Mendel established principles that describe transmission of genes from parents to offspring. When Mendel began his studies, he knew nothing about chromosomes and role of meiosis in inheritance later investigation established parallel behaviour between chromosomes and Mendel’s unit of inheritance during meiosis. Mendel in 1856 performed his first hybridization experiment. Mendel was born in 1822 and died in 1884.
Mendel selected garden pea plant (Pisum sativum) because it showed several sharply contrasting characters that were without intermediate forms and were relatively unaffected by environmental factors. Also the flowers of garden pea are self pollinating in nature and so the crosses can be arranged according to the choice of breeder.
Mendel’s characters are:
(1) Length of Stem: tall or short
(2) Position of flowers: axial or terminal
(3) Colour of unripe pods: green or yellow
(4) Form of ripe pods inflated or constricted
(5) For of ripe seeds: round or wrinkled
(6) Colour of cotyledons: Yellow or green
(7) Colour of seed coat: Grey, brown or white.
The significance of Mendel’s work lies in his ability to formulate a scientific problem. The aim of his experiments was to study the numbers and kinds of offspring produced by hybrid individuals and to determine from the observation whether any statical relationships existed among these offsprings.
The pea plants that Mendel used in his experiments were grown from seeds obtained from plants that had ‘bred true’ when self fertilized for at least two generations before the experiment. Such plants are called true breeding. When self pollinated and self fertilized the offspring always resemble the parents for the given trait. Mendel performed corsses in which only one pair of contrasting alleles or alternative traits is being followed. Each such cross is known as monohybrid cross.
Using results of monohybrid crosses for various contrasting traits and to explain low unit factors could account for the results of monohybrid corsses.
The results Mendel’s eight years breeding experiments were read before the natural history. Society of Brunn in 1865 and in the following year these were published in the transactions of the society. But his work remained un noticed until 1990 when three distinguished botanists Hugo De Vries in Holland, Tschermak in Austria and Corrents in Germany discovered its significance. Since then Mendel’s work has formed the bosis of study of genetics. Mendel dies in 1884 before he could see his work accepted and appreciated. From the results of his experiments on carefully selected crossings, Mendel formulated certain laws to explain the interitance of characters as follows:
(1) LAW OF UNIT CHARACTERS:
This means that all characters of the plant are units by themselves being independent of one another so far as their unheritance is concerned. There are certain factors or determiners (now called genes) of unit characters, which control the expressions of these characters during the development of the plants.
(2) LAW OF DONUNANCE:
The characters are controlled by factors or genes. These occur in pairs (in chromosomes) and are responsible for tell ness and dwarfness separately. Tallness is dominant character while dwarfness is recessive character. The contrasting pairs of characters are allelomorphs. Thus tallness and dwarfness are allelomorphs.
Mendel gave two laws (1) Law of Segregation of gametes (2) Law of independent assortment.
(1) FIRST LAW OF SEGREGATION
The factors for contrasting characters remain associated in pairs in the somatic cells of each plant throughout its whole life. Later when spores are formed as a result of reduction division, the factors located in homologous chromosomes become separated out, and each of the four gamete will have only one factor (tallness or dwarfness) of the pair but not both i.e. gamete becomes pure for a particular character. This law is also called law of purity of gametes.
Mendel made experiment on Pea plants and found the ratio 3:1 in this law of segregation.
(2) SECOND LAW OF INDEPENDENT ASSORTMENT:
For dihybrid cross Mendel found that two pairs of contrasting characters are taken into idea. Mendel selected tall plant with red flower and a dwarf one with white flowers. Factors for tallness or dwarfness and red flowers or white are independently inherited and may be considered to be located in separate chromosome pairs when seeds were crossed the result became 9:3:3:1.
Mendel succeeded in formulating in his Laws of inheritance by doing experiments on plants in his garden and got good results & formed two laws. Later Mendel was considered as the father of Genetics. Later other scientists got base of Mendel’s work and enhanced in further work of Genetics.
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