question_answer

Write the various causes of genetic disorders in humans.

OR

Mention the salient features of Hugo de Vries theory of mutation. How do Hugo de Vries theory differs from Darwinism?

 

Answer:

Human beings suffer from various genetic disorders which occur due to:

(a) Numerical changes in chromosomes - These changes some time occur in the number of autosomes such as trisomy in the 21 chromosomes causes Down's Syndrome. Changes may occur in sex- chromosomes. Turner's Syndrome due to lack of an X-chromosome in female (44A + XO) = 45 chromosomes.

(b) By gene mutation in chromosomes - Gene mutation in sex- chromosomes causes Haemophilia, red- green colour blindness, muscular distrophy, etc. While gene mutation in autosomes causes sickle-cell anaemia, phenylketonuria, and alkaptonuria and albinism genetics disorders.

(c) Genetic disorders are also caused due to incompatibility of genes e.g., Rh- factor, blood groups, etc.

OR

According to Hugo de Vries new species arise from the pre- existing ones in a single generation by a sudden appearance of marked differences called mutations.

He believed that it is mutation which caused evolution and not the minor variations that Darwin talked about. Darwinian variations are small and directional. Evolution for Darwin is gradual while de Vries believed mutation caused speciation and hence called saltation.