Zea mays (maize, or corn) was originally domesticated in central Mexico at least 7000 years ago from an endemic grass called teosinte. Teosinte is generally unbranched, has male and female flowers on the same branch, and has few kernels per 'cob,' each encased in a hard, leaf-like organ called a glume. In contrast, maize is highly branched, with a male inflorescence (tassel) on its central branch and female inflorescences (cobs) on axillary branches. In addition, maize cobs have many rows of kernels and soft glumes. George Beadle crossed cultivated maize and wild teosinte, which resulted in fully fertile F₁ plants. When the F₁ plants were self-fertilized, about 1 plant in every 1000 of the F₂ progeny resembled either a modern maize plant or a wild teosinte plant. What did Beadle conclude about whether the different architectures of maize and teosinte were caused by changes with a small effect in many genes or changes with a large effect in just a few genes?

Key Concepts

Genetic Architecture

Genetic architecture refers to the underlying genetic basis of phenotypic traits, including the number of genes involved and their interactions. In the context of maize and teosinte, understanding whether their differences arise from many genes with small effects or a few genes with large effects is crucial for comprehending how traits evolve. This concept helps in predicting how traits can be inherited and modified through breeding.

Quantitative Trait Loci (QTL)

Quantitative Trait Loci (QTL) are regions of the genome that are associated with specific quantitative traits, such as height or kernel number in maize. Identifying QTL can reveal whether traits are influenced by many genes (polygenic) or a few major genes (oligogenic). This concept is essential for understanding the genetic basis of the differences between maize and teosinte, as it provides insights into the complexity of trait inheritance.

Mendelian Inheritance

Mendelian inheritance describes the patterns of inheritance first outlined by Gregor Mendel, which include concepts such as dominant and recessive alleles. In Beadle's experiment, the observation of F₂ progeny resembling either maize or teosinte suggests that the traits may follow Mendelian ratios, indicating the involvement of specific alleles. This concept is fundamental for analyzing how traits are passed from one generation to the next and understanding the genetic differences between the two plants.