Four different gametes are produced by a dihybrid plant and on selfing, it yield 16 offsprings.

Dihybrid test cross and the ratio is 1 : 1 : 1 : 1

(a) Dihybrid cross ratio = 9 : 3 : 3 : 1
(b) Dihybrid test cross ratio = 1 : 1 : 1 : 1

When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent to the other pair of characters. Genes that are located in different chromosomes assort independently during meiosis.

It is crossing an individual of unknown genotype with a homozygous recessive. (Tt \(\times\) tt) or YyRr \(\times\) YYrr.

(a) Phenotypic ratio = 3 : 1
(b) Genotypic ratio = 1 : 2 : 1

The term genotype is the genetic constitution of an individual. The term phenotype refers to the observable characteristic of an organism.

i) The Law of Dominance,
ii) The Law of Segregation

Emasculation: Removal of anthers from the flower
Alleles: Alternate forms of a gene

Seed shape, flower color, flower position & pod color.

Gregor Mendel selected seven pairs of characters in Pisum sativum (garden pea)

Mendel's theory of inheritance, known as the Particulate theory, establishes the existence of minute particles or hereditary units or factors, which are now called as genes.

Heredity - Transmission of characters from parents to off springs.
Variations - organisms belonging to the same natural population or species that shows a difference in the characteristics.

(a) Classical genetics
(b) Molecular genetics
(c) Population genetic
(d) Quantitative genetics

"Genetics" is the branch of biological science which deals with the mechanism of transmission of characters from parents to offsprings. The term Genetics was introduced by W. Bateson in 1906.