Gregor Johann Mendel was born in 1822 in Silisian in a poor farmer’s family. Mendal received his early education at home and because of poverty, Mendel joined Brunn monastry at the age of 21. In 1851, he was sent to university of Vienna for study of natural sciences and mathematics. He returned to Brunn as the substitute teacher. In 1856, Mendel observed the occurrence of two types of seeds in Pea plant. Thereby he became interested in them and set out to study the effect of hybridization between different varieties. By carrying this experiment he discovered four theories or laws :-
Law of Dominance. Law of unit character. Law of Segregation .Law of independent Assortment
Mendel died in 1884 before his work came to be recognized. His work was brought into notice in 1900 by three scientists independently. They were De Vries, Tshamark and correns. They gave full credit to Mendel.
As already stated that Genetics include variations that are the differences in the character of offsprings from their parents. Variations always prevail even a monozygotic twins vary from each other. Variations are broadly classified into two form :-
Somatic (acquired) variation. Germinal variation.
SOMATIC VARIATION \This variation influence the somatic or body cells. They appear after birth and are acquired according to the need. Somatic variations are non-inheritable and usually disappear the death of an individual. They are formed due to three reasons :- environmental factors .use and disuse of organs .conscious effort
GERMINAL VARIATION :They are inheritable variation formed mostly in germinal cells which are either already present in the ancestors or develop a new due to mutations. Germinal variations are of two types :-continuous .discontinuous
Another aspect of genetics is heredity which includes the transfer of chromosomes from parents to offsprings or one generation to the next. The physical bases of heredity are genes while chemical bases of heredity is DNA. (Deoxyribo Nucleic Acid ). Each organism has a number of traits having alternate forms represented by particulate genes.Heredity depends upon chromosomes present in the nucleus of animal cell. Chromosomes are DNA complexes which constitute heredity structures because they carry coded genetic information that can be replicated transmitted and translated. DNA is the largest macromolecule made of helically twisted to anti parallel polydeoxyribonucleotide strands held together by hydrogen bonds. Each deoxyribonucleotide is formed of phosphoric acid, deoxyribose sugar and a nitrogen base. Nitrogen bases are of two types :- purines and pyrimidines. Purine of DNA are adenine and guanine while pyrimidines are cytosine and thymine. Each DNA strand has a backbone of alternate deoxyribose and phosphoric acid groups. Phosphate is connected to sugar. The complimentary nitrogen bases of the two strands are held together by hydrogen bonds – two between A and T, three between C and G.During the gamete formation the number of chromosomes is halved. So that after fertilization so formed zygote contain original number of chromosomes found in an organism. Hence serves two purposes :-Retains number of chromosomes.
i. During gamete formation segregation of chromosomes occurs independently and after fertilization crossing over occurs. Hence many new traits appear that produce variations. Hence one can say that Heredity and variation are interconnected. Heredity produce variations. Variations produce new species that gives rise to their offspring by Heredity. Genetics is a very interesting and developing field having a lot of importance. Here are a few of its importance amongst many :-It is used in Pedigree analysis to detect various inheritable diseases. It is used for improvement of human race as well as other species. It can be used to sort out cure for various genetics diseases.Genetics is a vast science that cannot be covered as such. Many scientists like Mendel and Morgan have spent their life working on it. Whole infrastructure of life is based on this. No life would have ever continued without Genetics. A quotation states that - “No one lives forever, yet the life continues”.