Abstract
Gregor Mendel (1822–1884) was a Moravian biologist from whose quantitative plant breeding studies were derived laws of inheritance that founded a new branch of biology, genetics. He crossed varieties of peas and examined the distribution of characters among offspring over successive generations. Hybrids resulting from crossing two varieties with contrasting characters did not breed true. They were not the ‘constant hybrids’ much sought by professional breeders that might lead to independent species. In the 1880s Mendel's work was appreciated by Wilhelm Focke and George Romanes, who initiated similar studies with animals. Studies with plants were initiated in the 1890s by European botanists who discovered Mendel's work in 1900. A relationship of hereditary units that determined characters – now known as genes – to chromosomes was noted by cytologist Michael Guyer in 1900. The major early advocate of Mendel's work, zoologist William Bateson, agreed with Mendel that new species could emerge discontinuously.
Key Concepts
- For his experiments it was essential that Mendel chose characters in pea plants that would breed true.
- He found that hybrids between lines which themselves bred true, did not breed true. They were not ‘constant hybrids’.
- At that time many thought that constant hybrids would indicate a continuous species origination process.
- From ‘brother‐sister’ matings of pea hybrids, Mendel derived quantitative laws.
- His units that determined characters – now known as genes – were located to chromosomes by Michael Guyer.
- Without knowledge of Mendel's laws, European botanists rediscovered them in plants.
- William Bateson confirmed that Mendel's laws applied to various animal and plant species.
- Mendel's laws were challenged by mathematical biologists (biometricians).
- Mendel followed the statistics of his time and his results have withstood the test of time.
- Mendel's view that new species can arise discontinuously without the involvement of natural selection has gained support.
Keywords: heredity; constant hybrids; Mendel's laws; genetics; chromosomes; speciation; Carl von Nägeli; George Romanes; Michael Guyer; William Bateson