3.1 Chromosomes and Mechanism of inheritance.

Heredity or Inheritance:

• The transmission of genetic information from generation to generation is known as heredity or inheritance.

The mechanism of inheritance was successfully investigated before chromosomes had been observed organisms were known.

Mendel's Experiment:

• Gregor Mendel, son of the peasant farmer, was born in Moravia in 1822. Gregor Mendel first gave the accurate explanation for the mechanism of inheritance by using hybridization technique.

• Inheritance of the seven traits in garden pea plant were studied individually one at a time or in combination of two or three character at a time. He processed the data mathematically and statistically.

• Mendel postulated the principles of heredity which then became the fundamental laws of heredity, as proposed by Correns (1900).

- He visualized that the traits as such are not inherited physically but by 'something' present inside the gametic cell.

- To this 'something', he coined term 'factors' that are responsible for expression of a particular trait/ character.

- He proposed that factors are particulate in nature.

- The Mendelian factors are now termed as 'genes'.

- These factors occur in pairs in the parents and segregate from each other during gamete formation without blending/ mixing.

Seven pairs of contrasting visible characters in pea plant (Pisum sativum)

 

Reasons for Mendel's Success :

• His experiments were carefully planned and involved large sample.

• He carefully recorded the number of plants of each type and expressed his results as ratios.

• In the pea plant, contrasting characters can be easily recognized.

• The seven different characters in pea plant were controlled by a single factor each.

• The factors are located on separate chromosomes and these factors are transmitted from generation to generation.

• He introduced the concepts of dominance and recessiveness.