Question

Explain the following:
(i) Lamarckism
(ii) Sex-linked characters

Answer 1

(i) Lamarckism

Lamarckism (or Lamarckian inheritance) is the hypothesis that an organism can pass on characteristics that it has acquired during its lifetime to its offspring.

The propositions of Lamarckism are as follows:

a) In every animal which has not passed the limit of its development, a more frequent and continuous use of any organ gradually strengthens, develops and enlarges that organ.

b) New organs are formed in the body of organisms in response to a new need. For example, in the evolution of the horse, the plantigrade type of foot changed to unguligrade foot.

c) If an organ is used continuously and constantly, it tends to be highly developed, whereas misuse results in degeneration. For example, the long neck of the giraffe developed due to constant stretching to reach food.

d) Changes acquired during the lifetime of an individual are inherited by its offspring.

(ii) Sex-linked characters

An observable character of an organism controlled by the chromosome that determines the organism's sex is called as sex-linked characters.

In humans, for example, the X or female-determining chromosome carries many genes, whereas the Y or male-determining chromosome is deficient in genes. A woman has two X chromosomes; a man has one X chromosome and one Y chromosome. Colour blindness and Haemophilia are the two main sex-linked or X-linked disease are found in man.