Mendel’s genetics:
- Mendel started his work on pea in 1856 and derived law of inheritance in 1865.
- Mendel’s work was unfortunately paid no attention and ignored for 34 years. This is perhaps due to the controversies arisen from the publication of Darwin’s book on ‘origin of species’.
- In 1990, three biologists, who rediscovered the Mendel’s laws and found it correct. Three scientist were a Dutch biologist Hugo de Vries, a German botanist Carl Correns and an Austrian botanist Erich von Tschemark.
- After the rediscovery, Mendel’s laws were widely accepted and called Mendel as the ‘Father of Classical Genetics’.
- Before Mendel, other researches have been working on several varieties of plants differing from one another in many complex characters produced fertile hybrids by artificial pollination, but they failed to explain the mechanism of heredity.
- The
following were the two reasons behind their failure:
- They considered simultaneously many characters in which parents differed. This made them confused. Due to confusion they could neither trace the individual characters through successive generations nor they could maintain the complete numerical records of results
- Secondly, they believed that the hereditary characters of two parents (mother and father) become thoroughly mixed in the offspring.
- Mendel did realize the above two causes of his predecessor’s failure. In order to overcome those difficulties he carefully planned experiments exactly on the same pattern as his predecessors had already followed.
- He began his breeding experiments with different varieties of garden peas in 1856.
Reason for the selection of Pea plant
- Mendel made careful selection of garden pea, Pisum sativum as the plant material for his experiments, as it has the following advantages:
- Pea plants possess many varieties with well defined characters. Among 20-30 different characters he choose seven different ‘unit characters’ for his study.
- The flowers of pea plants are bisexual.
- Flower is closed typed such that pollination is limited to self.
- Cross pollination can be easily done by removing stamens before pistils of flower mature by the process called emasculation and cross with stigma of desired pea plant.
- Cultivation of pea plant is easy, economic and required small space.
- Life span of pea plant is short, thus many generation can be obtained in a single growing season.
- The hybrids of pea plant produced by cross pollination are perfectly fertile
Reasons for Mendel’s success:
- The Mendel’s success was dependent on his careful selection of pea plant. He was also lucky that the plant did not show incomplete dominance or epistasis.
- Mendel studied all the seven pairs of differing contrasting characters individually in both original stocks (parent pea plant) and then in the hybrids offspring in different generations. He classified the offspring according to their characters as dominant and recessive and also maintained the record of individuals having particular characters. This quantitative method of recording the number of individuals having particular characters is vital for Mendel’s success
- Mendel studied the inheritance of one character at a time, while his predecessors considered the organism as a whole.
- He carried out experiments to F2 and F3 generations only.