On September 19, 1864, German botanist and geneticist Carl Erich Correns was born. Correns is notable primarily for his independent discovery of the principles of heredity, and for his rediscovery of Gregor Mendel‘s earlier paper on that subject, which he achieved simultaneously but independently of the botanists Erich Tschermak and Hugo de Vries, and the agronomist William Jasper Spillman.
Carl Erich Correns entered the University of Munich in 1885, where he studied botany and was supported by Karl Nägeli, a botanist whom Mendel corresponded with on the subject of his pea plant experiments. At the University of Tübingen, Correns became a tutor and later the first director of the newly founded Kaiser Wilhelm Institute for Biology in Berlin-Dahlem.
Correns started to experiment with trait inheritance in plants during the early 1890s. While he devoted his time to the hawkweed plant experiments that Mendel carried out, he was apparently not aware of the pea plant results. In 1900, he published his first paper in which he cited both, Charles Darwin and Gregor Mendel, even though he probably never fully recognising the relevance of genetics to Darwin’s ideas.
In the field of cytoplasmic inheritance, Correns performed experiments with the Mirabilis jalapa in order to research apparent counterexamples to Mendel’s laws in the heredity of variegated leaf color. He observed that while Mendelian traits behave independently of the sex of the source parent, leaf color depended greatly on which parent had which trait. Pollinating an ovule from a white branch with pollen from another white area resulted in white progeny, the predicted result for a recessive gene. The green pollen used on a green stigma resulted in all green progeny, the expected result for a dominant gene. If green pollen fertilized a white stigma, the progeny were white, but if the sexes of the donors were reversed the progeny were green.
Later on, this non-mendelian inheritance pattern was traced to a gene named iojap. It codes for a small protein required for proper assembly of the chloroplast ribosome. In the iojap, when the mother is homozygous recessive, then the protein is not produced, the chloroplast ribosomes fail to form, and the plasmid becomes non-functional because the ribosomes cannot be imported into the organelle. If a white father is paired with a green mother with functional chloroplasts, the progeny will only inherit functional chloroplasts, and will thus be green. Carl Correns published his results in 1909 and in his paper, he established variegated leaf color as the first conclusive example of cytoplasmic inheritance.
References and Further Reading:
- Carl Correns at Britannica Online
- Re-discovering Mendel: The Case of Carl Correns
- Carl Correns at Today in Science