Chromosomal Theory of Inheritance

Chromosomal Theory of Inheritance:

• G. J. Mendel (1865) studied the inheritance of well-defined characters of the pea plant, but it went unrecognized till 1900, for the following reasons:

1. Communication was not easy (as it is now) in those days and his work could not be widely publicised.
2. His concept of genes 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.
3. Mendel’s approach of using mathematics to explain biological phenomena was totally new and unacceptable to many of the biologists of his time.
4. 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.

• Mendel's results on the inheritance of characters were rediscovered in 1900 by three scientists named Hugo de Vries, Correns, and Von Tschermak.
• Advancements in microscopy helped scientists to carefully observe the cell division process.
• This led to the discovery of structures inside the nucleus. In eukaryotic cells, worm-shaped structures formed during cell division are called chromosomes.
• Chromosomes are filamentous bodies present in the nucleus, which are visible only during cell division.
• An organism which possesses two complete basic sets of chromosomes are known as diploid.
• A chromosome consists of a long, continuous coiled piece of DNA in which genes are arranged in linear order.
• Each gene has a definite position (locus) on a chromosome. These genes are hereditary units.
• Chromosomal theory of inheritance states that Mendelian factors (genes) have specific locus (position) on chromosomes and they carry information from one generation to the next generation.

1. Somatic cells of organisms are derived from the zygote by repeated cell division (mitosis). These consist of two identical sets of chromosomes. One set is received from female parent (maternal) and the other from the male parent (paternal). These two chromosomes constitute the homologous pair.
2. Chromosomes retain their structural uniqueness and individuality throughout the life cycle of an organism.
3. Each chromosome carries specific determiners or Mendelian factors which are now termed genes.
4. The behaviour of chromosomes during the gamete formation (meiosis) provides evidence to the fact that genes or factors are located on chromosomes.