In a large majority of higher organisms (especially among animals), the most striking difference between the individuals of same species from the point of view of reproduction is sex. The individuals differ in their mode of producing gametes.
Some individuals produce less number of generally non motile gametes (egg) while others produce a large number of motile gametes (sperm). Thus the individuals are classified into male and female.
In a large majority of animals the male and female individuals are differentiated from each other by a number of secondary sexual characters in addition to the primary difference. Hence in animals there is generally sexual dimorphism (between male and female individuals).
ADVERTISEMENTS:
In plants however, the sexes are separate no doubt, but both the sex organs are borne on the same individual. Such individuals in which both the sexes are found on the same individual are called Hermaphrodite or monoecious.
In some of the plants (Vallisnaria), however the male and female individuals are different dioecious in that the sexes are separated on two individuals. There will be a male plant and female plant. But it has to be pointed out however that unlike in the case of animals, there are no secondary sexual characters in plants to distinguish between the individuals.
Except for sex organs, both individuals look alike. The basis of dioeciousness is one of the most interesting problems in biology. What constitutes the basis of difference between male and female individuals, is it structural or physiological or both?
What constitutes the additional differences between males and females in addition to sex? The problem of sex determination has been engaging the attention of biologists since a long time.
ADVERTISEMENTS:
Ancient scientists, philosophers etc have given their valued opinions on the subject. The following is a brief history of sex determination.