In a plant, a tall variety was crossed with a dwarf variety. All F₁ plants were tall. When F₁xF₁ plants were interbred, 9/16 of the F₂ were tall and 7/16 were dwarf. Explain the inheritance of height by indicating the number of gene pairs involved and by designating which genotypes yield tall and which yield dwarf. (Use dashes where appropriate.)

Key Concepts

Mendelian Inheritance

Mendelian inheritance refers to the principles of heredity established by Gregor Mendel, which include the concepts of dominant and recessive traits. In this case, the tall variety is dominant over the dwarf variety, meaning that the presence of at least one dominant allele results in a tall phenotype. This principle helps explain the observed ratios in the offspring.

Gene Pairs and Alleles

In this scenario, height in plants is determined by a pair of alleles, where 'T' represents the tall allele and 't' represents the dwarf allele. The genotypes can be TT (homozygous tall), Tt (heterozygous tall), or tt (homozygous dwarf). The combination of these alleles in the F₂ generation leads to the phenotypic ratio observed.

Phenotypic Ratios

The phenotypic ratio in the F₂ generation (9 tall to 7 dwarf) suggests a more complex inheritance pattern than simple dominance, indicating the involvement of two gene pairs. This ratio can be derived from a dihybrid cross, where the tall phenotype can arise from multiple combinations of alleles, leading to the observed distribution of traits in the offspring.