Heredity is a process of transmission of traits from parents to their offspring.
Such transmissible characters are called heritable characters.
It involves the transfer of genes from parents to offsprings through asexual or sexual reproduction.
The subject that deals with the inheritance, as well as the variation of characters from parents to offspring, is Genetics.
Inheritance is the process by which characters are passed on from parent to progeny; it is the basis of heredity.
Variation is the degree by which progeny differ from their parents.
Variations can be heritable or non-heritable.
Variations are more pronounced in sexual reproduction.
Mutations provide discontinuous variations while sexual reproduction provides continuous variations.

Ancient Theories of Heredity:

Pythagoras (500 BC) proposed that every organ of the human body gives out some types of vapours. These vapours contribute to the formation of a human being.
Hippocrates (400 BC) proposed that reproductive material is handed over from all parts of the body to the developing individual.
Aristotle (300 BC) proposed that semen has some vitalizing effect. Semen was considered to be a pure form of blood and that it puts life into the inert matter provided by mother.
Leonardo Da Vinci (1452-1519) proposed that mother and father contribute equally to the heredity of the offspring.
Some scientists speculated that there is a ‘little man’ or Homunculus in the sperm.
The theory of Homunculus was published in the journal des Scavans on 7th Feb 1695.
K.F. Wolff (1738-1794) refuted the Homunculus theory. He proposed that gametes contain substances that are capable of organizing the body after fertilization.
This theory formed the basis of the Theory of Epigenesis.
Theory of Epigenesis proposed that many new organs and tissues were absent originally and have developed gradually.
Weismann in 1892 proposed the Theory of Germplasm to explain the heredity.
According to this theory, the body of an organism contains two types of cells namely somatic cells and reproductive cells.
The germ cells contain the germplasm which plays an important role in the development of the human being.
Variation can be continuous or discontinuous, as shown below: