Question

A cross between a tall plant (TT) and a short pea plant ( tt ), resulted in a progeny that were all tall plants because
A. Tallness is the dominant trait.
B. Shortness is the dominant trait.
C. Tallness is the recessive trait.
D. Height of a pea plant is not governed by gene T or t.

Answer 1

When two plants are crossed and new offspring generation plants are produced this offspring generation is called the ${F_1}$ generation or filial progeny. This process of crossing two different plants with different genotypes is called hybridization. Hybridization studies are used in the study of inheritance and genetics. Usually when two plants with different characters are crossed any one character in one of the plants is expressed in the ${F_1}$ generation.

Complete answer:
The detectable variant of an inherited character is called a trait. When two plants with different traits are hybridized to form the offspring generation usually a trait of anyone plant is expressed in the first generation. The trait expressed in the ${F_1}$ generation is called the dominant trait. The trait which was not expressed in the ${F_1}$ generation is called a recessive trait. This is Mendel’s law of dominance. Both the traits are transferred to the offspring but only one is expressed in the phenotype. Phenotype is the physical appearance of a character. A genotype is the genetic constitution of a character.
We use alphabetic letters to resemble genes. Here, T is used for the tall trait of the character ‘height of the plant’ and t to represent the dwarf trait of the character ‘height of the plant’. These are called alleles. TT and tt are the pair of alleles of the same character height. If both alleles are the same as TT, they are called homozygous. If they are different like Tt, they are heterozygous.
When the two plants with different alleles TT and tt are crossed, one allele from each parent descends to the gametes and the offspring becomes Tt in genotype. As the dominant allele T is present, the offspring will be tall in phenotype.

The correct is option (A), Tallness is the dominant trait.

Note: In the first filial generation, only the dominant character is expressed in every offspring. But in the second filial generation formed by self-pollinating the first generation offsprings, both the dominant and recessive characters are expressed in the phenotypic ratio of 3:1, where 75 percent offsprings will be tall and 25 percent offsprings will be dwarf. The genotyping ratio will be 1:2:1 where 25 percent will be homozygous tall ( TT ) 50 percent will be heterozygous tall ( Tt ) and 25 percent will be a homozygous dwarf ( tt ).