Notes on lesson on Genetics |



Heredity And Variation

The process of transmission of characters from one generation to another is known as inheritance or heredity.The differences that are shown by the individuals of a species and also by the offsprings of same parents are referred as variations. Variations may be harmful, useless and useful. Harmful or useless variations make individuals unfit for the struggle for existence, whereas the useful variation is quite significant and make organisms fit in nature.

Mendel's Laws of Inheritance

The following principles of Inheritance were given by Mendel- Law of dominance, the law of segregation / purity of gametes, the principle of independent assortment. He formulated these by experimenting on pea plant.


The phenomenon of permanent association of genes of a single chromosome that can be inherited in successive generations in same position and proportion without any changes or separation is called linkage. Linkage is of two types: Complete and incomplete.

Crossing Over

Crossing over is a process of exchange of genetic materials or segments between non-sister chromatids of homologous chromosomes which take place in a various mechanism.


The sudden heritable change in amount or content and organization of genetic material of organism that results in the change in appearance is called mutation. They are of various types.


The organisms having more than two sets of chromosomes by the addition of another chromosome is called polyploidy. It may arise as a result of abnormal mitosis where chromosomes divide by cytoplasm fails to divide during cytokinesis. It is of various types.

Gene Expression

Gene expression or gene regulation is the ability of a gene of an organism to express phenotype at the molecular level. Biochemically, a gene is a segment of DNA with a specific sequence of nitrogenous base. It consists of the synthesis of RNA, polypeptide, structural proteins, enzymes, and hormones that control the structure and function (metabolic activities)of specific traits.

Gene Regulation

Various terms related to gene regulations are important and discussed above. The operon model is also important and discussed above.