# Class 12 Biology MCQ – Inheritance Principles – Punnett Square-2

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This set of Class 12 Biology Chapter 5 Multiple Choice Questions & Answers (MCQs) focuses on “Inheritance Principles – Punnett Square-2”.

1. What filial generation exhibits a genotypic ratio of 1:2:1?
a) F0
b) F1
c) F2
d) F3

Explanation: The genotypic ratio refers to the ratio of different genotypes observed in a population. In the F2 generation of a Mendelian cross, the proportion of homozygous dominant: heterozygous: homozygous recessive is 1:2:1.

2. Which mathematical expression can be used to obtain the genotypic ratio of F2 offsprings from the gametes of the F1 progeny?
a) Monomial expression
b) Binomial expression
c) Trinomial expression
d) Algebraic expression

Explanation: The binomial expression (ax+by)2 can be used to model the Mendelian genetics of F2 progeny. The x and y refer to the dominant and the recessive gametes obtained from the F1 heterozygous progeny.

3. Self-crossing of dwarf plants from F2 generation will produce _____
a) 100% tall and 0% dwarf plants
b) 0% tall and 100% dwarf plants
c) 50% tall and 50% dwarf plants
d) 25% tall and 75% dwarf plants

Explanation: The F2 dwarf plants are homozygous recessive. Therefore, the self-crossing will only produce dwarf plants as no copy of the dominant allele is present.
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4. What method can be used to check the genotypic composition experimentally of the F2 tall plant?
a) Test cross
b) Self cross
c) Check cross
d) Exam cross

Explanation: To determine the genotype of a tall plant amongst the F2 progeny, Mendel employed test crossing. Here he crossed the tall plant with a recessive dwarf plant. If the genotype of the tall plant were TT, the offspring will all be tall. However, if the genotype is Tt, there will be 50% tall and 50% dwarf plants.

5. What is the genotype of a plant showing a dominant phenotype of violet flowers if it is test crossed and produces only violet-flowered plants?
a) VV
b) Vv
c) vv
d) v

Explanation: Test cross involves a cross between the plant whose genotype is to be determined with the homozygous recessive plants. If a violet-flowered plant is crossed with white-flowered plant, the offsprings will have one v allele. Thus, to exhibit a phenotype of violet-flowering, the genotype will be Vv. Hence the parent will have a genotype of VV.

6. What is the genotype of a plant showing a dominant phenotype of violet flowers if it is test crossed and produces both violet-flowered and white-flowered plants?
a) VV
b) Vv
c) vv
d) v

Explanation: If a cross occurs between violet-flowered and white-flowered plants, the offsprings will have an allele v. To have both violet and white flowers, the violet-flowered parent should be able to produce both V and v containing gametes. Thus, the genotype of the unknown parent will be Vv.

7. Mendel proposed three laws of inheritance based on his studies involving monohybrid crosses in pea plants.
a) True
b) False

Explanation: Based on his studies of monohybrid crosses, Mendel proposed two laws of inheritance. The third law came from his studies of dihybrid crosses.

8. What are the rules postulated by Mendel based on his studies of inheritance in pea plants called?
a) Principles of Inheritance
b) Rules of Inheritance
c) Principles of Heredity
d) Rules of Heredity

Explanation: Mendel formulated specific rules that he observed based on his studies in pea plants. These rules were later found to be universal and, in fact, the central pillars of genetics. These are now known as the principles or laws of inheritance.

9. What is the first law of Mendel termed as?
a) Law of Recessivity
b) Law of Dominance
c) Law of Segregation
d) Law of Independent Assortment

Explanation: The laws of inheritance were proposed by Mendel. These were verified by his experiments on pea plants and many others that followed him. The first of these laws is termed as the law of dominance.

10. What is the second law of Mendel called?
a) Law of Recessivity
b) Law of Dominance
c) Law of Segregation
d) Law of Independent Assortment

Explanation: The second law of Mendel is called the law of segregation. It gives the rule or pattern followed by the gametes during meiosis.

11. Which of the following is not a law postulated by Mendel?
a) Law of Recessivity
b) Law of Dominance
c) Law of Segregation
d) Law of Independent Assortment

Explanation: Mendel stated three laws of inheritance. These are the law of dominance, the law of segregation, and the law of independent assortment. The law of recessivity is not the law proposed by Mendel.

12. Which law explains the expression of the dominant phenotype in the F1 progeny?
a) Law of Recessivity
b) Law of Dominance
c) Law of Segregation
d) Law of Independent Assortment

Explanation: The first law of Mendel, also known as the law of dominance, explains the outcome of a monohybrid cross. It explains the reason for all progeny to have dominant phenotype as all progeny contain one copy of each allele obtained from parents, one of which is dominant over the other.

13. Which law explains the expression of the dominant phenotype in the F2 progeny?
a) Law of Recessivity
b) Law of Dominance
c) Law of Segregation
d) Law of Independent Assortment

Explanation: According to the law of dominance, the factors occur in pairs. One factor is dominant over the other. This leads to suppression of the expression of the recessive allele. Thus, the recessive allele can express only when both copies of the gene are recessive. This can give the F2 progeny the observed phenotype of 75% dominant and 25% recessive.

14. What does the second law of Mendel state?
a) Factors occur in pairs
b) The alleles separate during meiosis and pair up during fertilization
c) One factor is dominant over the other
d) Factors determine the characters of the offsprings

Explanation: The second law of Mendel is the law of segregation. It states that the alleles are segregated during the process of meiosis and these pair again after fertilization to restore the genetic composition. This explains the loss of recessive phenotype in F1 and reappearance of it in F2 generation.

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