Explain the law of dominance using a monohybrid cross.

1. Mendel proposed the laws of inheritance.
2. The law of dominance states that whenever the dominant allele is present, the dominant allele will express itself. The expression of the recessive allele is suppressed in the presence of dominant allele. The recessive allele does not get lost.
3. The expression remains masked in the progenies of ${F_1}^{}$ generation and reappears in the next generation.
4. When a cross is performed between two individuals taking a single contrasting character at a time, is called a monohybrid cross.
5. The character 'height' has two alleles 'T' and 't'. 'T' is for tallness, whereas 't' explains dwarfness.
6. When a pure tall (TT) pea plant is crossed with a pure dwarf (tt) plant in the $F_1$ generation hybrid, 'Tt' is obtained which is tall due to the presence of allele 'T',
7. This shows that tallness is dominant over dwarfness, which remains unexpressed in generation.
8. Diagrammatically it can be explained as:

Phenotypic ratio = 3 : 1

Genotypic ratio = 1 : 2 : 1