Genetics is a branch of biology that studies inheritance and variations. Inheritance is the process of passing characters from parents to offspring. Variation, on the other hand, is the degree by which an offspring differs from its parents.
Gregor Johann Mendel, father of Genetics, was an Augustinian priest and scientist who proposed several laws of inheritance by conducting extensive research and hybridisation experiments on garden peas for about seven years. Hybridisation is the process of crossing two individuals differing in at least one character, resulting in a hybrid individual.
The reason for Mendel choosing common pea plants for his research was that the plant had various contrasting characters such as length of the plant, colour of the pod and shape of the seed that were visible to the naked eye. Moreover, self-pollination as well as cross-pollination was possible in these plants, and crossing between these plants could be controlled.
A gene or a factor is the functional unit of heredity material. The alternative form of a gene located at a specific position on a specific chromosome is known as the allele. A trait can be defined as a distinct variant of an organism’s phenotypic character. The genetic makeup of an organism is designated by the term genotype, while the appearance of the organism is designated by the term phenotype. Every organism possesses two alleles for each character. If these two alleles for a particular character are identical, it is homozygous, and the individual is called a homozygote. On the other hand, if an organism possesses two different alleles in a pair, the gene is called heterozygous and the individual is called a heterozygote.
In a heterozygote, the gene which expresses itself in the F1 hybrid is called the dominant gene while the gene that is unable to express itself is called the recessive gene. F1 hybrid plants or animals obtained from cross-mating distinctly different parent types. When two individuals of the first filial generation are self-fertilised, the resulting progeny is F2 hybrid. Self-fertilisation is the term used when fertilisation takes place between male and female gametes from the same individual. The study of inheritance of one pair of contrasting characters is known as a monohybrid cross, while the study of inheritance of two pairs of contrasting characters is known as a dihybrid cross. To determine if an individual is homozygous dominant, heterozygous or homozygous recessive, a back cross or a test cross is carried out.