Concept 12 Evolution begins with the inheritance of gene variations.

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George Shull used corn to study gene variation.

Hello, I'm George Shull. I was very interested in Darwin's theories, especially in how variations arise and accumulate in a species. In 1905, I began experimenting with corn hybrids to see how variations are inherited. In an open field, corn plants are normally cross-pollinated by wind. These plants vary a lot in size, vigor, and yield. I started my experiments by self-pollinating corn plants. Look what happened when I self-fertilized these plants for seven generations. I realized that these self-pollinated lines were pure-bred lines of corn, similar to Mendel's pure-bred pea plants. I made several pure-bred lines this way, each carrying a different variation. These pure-bred lines all grew very poorly and had a lower yield compared to corn openly pollinated in the field. When I cross fertilized two pure-bred lines, I noticed an increase in productivity in the hybrids. They grew better than either of the parental strains or those openly pollinated in the field. I counted the kernel rows on each ear as a way to measure yield. Compared to the parental inbred strains, the hybrid offspring had more than double the yield. Compared to corn openly pollinated in the field, the hybrid progeny had a 10-20% higher yield. I saw immediately that "hybrid vigor" was a significant factor in improving corn production. My experiment, which started as a way to study species variation, became a Mendelian analysis of gene inheritance. Most corn grown today is derived from my experimental design and hybrids.

factoid Did you know ?

Dr. Alexander Graham Bell, the man who invented the telephone, was interested in heredity. He donated three of his multi-nippled sheep to the Station for Experimental Evolution for study.


Charles Darwin's theory of evolution caused a renewed interest in the question of heredity. Why?