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Rajasthan Board Class 12 (RBSE) Biology — practice by topic

Browse 176 questions across 15 Biology topics. Choose what you want to revise, then open a question to check its answer and worked solution.

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Biology topics

Reproduction In Organisms (35)Evolution (32)Biotechnology Applications (30)Reproductive Health (30)Human Health and Disease (26)Molecular Basis of Inheritance (25)Microbes in Human Welfare (23)Principles of Inheritance and Variation (23)Principles Of Inheritance (21)Sexual Reproduction in Flowering Plants (20)Human Reproduction (19)Biotechnology: Principles and Processes (9)Biomolecules (7)Reproduction (6)Biology (5)

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In Mendel's monohybrid cross of tall × dwarf pea plants, the phenotypic ratio in the F₂ generation wasRead the answer and worked solution →A tall pea plant is crossed with a dwarf plant. Half the offspring are tall and half are dwarf. The genotype of the tall parent must beRead the answer and worked solution →The genotypic ratio in the F₂ of a monohybrid cross between Tt × Tt isRead the answer and worked solution →A cross between true-breeding red (RR) and true-breeding white (rr) snapdragons gives pink F₁ plants. This pattern is best described asRead the answer and worked solution →

Worked practice questions

In Mendel's monohybrid cross of tall × dwarf pea plants, the phenotypic ratio in the F₂ generation was

  1. 1 tall : 1 dwarf
  2. all tall, no dwarf
  3. 9 tall : 7 dwarf
  4. 3 tall : 1 dwarf
Show answer and solution

Correct answer: D. 3 tall : 1 dwarf

F₁ (all Tt) self-pollinated gives F₂ with genotypes 1 TT : 2 Tt : 1 tt. Since Tt looks just like TT, the visible (phenotype) ratio is 3 tall : 1 dwarf.

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A tall pea plant is crossed with a dwarf plant. Half the offspring are tall and half are dwarf. The genotype of the tall parent must be

  1. Tt (heterozygous)
  2. TT (homozygous dominant)
  3. tt (homozygous recessive)
  4. indeterminable from the data
Show answer and solution

Correct answer: A. Tt (heterozygous)

If the tall parent were TT, all offspring of TT × tt would be Tt (tall). A 1:1 tall:dwarf ratio in the test cross means the tall parent contributed both T and t gametes — it must be Tt.

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The genotypic ratio in the F₂ of a monohybrid cross between Tt × Tt is

  1. 3 : 1
  2. 1 : 1
  3. 9 : 3 : 3 : 1
  4. 1 : 2 : 1
Show answer and solution

Correct answer: D. 1 : 2 : 1

Tt × Tt gives 1 TT : 2 Tt : 1 tt — a 1:2:1 genotypic ratio. The 3:1 figure is the **phenotype** ratio because TT and Tt both look tall.

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