CHROMOSOMAL BASIS OF INHERITANCE

In heredity, genes are transmitted from parents to the off springs. Certain principles of genetics are followed in this. Genes are located on chromosomes. So, the genetic material is transmitted from one generation to the other by chromosomes. This is inheritance on the basis of chromosomes. Sometimes genes present on same chromosome do not assort independently but remain linked together and pass on to next generation together. This is linkage. (1.1) PARALLELISM BETWEEN GENES AND CHROMOSOMES:- There is a perfect parallelism between genes & chromosomes which can be indicated by following facts:- 1 - Each species has a specific number of chromosomes in its somatic cell. In diploid cell, chromosomes occur in pairs (homologous pairs), one member of pair comes from paternal and other comes from maternal parent. Similarly genes also occur in pairs (Allelomorphic pair); genes in pair are contributed by both parents. 2 - During mitosis, the two chromatids of a chromosome separate into 2 daughter nuclei which later form 2 daughter cells. Similarly, each gene of allelomorphic pair goes into each daughter cell 3 - AT meiosis, chromosomes of each kind (homologous chromosome) separate. Similarly, genes of each kind also separate in meiosis 4 - Chromosomes unite & form a diploid pair after fertilization. Similarly, genes also form a pair after fertilization.

Inheritance

There are different life forms which may be similar at cellular level of organization but at organismal level, a lot of diversity can be seen. Members of a particular species resemble closely & have a set of similar characters by which they are identified. Genetics deals with the study of these characters how these are passed on from one generation to another (ie, parents to offsprings) (1.1) Inheritance: Heredity and Variation Genetics (GK. 'genesis'-descent) is the branch of biology that deals with the study of heredity and variations. The term 'Genetics' was coined by William Bateson in 1906. Offspring resemble their parents. This resemblances might not be 100% which means that difference among the members of a species can also be seen. These differences shown by individual of a species and also by offspring of same parent are called 'VARIATIONS'. The transmission of characters, resemblances and variations, from one generation to the next is called Heredity.