The principles of heredity have been around since long before scientists knew much about genes and chromosomes. Gregor Mendel, known as the first to study heredity scientifically, was an Austrian monk who tried to crossbreed garden peas in the 1880s and stumbled upon the two main genetic principles of segregation and dominance, and independent assortment. Mendel chose the pea plants because he would be able to observe the inheritance patterns in up to two generations each year (modern geneticists use plants that reproduce more quickly) [source: O'Neil].
Mendel crossed red-blossomed peas with white-blossomed ones, and instead of getting pink-blossomed peas, he still got red. After crossing the next generation of red-blossomed peas, Mendel got approximately three red-blossomed plants for every white one. Mendel realized that each plant had a pair of "factors" (or genes) -- one from each parent plant. Each pair separated before forming a new plant so the new one would also have just two factors. Because plants with white and red parents came out red, Mendel decided that red was the "dominant" factor. Only plants with two recessive white-blossom factors could turn out white. This research led Mendel to establish the first two principles of heredity.
Ever since Mendel's first experiments, the study of genetics and heredity has been complicated, but it can be broken down into six main principles:
- Segregation and dominance
- Independent assortment
- Linkage and crossing over
- Sex determination
- Sex linkage
- Interaction of genes
Segregation and dominance, as well as independent assortment, were discovered by Mendel in his work in the 1880s; others were added or modified based on later geneticists' theories.
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