Pangenes and acquired characters

Genetics : An Overview
Genetics : A study of heredity and variation
Sexuality : A source of hereditary variation
Ideas on heredity : A brief history
Ideas of Hippocrates and Aristotle
Preformation and epigenesist
Pangenes and acquired characters
Germplasm theory
Scope and significance of genetics
Transmission genetics or classical genetics
Behavioural genetics
Developmental genetics
Forward genetics vs. reverse genetics

It is pointed out earlier in this section that environmental variations have nothing to do with heredity. However, according to J.B- Lamarck (1744-1829), characters which are acquired during the lifetime of an individual are inherited. This concept is known as Lamarckism or The Theory of Inheritance of Acquired Characters. This theory was very popular in the eighteenth century to explain evolution and heredity. However, Lamarck did not point out the physical basis of this theory.

Charles Darwin (1809-1882) tried to suggest the physical basis of heredity and suggested that every part of body produced very small invisible bodies called gemmules or pangenes, which are transported through the blood stream to the sex organs and are assembled there into gametes. During fertilization, gemmules from both parents are brought together for redistribution to different organs during development, thus determining different characters. As is obvious, theory of pangenesis (pan = all; genesis = originating) proposed by Darwin is almost a copy of Lamarck's 'theory of inheritance of acquired characters' except that it suggested a physical basis. In the later part of the last century, through detailed study of cell structure and function, it was evident that Darwin's pangenesis was also based on imagination rather than on facts.

Experiments of Knight and Goss on pea Knight (1799) and Goss (1824) had conducted experiments on edible pea (Pisum sativum), much before Mendel, but failed to formulate the laws of inheritance, only because they could not give a mathematical treatment to their results. Knight was interested in improvement of fruits and vegetables and used to live in England. He crossed two varieties of pea : (i) unpigmented variety with green stem, white flowers and white seed coats and (ii) pigmented variety with purple stejpif purple flowers and grey seed coats. When unpigmented variety was pollinated by pollen from pigmented variety, only pigmented progeny appeared, which on selfing or on pollination by unpigmented variety produced both kinds of progeny in the next generation. Since he did not keep any record of number of two different kinds, he could not discover the mechanism of inheritance, and only concluded that there was a 'stronger tendency' to produce pigmented plants than unpigmented ones. Knight also noticed that the reciprocal crosses gave similar results.

Goss (1824) made similar crosses and used green seeded and yellow seeded varieties. In first generation, he got all yellow seeds and in succeeding generation derived due to selfing, he got (i) few pods with green seeds, (ii) fev pods with yellow seeds and (iii) many pods with green and yellow seeds. In the third generation he noticed that green seeds gave only green seeds, but yellow seeds gave either only yellow or yellow and green both. These results are similar to those obtained by Mendel, forty two years later (Mendel, 1866). The main reason for the failure of Knight and Goss in understanding the mechanism of inheritance, was firstly due to lack of numerical treatment of data and secondly due to their main concern for improvement of peas rather than their concern for understanding the mechanism.