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# Heredity and Genetics ## Definitions - **Trait or characteristic:** It is the recognizable feature in a person, like the height of a plant or skin color in humans. - **Clone:** A group of organisms formed by inheriting all its parental characters is known as a clone, for example, a clone of bacte...

# Heredity and Genetics ## Definitions - **Trait or characteristic:** It is the recognizable feature in a person, like the height of a plant or skin color in humans. - **Clone:** A group of organisms formed by inheriting all its parental characters is known as a clone, for example, a clone of bacteria - **Alleles or allelomorphs:** A pair of genes controls two alternative characters; they are called alleles. For example, in a cross between a tall plant and a dwarf plant, 'T' stands for the gene of tallness, and 't' stands for the gene of dwarfness. - **Homozygous:** A condition when a diploid organism has the same allelic forms of a gene, e.g., 'tt' or 'TT' is homozygous. - **Heterozygous:** A condition when a diploid organism has different allelic forms of a gene, e.g., 'Tt' is heterozygous. - **Genotype:** It is the genetic expression of an organism. It cannot be seen or observed physically. - **Phenotype:** It is the physical or observable expression of an organism. It is the result of the genotype. - **Dominant characters:** The allele that expresses itself in the F1 generation in a cross between two contrasting characters is called a dominant character. It is represented by capital letters, e.g., 'T', 'R' for tallness and red color of a flower, respectively. - **Recessive characters:** The allele which cannot express itself when present along with the dominant allele is called a recessive character. It is represented by small letters, for example, 't', 'r' for dwarfness and white color of a flower, respectively. The characteristic is expressed only when the recessive allele is homozygous. - **F1 generation:** It refers to the first filial generation. The offspring produced by crossing true-breeding parental forms are called F1 generations. - **F2 generations:** It refers to the second filial generation produced by the self crossing of the F1 generation. - **Punnet square:** It is a checkerboard, which helps to study all the possible results of various crosses. - **Monohybrid cross:** It is the cross between one pair of contrasting characters; for example, the cross between tall plants and dwarf plants. - **Dihybrid cross:** It is the cross between two pairs of contrasting characters. For example, a cross between tall plants having red flowers with dwarf plants having white flowers. - **Hybrid:** The organism which has a heterozygous condition in its genotype or the organism having different genotypes and phenotypes is called a hybrid. *** Created by CDC, Nepal JBD New Creative Science & Technology Class - 10 ***