Question

Explain briefly the phenomenon of inheritance by Preformation theory.

Answer 1

Preformation Theory :

• Leonardo da vinci (1452-1519) revealed the fact that the male and female parents contribute equally to the heredity of the offspring.
• W.Harvey (1651) speculated that all living things (including man) originate from eggs and that the se men only plays vitalizing role.
• It was R. de Graaf (1641-1673) who observed that the progeny would possess the characteristics of both parents (i.e., mother and father) and therefore, suggested that both the parents should contribute to heredity (biparental inheritance).
• The sperms of man and other mammals were observed first of all by A.V. Leeuwen hock in 1677.
• The mammalian egg was discovered by Von Baer in 1828. N. Grew (1682) first of all reported the reproductive organs of plants.
• With the discovery of eggs and sperms, the biologists of 17th century started to speculate that the new individual was completely preformed in miniature in the gamete.
• According to different workers such miniature preformed embryo was speculated to occur either in the egg or sperm.
• Swammerdam (1637-1680), for example, thought that a tiny preformed frog occurred in the animal hemisphere of the frog egg and that became simply larger by feeding on the food stored in the vegetal hemisphere of the egg.
• Another biologist, Hartsoeker (1695) published a figure showing a miniature man known as mankin or homunculus in the head of the human spermatazoa.
• Such preformation theories had been supported by Leeuwenhoek (1632-1723), Malpighi (1673), Reaumur, Bonnet (1720-1793), Spallanzani (1729-1799) and other workers of 17th and early 18th centuries.
• With the development of improved microscopy and other cytological techniques in 17th and 18th centuries, it became clear to biologists that neither the egg nor the sperm contained a preformed individual but that each was a relatively uniform, homogeneous mass of protoplasm.
  

Preformation Theory:

• Preformation Theory  states that as a result of an unfolding and growth of preformed parts, the generation of offspring occurs.
• It was a theory of embryological development used in the late seventeenth century through the late eighteenth century.