Genetics

             Genetics is study of science of genes, heredity and variation in living organisms. Heredity is the cause of similarity between individuals and variation is the cause of differences between individuals. Genetics deals with transmission of characters from parents to offspring and the molecular structure and function of genes. The study of genes is done at three levels.

Transmission Genetics

Population Genetics    

Molecular Genetics 

TRANSMISSION GENETICS          

The two most fundamental questions in biology are – what is the nature of genetic material and how is it transmitted from parents to offspring? The fact that living things inherit traits from their parents has been used in prehistoric times to improve crop plants and animals through selective breeding. However modern genetics only began with the work of Gregor Mendel. His breeding experiments in pea plants revealed that hereditary characteristics are determined by discrete factors (genes) that are transmitted to the next generation.

THE LAWS OF INHERTANCE

          The study of science of genetics begins with the work of Gregor Mendel. He was a clergyman and a teacher. He performed his own experiment on garden pea. He restricted his attention to the single character and kept pedigree records for each plant. Mendel studied the nature of inheritance in plants and presented his work in 1885 in the paper “Experiments on Plant Hybridisation “. The importance of his work did not get noticed until 1890s, after his death. The advantages of garden pea (Pisum sativum) as experimental system were:

The characters were readily observable.

Plants were easy to grow and self fertilise before the flowers opened

Mendel worked with 14 pure breeding varieties and selected seven pairs of characters and propounded the following laws:

The law of dominance: Mendel stated that the hereditary characters are determined by pair of factors (genes) in an individual. In a monohy--brid cross all the plants in F₁ generation showed only one character   but in F₂ the other character appears. The character in F₁ generation is dominant and the one which expresses in F₂ generation is recessive e.g., the cross between two homozygous parents (P), one with two dominant alleles for tall plant (TT) and the other with two recessive alleles for dwarf plant (tt). The phenotype of the offspring in F₂ generation is dominant and the one which expresses in F₂ generation is recessive e.g., the cross between two homozygous parents (P), one with two dominant alleles for tall plant (TT) and the other with two recessive alleles for dwarf plant (tt).  The phenotype of the offspring in F₁ generation is tall plant but the genotype is Tt.  The F₁ heterozygote produces four kinds of gametes. When this plant self-pollinates, the T and t egg and sperm cells combine randomly to form ¼TT (tall), 2/4 Tt (tall) and ¼ tt (dwarf) offspring. The F2 generation has 1:2:1 genotypic ratio and 3:1 phenotypic radio.

What is Living

What is Living :

Ø The word living cannot be defines.

Ø There are Certain characters by which can be distinguished from non-living.

1.     Growth : Increase in the number of cell or mass is called growth.

2.     Reproduction : Living organism produce young ones of their same kind.

3.     Metabolism : Chemical reaction occurring inside a living cell.

4.     Response of stimuli : Living have the ability to sense the condition of their surrounding and respond to these stimuli.

Biology

Biology :

          Branch of sciencein which living beings are studied.

Bios = Life & Logos = Study of different aspects of plants. Therefore study of life is called biology. The term biology was first coined by Lamarck and Treviranus in the year 1801. Biology has two main branch.

Ø Botany : Study of Various aspects of plants. Theophrastus is known as father of Botany.

Ø Zoology : Study of various aspects of animals. Aristotle is called father of zoology as well as biology.