thorough, well developed, and considerably advanced for his time. Correns's place in history consists of both his rediscovery of Mendel's work and his eloquence, skill, and sophistication as a Mendelian geneticist.

KENNETH E. BARBER