Principles of Inheritance and Variation

Previous Years' CBSE Board Questions

4.1 Mendel's Laws of Inheritance

VSA (1 mark)

Character Dominant Recessive (d)

1. (b) Pod shape Inflated Constricted
2. Stem height Tall Dwarf

1. A geneticist interested in studying variations and patterns of inheritance in living beings prefers to choose organisms for experiments with shorter life cycle. Provide a reason. (Delhi 2015)

2 Mention any two contrasting traits with respect to seeds in pea plant that were studied by Mendel.

(AI 2014)

4.2 Inheritance of One Gene

MCQ

1. Assertion (A): In a monohybrid cross between tall

plants and dwarf plants, the F2 generation showed Mother Father Child

tall and dwarf plants in the ratio of 3:1. (a) PP pp Pp

Reason (R): There is no blending of traits/characters (b) Pp pp pp

in the F₂ generation. (c) Pp Pp. pp

1. pp PP Pp (Term I, 2021-22) (Ap

1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true and (R) is not the correct explanation of (A).
3. (A) is true, but (R) is false.
4. (A) is false, but (R) is true. (2023) U

1. The number of different types of gametes that would or yellow (g). What percentage of offsprings with green pod colour trait would be obtained in a cross of <math>Gg \times Gg</math>?
2. 25% (b) 50% (c) 75% (d) 90% (Term I, 2021-22) [Gr]

(Al 2017)

13. State a difference between a gene and an allele.

(Delhi 2016)

1. A child with blood group O has father with blood group A and mother with blood group B. What would be the possible genotypes of parents and the child? Choose the correct option.

Father Mother Child

1. <math>I^B i</math> M Pi
2. Pi <math>I^{B}i</math> II
3. IAIA <math>I_BI_B</math> II
4. IBIB. IAIA Pi

(NCERT Exemplar, Term I, 2021-22) [Ap]

1. Given below are the pairs of contrasting traits in Pisum sativum as studied by Mendel. Select the incorrectly mentioned option from the table given below.

How many types of gametes can be produced in a

diploid organism which is heterozygous for 3 loci?

1. 4 (b) 8 (c) 16 (d) 32 (NCERT, Term I, 2021-22) (Ap)

Polydactyly (six-fingered hands) is a genetic condition

due to a dominant allele (P) over recessive allele (p). If

a six-fingered woman and a five-fingered man have a

five-fingered child, the genotype of the parents and

the child would be

V5A (1 mark)

British geneticist R.C. Punnett developed a

graphical representation of a genetic cross called

"Punnett Square". Mention the possible result this

representation predicts of the genetic cross carried.

(Delhi 2019)

Name the type of cross that would help to find the

genotype of a pea plant bearing violet flowers.

How many kinds of phenotypes would you expect in

F₂ generation in a monohybrid cross exhibiting co-

dominance? (Delhi 2014C)

SA (2 marks)

By using Punnett square depict the genotypes and

phenotypes of test crosses (where green pod colour

(G) is dominant over yellow pod colour (g) in garden

pea with unknown genotype. (2023) Ap

Two children one with blood group 'AB' and other

with blood group 'O' are born to parents where the

father has blood group 'A' and the mother has blood

group 'B'. Work out a cross to show how is it possible?

(NCERT, 2020) U

Mendel did not explain the expression of incomplete dominance in plants. Give an example of flower exhibiting incomplete dominance. Name and state the Law of Mendel the genes which exhibit incomplete dominance follow. (2020 C)

1. When does a geneticist need to carry a test cross? How is it carried? (Foreign 2015)

State and explain the law of segregation as proposed by Mendel in a monohybrid cross.

(2/5, Foreign 2015)

1. A cross was carried out between two pea plants showing the contrasting traits of height of the plants. The result of the cross showed 50% parental characters.
2. Work out the cross with the help of a Punnett square.
3. Name the type of the cross carried out. (Delhi 2014)

How does the gene 'I' control ABO blood groups in humans? Write the effect the gene has on the structure of red blood cells. (Delhi 2014)

1. In snapdragon a cross between true-breeding red flowered (RR) plants and true-breeding white flowered (rr) plants showed a progeny of plants with all pink flowers.
2. The appearance of pink flowers is not known as blending. Why?
3. What is this phenomenon known as?

(AI 2014)

1. 1:2:1
2. 3:1 Mention what does each ratio suggest. (2019)

With the help of one example, explain the phenomena of co-dominance and multiple allelism in human population. (AI 2014)

SA II (3 marks)

1. Explain Mendel's "Law of segregation" in a typical monohybrid cross with the help of a suitable example. (2020) R

Differentiate between dominance, incomplete dominance and co-dominance with the help of a suitable example of each. (2020)

Explain the phenomena of dominance, multiple allelism and co-dominance taking human ABO blood group as an example. (Al 2019)

1. What is a test cross? How can it decipher the heterozygosity of a plant? (AI 2016)

A teacher wants his/her students to find the genotype of pea plants bearing purple coloured flowers in their school garden. Name and explain the cross that will make it possible. (Delhi 2015)

1. During a monohybrid cross involving a tall pea plant with a dwarf pea plant, the offspring populations

were tall and dwarf in equal ratio. Work out a cross

to show how it is possible. (Al 2015)

1. The F₂ progeny of a monohybrid cross showed phenotypic and genotypic ratio as 1:2:1, unlike that of Mendel's monohybrid F2 ratio. With the help of a suitable example, work out a cross and explain how it is possible. (Al 2015)
2. (a) Write the conclusions Mendel arrived at on dominance of traits on the basis of monohybrid crosses that he carried out in pea plants.
3. Explain why a recessive allele is unable to express itself in a heterozygous state.

(Foreign 2014)

LA (5 marks)

1. It is sometimes observed that the F₁ progeny has a phenotype that does not resemble either of the two parents and has intermediate phenotype. Explain by taking a suitable example and working out the cross upto F, progeny. (2023) [An
2. Differentiate between incomplete dominance and co-dominance. Substantiate your answer with one example of each. (NCERT Exemplar, Delhi 2019)
3. (a) How would you find out whether a given tall garden pea plant is homozygous or heterozygous? Substantiate your answer with the help of Punnett squares.
4. Given below are the F₂ phenotypic ratios of two independently carried monohybrid crosses:
5. (a) State and explain the law of dominance as proposed by Mendel.
6. How would phenotypes of monohybrid F₁ and F₂ progeny showing incomplete dominance in snapdragon and co-dominance in human blood group be different from Mendelian monohybrid F₁ and F₂ progeny? Explain.

(NCERT, Foreign 2015)

1. (a) A couple with blood groups 'A' and 'B' respectively have a child with blood group 'O'. Work out a cross to show how it is possible and the probable blood groups that can be expected in their other offspring.
2. Explain the genetic basis of blood groups in human population. (AI 2015C)
3. Work out a monohybrid cross upto F2 generation between two pea plants and two Antirrhinum plants both having contrasting traits with respect to colour of flower. Comment on the pattern of inheritance in the crosses carried above. (AI 2014C)