. Explain Chromosomal Theory of Inheritance
Chromosomal Theory of Inheritance:
1. Mendel published his work on inheritance of characters in 1865 but for several reasons, it remained unrecognised till 1900.
2. Firstly, communication was not easy (as it is now) in those days and his work could not be widely publicised.
3. Secondly, his concept of genes (or factors, in Mendel’s words) as stable and discrete units that controlled the expression of traits and, of the pair of alleles which did not ‘blend’with each other, was not accepted by his contemporaries as an explanation for the apparently continuous variation seen in nature.
4. Thirdly, Mendel’s approach of using mathematics to explain biological phenomena was totally new and unacceptable to many of the biologists of his time.
5. Finally, though Mendel’s work suggested that factors (genes) were discrete units, he could not provide any physical proof for the existence of factors or say what they were made of.
6. In 1900, three Scientists (de Vries, Correns and Von Tschermak) independently rediscovered Mendel’s results on the inheritance ofcharacters. Also, by this time due to advancements in microscopy thatwere taking place, scientists were able to carefully observe cell division.This led to the discovery of structures in the nucleus that appeared to double and divide just before each cell division. These were called chromosomes (colored bodies, as they were visualised by staining).
7. By 1902, the chromosome movement during meiosis had been worked out. Walter Sutton and Theodore Boveri noted that the behaviour of chromosomes was parallel to the behaviour of genes and used chromosome movement to explain Mendel’s laws.
8. Recall the behaviour of chromosomes during mitosis (equational division) and during meiosis (reduction division). The important things to remember are that chromosomes as well as genes occur in pairs. The two alleles of a gene pair are located on homologous sites on homologous chromosomes.