Important Terms

Genetics is the branch of biology that deals with the study of heredity and variation.
The characters that are being passed from one generation to the other called hereditary charters.
Variation may be defined as the difference in characteristics shown by the individual of a species and also by the offspring or sibling of the same parents.

Terms

Gene is the inherited factor that determines the biological character of an organism. A pair of contrasting characters are called allelomorph or allele.
The dominant allele is one of the factors of an allelic pair that can express itself, whether present in the homozygous or heterozygous state. E.g., T (tallness in pea), R (round seed in pea).
The recessive allele is the factor of an allele pair that is unable to express its effect in the presence of its heterozygote. E.g., t (a dwarf in pea).
In homozygous conditions, organisms have two similar genes or alleles for a particular in a homologous pair of the chromosome.
An organism containing two different alleles or an individual containing both dominant and recessive alleles of a gene is called a heterozygous condition. When only one allelic pair is considered in cross-breeding is called a monohybrid cross. When two allelic pairs are considered in a cross, it is called dihybrid.
The genotype is the sum total of heredity, or genetic makeup and phenotype is the external feature of an organism.