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Dominant Trait

A dominant trait is the trait that appears even when only one dominant allele is present.

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Student-friendly explanation

A dominant trait shows its effect in a heterozygous condition. This means if a dominant allele is paired with a recessive allele, the dominant trait is the one that appears in the organism. In school genetics, dominant traits are often shown with capital letters such as T for tallness.

How to write this in exams

  1. 1

    Start with the exact idea

    A dominant trait is the trait that appears even when only one dominant allele is present.

  2. 2

    Then show how to use it

    1. Identify the two alleles. 2. Check which allele is dominant. 3. See whether the genotype is heterozygous. 4. Write the trait shown by the dominant allele. 5. Mention that the recessive trait is hidden.

  3. 3

    Add one concrete example

    In pea plants, tall stem height is dominant over short stem height. A plant with genotype Tt will usually be tall.

  4. 4

    Avoid this incomplete answer

    A common wrong answer is to say the dominant trait is the one with two copies only. That is incorrect because one dominant allele can be enough to show the trait.

Definition

A dominant trait is the trait that appears even when only one dominant allele is present.

Example

In pea plants, tall stem height is dominant over short stem height. A plant with genotype Tt will usually be tall.

Rule to remember

A dominant allele expresses itself in a heterozygous condition and masks the recessive allele in the phenotype.

Memory hook

Dominant means it appears with one copy.

Examples and method

Worked example

If T stands for tall and t stands for short, then Tt is tall because the dominant T allele shows its effect. The recessive short trait is present in the genotype, but it does not appear in the phenotype.

Method to apply

1. Identify the two alleles. 2. Check which allele is dominant. 3. See whether the genotype is heterozygous. 4. Write the trait shown by the dominant allele. 5. Mention that the recessive trait is hidden.

Diagram support

A Punnett square with one capital allele and one small allele helps show why the dominant trait appears.

How CBSE asks it

State why a trait appears in Tt, or identify the visible trait in a heterozygous cross.

Avoid common mistakes

Common confusion

Students often think dominant means more common or stronger in every situation. In genetics, dominant means it shows in heterozygous form, not that it is always best.

Common wrong answer

A common wrong answer is to say the dominant trait is the one with two copies only. That is incorrect because one dominant allele can be enough to show the trait.

Exam tip

When a question gives one capital and one small letter, check which trait is dominant and then write the visible trait.

Quick check

What happens when one dominant allele and one recessive allele are present together?

The dominant trait shows up because one dominant allele is enough to express the feature. The recessive trait stays hidden in that heterozygous combination.

Study the dominant trait diagram carefully

Use the labelled diagram to keep dominant trait clear in short answers and revision.

What this diagram makes clear

This diagram keeps the labels and direction of dominant trait in the right order.

Where this helps in exams

Use this for labelled diagram work and short exam answers on dominant trait.

Revision cue

Revise dominant trait through the labels before writing the answer.

Answer writing and exam use

1-mark answer

A dominant trait is the trait that appears even when only one dominant allele is present.

2-mark answer

A dominant trait is the trait that appears even when only one dominant allele is present. A dominant allele expresses itself in a heterozygous condition and masks the recessive allele in the phenotype. In pea plants, tall stem height is dominant over short stem height. A plant with genotype Tt will usually be tall.

3-mark answer

A dominant trait shows its effect in a heterozygous condition. This means if a dominant allele is paired with a recessive allele, the dominant trait is the one that appears in the organism. In school genetics, dominant traits are often shown with capital letters such as T for tallness. A dominant allele expresses itself in a heterozygous condition and masks the recessive allele in the phenotype. If T stands for tall and t stands for short, then Tt is tall because the dominant T allele shows its effect. The recessive short trait is present in the genotype, but it does not appear in the phenotype. State why a trait appears in Tt, or identify the visible trait in a heterozygous cross. A common wrong answer is to say the dominant trait is the one with two copies only. That is incorrect because one dominant allele can be enough to show the trait.
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