What is the Law of Segregation?

Mendel's Law of Segregation states that each organism has two factors (alleles) for each trait, one inherited from each parent. During the formation of gametes (sex cells), these two alleles separate — each gamete receives only one allele. This is why traits can 'skip' generations. For example, if both parents are Tt (tall), they can produce tt offspring (short) because the t alleles separate into gametes and can meet during fertilisation.

In a monohybrid cross, what is the F2 phenotypic and genotypic ratio?

In a monohybrid cross F₁ × F₁ (Tt × Tt): F₂ Phenotypic ratio = 3 Dominant : 1 Recessive (3:1). Out of 4 offspring, 3 show the dominant trait (TT + Tt + Tt) and 1 shows the recessive trait (tt). F₂ Genotypic ratio = 1 TT : 2 Tt : 1 tt (1:2:1). Remember: TT and Tt both look tall (phenotype), but their genetic makeup (genotype) is different.

What is the difference between dominant and recessive traits?

Dominant trait: appears in an organism even if only one copy of the allele is present (both TT and Tt appear tall). Denoted by capital letter (T). Recessive trait: appears ONLY when two copies of the recessive allele are present (tt). Denoted by lowercase letter (t). In Mendel's pea plant experiments: Tall (T) is dominant over Short (t); Round seeds (R) over Wrinkled (r); Yellow (Y) over Green (y). A recessive trait is 'hidden' or 'masked' in the presence of a dominant allele.

Mendel's Laws of Inheritance

Heredity and Evolution • Class 10 Science • NCERT • CBSE

Gregor Mendel discovered the laws of heredity using pea plants. Law of Segregation: each organism has two alleles for a trait; they separate during gamete formation. In a monohybrid cross (Tt × Tt), the ratio is 3:1 (dominant:recessive). Inherited traits are encoded in DNA — the genetic material.

Key Formulas

Monohybrid F₂ ratio = 3:1
Dihybrid F₂ ratio = 9:3:3:1

Frequently Asked Questions

What is the Law of Segregation?: Mendel's Law of Segregation states that each organism has two factors (alleles) for each trait, one inherited from each parent. During the formation of gametes (sex cells), these two alleles separate — each gamete receives only one allele. This is why traits can 'skip' generations. For example, if both parents are Tt (tall), they can produce tt offspring (short) because the t alleles separate into gametes and can meet during fertilisation.
In a monohybrid cross, what is the F2 phenotypic and genotypic ratio?: In a monohybrid cross F₁ × F₁ (Tt × Tt): F₂ Phenotypic ratio = 3 Dominant : 1 Recessive (3:1). Out of 4 offspring, 3 show the dominant trait (TT + Tt + Tt) and 1 shows the recessive trait (tt). F₂ Genotypic ratio = 1 TT : 2 Tt : 1 tt (1:2:1). Remember: TT and Tt both look tall (phenotype), but their genetic makeup (genotype) is different.
What is the difference between dominant and recessive traits?: Dominant trait: appears in an organism even if only one copy of the allele is present (both TT and Tt appear tall). Denoted by capital letter (T). Recessive trait: appears ONLY when two copies of the recessive allele are present (tt). Denoted by lowercase letter (t). In Mendel's pea plant experiments: Tall (T) is dominant over Short (t); Round seeds (R) over Wrinkled (r); Yellow (Y) over Green (y). A recessive trait is 'hidden' or 'masked' in the presence of a dominant allele.

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