Experiments performed by Mendel on genetics and description of mechanisms of hereditary processes and formulation of principles are known as mendelism. Mendel postulated various experimental laws in relation of genetics.
Gregor Johann Mendel (1822-1884) :-Mendel was born on july 22,1822 at Heinzendorf in Austria. In 1856-57 he started his historical experiments of heredity on pea (pisum sativum) plant . His experimental work continued on pea plant till 1865 (19th century). The results of this experiments were published in the science journal in 1866. This journal was published by Natural History society of Bruno”. A paper of Mendel by the name of Experiment in plant Hybridization” published in this journal. Mendel was unable to get any popularity, No one understood of him he died in 1884 without getting any credit of his work (due to kidney disease(Brights disease). After 16 years of Mendel death, in 1900 mendel postulates were rediscovered. Rediscovery by three scientists independently:
- Carl Correns –Germany (Experiment on Maize).
- Hugo de vries (Holland) (Experiment on Evening primrose)- He republished the Mendel results in 1901 in Flora magazine.
- Erich von tschermak –Austria (Experiment on different flowering plants) the credit of rediscovery of mendelism goes to three scientists. Correns gave two laws of mendelism (Low of heredity/Inheritance/mendelism)
Ist Law – Law of segregation.
2nd Law- Law of independent assortment.
Mendel experiments remain Hidden for 34 years.
Mendel results remain hidden due to :
- At that time darwin’s book origin of species published scientists were busy in discussion with this book
- Mendel’s ideas were ahead of that time.
- Mendel used higher statistical calculation in his experiments so the results were complicated to understand.
- Mendel also performed his experiment on Heiracium plant on suggestion of karl Nageli but Mendel did not get succeed because in Heiracium parthenogenesis is present.
Reasons for Mendel’s success:
- Mendel studied the inheretance of one or two characters at a time unlike his predecessors who had considered many characters at a time (Kolreuter-Tobacco plant, John Goss &Kinght pea plant).
- Selection of material- Selection of garden pea plant is suitable for studies which have the following advantages:
(i) pea plant is annual plant with short life cycle of 2-3 month so large no of offspring can be analyzed within a short period of time.
(ii) It has many contrasting traits.
(iii) Natural self pollination is present in pea plant .
(iv) Cross pollination can be performed in it artificially so hybridization can be made possible.
(v) pea plant easy to cultivate.
(vi) pea seeds are large, In addition to pea Mendel worked on rajama.
- Mendel quantitatively analyzes the inheritance of qualitative characters.
- He maintained the statistical records of all the experiment.
Mendel’s work: Mendel studied 7 characters or 7pairs of contrasting traits.
|Actual data obtained by Mendel in F2 progenies in garden pea|
|1||Length of plant||787(tall)||277(dwarf)||2.84:1|
|3||Shape of pod||882(inflated)||299(constricted)||2.91:1|
|4||Colour of pod||428(green)||152(Yellow)||2.82:1|
|5||Shape of seed||5,474(round)||1.850(wrinkled)||2.96:1|
|6||Colour of colytedon||6,022(yellow)||2,001(green)||3.01:1|
|7||Colour of flower||705(violet)||224(white)||3.15:1|
Average of all traits studied 2.98:(=3:1)
- In pea plant sead coat colour and Flower colour are regulated by same gene.Gene which controls more than on character is called ad pleiotropic gene.
- Mendel obtained wrinkled seeds due to absence of starch Branching eazyme(SBE). In wrinkled seed free sugar is more in place of starch.
- S Blixt concluded that the genes studied by Mendel are located on four different pairs of chromosomes.
- Two of the genes are on chromosome 1st and three are on chromosome 4, genes are located far apart on the chromosome except genes controlling plant height and pod shape so Mendel did not detect linkage.
Technique of Mendel:-
He developed a technique Emasculation and bagging for hybridization in plant. Flowers of pea plant are bisexual, In this method one considered as male and another as female.
The plant used as female stamens of this plant are removed at juvenile stage this is called Emasculation. Emasculation is done to prevent self pollination. Emasculated flowers covered by bag this is called bagging. Bagging is only used to prevent undesirable cross pollination. Mature pollen grains are collected from male plants and spread over emasculated flower. Seeds are formed in the female flower after pollination. The plant that are obtained from theses seeds are called first filial generation or f1 generation according to Mendel. Mendel was great plant breeder (True breeder).