(a) Genetics is the branch of biology which deals with the study of genes, heredity and variations of inherited characters.
(b) Genes are short regions of DNA which code for either a protein or RNA molecule. It is the fundamental unit of heredity. Genes are made up of DNA strands and are found in almost every cell's nucleus.
(c) The factors responsible for rise of new species are :
(i) Natural selection : All populations respond to changes in their environment. Individuals will respond in different ways depending on their genes. Those individuals whose genes are best suited to the environment are more likely to survive and pass on their genes to the next generation. This is natural selection. Gradually, favourable genes will start to predominate in the population and less favourable genes will decline.
(ii) Genetic drift : It is caused due to drastic changes in the frequencies of particular genes by chance alone. Genetic drift with changes in the gene flow imposed by isolation mechanism acts as an agent of speciation which ultimately results in evolution.
(iii) Reproductive isolation : It is a major factor in speciation since it interrupts with geneflow.Geographical isolation is caused by various types of barriers such as mountain ranges, rivers and seas. It leads to reproductive isolation due to which there is no flow of genes between separated groups of population which ultimately results in speciation.