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Recessive Trait

A recessive trait is the trait that appears only when both alleles are recessive.

In one line: Recessive means two copies are needed.

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Understand it

A recessive trait stays hidden when a dominant allele is present. It becomes visible only in a homozygous recessive condition, such as tt in many textbook examples. This is why recessive traits may skip a generation and then appear again when the right combination is present.

Example

In pea plants, short stem height is recessive. A plant with genotype tt will be short, while Tt will still be tall if tallness is dominant.

Rule to remember

A recessive trait is expressed only in homozygous recessive condition and is masked by a dominant allele in heterozygous condition.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1If t stands for short stem and T stands for tall stem, then tt gives short plants.
  2. 2In Tt, the dominant tall allele hides the short trait, so shortness does not appear.

Method you can reuse

  1. 1Find the recessive allele.
  2. 2Check whether both alleles are recessive.
  3. 3If yes, the recessive trait appears.
  4. 4If a dominant allele is present, the recessive trait stays hidden.
  5. 5Write the phenotype clearly.

Visual tip

A 2 × 2 Punnett square helps show that recessive traits appear only when both alleles in a pair are recessive.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

When does a recessive trait become visible in an organism?

Think first, then show answer
A recessive trait becomes visible only when both alleles are recessive. If a dominant allele is present, the dominant trait usually masks it.

Common wrong answer

A common wrong answer is to say the recessive trait appears whenever it is present in the genotype.

Why it loses marks: The dominant allele can hide it.

Don't mix this up

Students often think recessive means weak or rare in every case. That is not correct; recessive means it shows only when both alleles are recessive.

Exam tip

If the question mentions a recessive trait, check whether both alleles must be the same small letter before deciding the phenotype.

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

Identify the visible trait in a recessive condition, or explain why a recessive trait may be hidden in a heterozygote.
  1. 1

    Enough for 1 mark

    A recessive trait is the trait that appears only when both alleles are recessive.

  2. 2

    Add for 2 marks

    Example: In pea plants, short stem height is recessive. A plant with genotype tt will be short, while Tt will still be tall if tallness is dominant.

  3. 3

    Add for 3 marks

    A recessive trait stays hidden when a dominant allele is present.

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