A trait that is always expressed during crossing of hereditary characteristics is

1. Analyze the question The question asks which trait is always expressed when hereditary characteristics are crossed. In other words, which trait shows up in the offspring's phenotype whenever its allele is present?

2. Explain the concept In Mendelian genetics, each trait is controlled by a pair of alleles, one from each parent.

• A dominant allele is expressed whenever it is present, whether the genotype is homozygous (TT) or heterozygous (Tt).
• A recessive allele is expressed only when two copies are present (tt). It is masked in heterozygotes.
• Homozygous and heterozygous describe the genotype (whether the two alleles are the same or different). They are not traits that are expressed.

3. Step-by-step solution

• Take a cross between a tall plant (TT) and a short plant (tt). All F1 offspring are Tt and all are tall. The tall trait is expressed and the short trait is hidden.
• Option A (recessive): it is masked in heterozygotes, so it is not always expressed.
• Option B (dominant): it is expressed whenever the allele is present, so it is always expressed.
• Option C (homozygous): this is a genetic makeup, and a homozygous recessive individual (tt) still shows the recessive trait, so it does not tell us which trait is expressed.
• Option D (heterozygous): this is also a genetic makeup, and it does not decide which trait appears.

4. Answer The correct option is B. dominant trait.

5. Exam tip Remember: Dominant = Displayed. If even one dominant allele is present, the dominant trait shows. The recessive trait needs two copies to appear. Also, "homozygous" and "heterozygous" describe genotype, so they are rarely the answer when the question asks about an expressed trait.