The four stages of development of genetics upto 20^th century are

Solution(By Examveda Team)

The four stages of development of genetics up to the 20^th century are Lamarckism, Weismannism, Darwinism and Mendelism.
Lamarckism, also known as Lamarckian inheritance or neo-Lamarckism, is the notion that an organism can pass on to its offspring physical characteristics that the parent organism acquired through use or disuse during its lifetime. It is also called the inheritance of acquired characteristics or more recently soft inheritance.
Weismannism's main contribution at one time also known as Weismannism, according to inheritance (in a multicellular animal) only takes place using the germ cells and the gametes such as egg cells and sperm cells.
Darwinism is a theory of biological evolution developed by the English naturalist Charles Darwin (1809 - 1882) and others, stating that all species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual's ability to compete, survive, and reproduce.
Mendelism is a term that refers to the single-gene trait's theoretical principles of heredity, which are taken from Gregor Mendel's principles, also known as Mendel's laws. Gregor Mendel conducted several experiments on pea plants for seven years and then postulated the laws of inheritance.