In a monohybrid cross, what is the phenotypic ratio observed in the F2 generation, assuming complete dominance?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• 1:1
• 3:1
• 9:3:3:1
• 1:2:1
Correct Option: B  [ 3:1 ]

Remark: For a monohybrid cross (e.g., Tt x Tt), the F2 phenotypic ratio is 3 Dominant : 1 Recessive (e.g., 3 Tall : 1 Dwarf).

If a pure tall pea plant (TT) is crossed with a pure dwarf pea plant (tt), all the F1 offspring are tall (Tt). This illustrates which of Mendel's laws?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Law of Independent Assortment
• Law of Segregation
• Law of Linkage
• Law of Dominance
Correct Option: D  [ Law of Dominance ]

Remark: The Law of Dominance states that in a heterozygous condition, the dominant allele (T) expresses itself and masks the effect of the recessive allele (t).

A test cross involves crossing an individual with an unknown genotype with a parent having which type of genotype?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Heterozygous Dominant
• Homozygous Dominant
• Homozygous Recessive
• Any F1 hybrid
Correct Option: C  [ Homozygous Recessive ]

Remark: A test cross is performed by crossing an organism with an unknown genotype with a homozygous recessive parent to determine if the unknown is homozygous dominant or heterozygous.

In a dihybrid cross involving pea plants for seed shape (Round/Wrinkled) and seed color (Yellow/Green), what is the expected phenotypic ratio in the F2 generation?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• 3:1
• 1:2:1
• 9:3:3:1
• 1:1:1:1
Correct Option: C  [ 9:3:3:1 ]

Remark: The Law of Independent Assortment dictates that the F2 phenotypic ratio of a dihybrid cross is 9 (Double Dominant) : 3 (Dominant/Recessive) : 3 (Recessive/Dominant) : 1 (Double Recessive).

What is the phenotypic outcome of a cross between a red-flowered snapdragon (RR) and a white-flowered snapdragon (rr) in the F1 generation, if the trait shows incomplete dominance?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• All red flowers
• All white flowers
• All pink flowers
• 1 Red : 1 White
Correct Option: C  [ All pink flowers ]

Remark: In incomplete dominance, the heterozygote (Rr) expresses an intermediate phenotype, resulting in pink flowers.

Human ABO blood groups are an excellent example of which non-Mendelian inheritance pattern?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Pleiotropy
• Multiple Allelism
• Co-dominance
• Both B and C
Correct Option: D  [ Both B and C ]

Remark: The ABO blood group system is governed by three alleles (IA, IB, i), showing Multiple Allelism, and IA, IB show Co-dominance in IAIB genotype.

Which genotype represents Blood Group AB in humans?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• IA IA
• IB i
• IA IB
• i i
Correct Option: C  [ IA IB ]

Remark: Blood Group AB is the result of co-dominance between the IA and IB alleles.

If a child has blood group O (ii), and the father has blood group A (IA i), what is the mother's most likely genotype, assuming she is blood group B?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• IB IB
• IA IB
• IB i
• i i
Correct Option: C  [ IB i ]

Remark: For the child to be blood group O (ii), both parents must contribute the i allele; thus, the mother must be IB i.

What is the phenotypic ratio in the F2 generation of an incomplete dominance cross (e.g., pink snapdragons × pink snapdragons)?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• 3:1
• 1:2:1
• 9:3:3:1
• 2:1
Correct Option: B  [ 1:2:1 ]

Remark: In incomplete dominance, the genotypic ratio 1:2:1 matches the phenotypic ratio (1 Red : 2 Pink : 1 White).

Linkage is the exception to which of Mendel's laws?

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Law of Dominance
• Law of Segregation
• Law of Independent Assortment
• Law of Unit Factors
Correct Option: C  [ Law of Independent Assortment ]

Remark: Linkage occurs when genes are close on the same chromosome and inherited together, violating independent assortment.