Dominant Trait
A dominant trait is the trait that appears even when only one dominant allele is present.
In one line: Dominant means it appears with one copy.
Practice This ConceptUnderstand it
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.
Example
Rule to remember
A dominant allele expresses itself in a heterozygous condition and masks the recessive allele in the phenotype.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
- 1If T stands for tall and t stands for short, then Tt is tall because the dominant T allele shows its effect.
- 2The recessive short trait is present in the genotype, but it does not appear in the phenotype.
Method you can reuse
- 1Identify the two alleles.
- 2Check which allele is dominant.
- 3See whether the genotype is heterozygous.
- 4Write the trait shown by the dominant allele.
- 5Mention that the recessive trait is hidden.
Visual tip
A Punnett square with one capital allele and one small allele helps show why the dominant trait appears.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
What happens when one dominant allele and one recessive allele are present together?
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Common wrong answer
A common wrong answer is to say the dominant trait is the one with two copies only.
Why it loses marks: One dominant allele can be enough to show the trait.
Don't mix this up
Exam tip
Dominant Trait diagram
Open full screen to read every label clearly.
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
- 1
Enough for 1 mark
A dominant trait is the trait that appears even when only one dominant allele is present.
- 2
Add for 2 marks
Example: In pea plants, tall stem height is dominant over short stem height. A plant with genotype Tt will usually be tall.
- 3
Add for 3 marks
A dominant trait shows its effect in a heterozygous condition.
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