Assertion Reason Chapter 4 Principles of Inheritance and Variation

Questions of Assertion Reason Chapter 4 Principles of Inheritance and Variation biology CBSE Class 12 are very simple to understand as this chapter deals with Principles of Inheritance and Variation means reproduction in humans which every student is very much familiar with. To solve assertion reason type questions of biology, deeper understanding of concept about Principles of Inheritance and Variation is required. In order to help the student in solving Assertion Reason type of questions, detailed process is explained.

How to solve Assertion Reason Type Questions?
In Assertion-Reason type of question, two statements are given, first is Assertion and second is called Reason. Student must have to think critically about both the statements in Assertion Reason Questions, since it combines multiple choice questions and true/false type of questions which requires a higher level of understanding.

How many types are there of Assertion Reason Type Questions?
Assertion-Reason type of questions can be asked either with four MCQ options or with five MCQ options. First four options are same in both the cases only one more options is being provided i.e. last one. One extra option increases the difficulty level of the questions.

In assertion reason type of questions, all 4 or 5 options are same for each question, which are as:

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.

Then a question haunts in every student’s mind, which option is correct and when?
This can be understood clearly with the following table:

Assertion (A)Reason (R)MCQ Options (Fixed for all questions)
If TrueTrue(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
If TrueTrue(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
If TrueFalse(c) Assertion (A) is true but reason (R) is false.
If FalseTrue(d) Assertion (A) is false but reason (R) is true.
If FalseFalse(e) Both Assertion and Reason are false.

Now, lets practice some Assertion Reason Questions of Biology Chapter : Chapter 4 Principles of Inheritance and Variation.

Read instructions carefully before answering the questions.

For question given below, two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

(a) Both A and R are true and R is correct explanation of the assertion.
(b) Both A and R are true but R is not the correct explanation of the assertion.
(c) A is true but R is false.
(d) A is false but R is true.

Assertion: Mendel was successful in his hybridization.
Reason: Garden pea proved ideal experimental material.

Ans.1. (b)
Mendel chose garden pea as plant material for his experiments, since it had the following advantages:

(i) Well defined characters.
(ii) Bisexual flowers.
(iii) Predominantly self-fertilization.
(iv) Easy hybridization.

Besides these features, garden pea, being self-fertilized, had pure lines due to natural self-fertilization for a number of years. Therefore, any variety used was pure for the characters it carried. Mendel’s success was mainly based on the fact that he considered a single character at one time.

Assertion: Mendel used true-breeding pea lines for artificial pollination experiments for his genetic studies.
Reason: For several generations, a true-breeding line shows the stable trait inheritance and expression.

Ans.2. (a)
On garden pea for many years mendel carried out hybridization experiments. He performed various types of cross breeding and then allowed the offspring for self breeding. He selected varieties and used pure lines of ture breeding lines, i.e., they produce offspring resembling the parents. these lines show the stable trait inheritance and expression for several generations making them suitable for genetic studies.

Assertion: On true breeding lines, Mendel conducted cross pollination experiments.
Reason: For several generations, true breed line have stable trait inheritance.

Ans.3. (a)
True breeding lines have inheritance of pure characters for several generations.

Assertion: Cross of F_{1} individual with recessive homozygous parent is test cross.
Reason: No recessive individual are obtained in the monohybrid test cross progeny.

Ans.4. (c)
In the monohybrid test cross progeny both heterozygous and recessive individuals are obtained in 1 : 1 ratio.

Assertion: The progeny produced have both the characters of parents.
Reason: The process by which characters pass from parent to progeny is known as inheritance.

Ans.5. (b)
According to Mendelian inheritance, genes come in different varieties called alleles. Somatic cells contain 2 alleles with one allele provided by each parent of an organism.

Assertion: The progeny in F_{2}-generation traits were identical to their parental type.
Reason: The progeny show no blending of traits.

Ans.6. (a)
Both the characters appear during the formation of F_{2}-generation, so no blending occurs.

Assertion: Genes pass from one generation to another.
Reason: The unit of inheritance are genes.

Ans.7. (b)
Chromosomes carry gene that passes on the traits of parents to the off springs during genetic recombination.

Assertion: In a monohybrid cross, F_{1} generation indicate dominant characters.
Reason: Dominance occurs only in heterozygous state.

Ans.8. (c)
Monohybrid cross is a cross between two organisms of a species which is made to study the inheritance of a single pair of alleles or factors of a character. Dominant character is one of a pair of alleles which can express itself whether present in homozygous or heterozygous state. In F_{1} , generation, the generation of hybrids produced from a cross between the genetically different homozygous individuals called parents the progenies are heterozygous dominant.

Assertion: In monohybrid cross, at F_{2} stage, both parental traits are expressed in 3: 1 proportion.
Reason: At F_{2} stage, the contrasting parental traits show blending.

Ans.9. (c)
Both the parental traits of a character in F_{2} generation are expressed in the ratio of three dominant to one recessive. Whereas, in F_{1} generation only one of the parental traits is expressed and the other lies hidden or unexpressed. However, in the hybrid there is no mixing of two characters. At the time formation of gamete, two factors separate or segregate and passes into different gametes, that hence have one factor of a pair. During fertilization, gametes fuse randomly so that factors come together in new generation and freely express themselves.

Assertion: The cross between the F_{1} progeny and either of the parent types is a test cross.
Reason: The cross between F_{1} progeny and the double recessive genotype is back cross.

Ans.10. (d)
Back cross is a cross of F_{1} hybrid with either of the two parents. When F_{1} off springs are crossed with the dominant parents, all the F_{2} generation off springs develop dominant character. On the other hand, when F_{1} hybrids are crossed with recessive parent, individuals with both the phenotypes appear in equal proportions. Crossing of F_{1} individual with dominant phenotype with its homozygous recessive parent is called test cross. It is used to determine whether the individuals exhibiting dominant characters are homozygous or heterozygous.

Assertion: A pair of contrasting characters is termed as allele.
Reason: Only one gene of an allele is expressed in an individual.

Ans.11. (c)
An allele is an alternative form of a gene one member of a pair that is located at a specific position on a specific chromosome. Diploid organisms, for example, humans, have paired homologous chromosomes in their somatic cells, and these contain two copies of each gene.

Assertion: In Mirabilis, selfing of F_{1} pink flower plants produces same phenotypic & genotypic ratio.
Reason: Flower colour gene shows incomplete dominance.

Ans.12. (a)
Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Assertion: Gametes receives only one allele of a gene.
Reason: During gamete formation, mitosis takes place leads to formation of haploid cells.

Ans.13. (c)
Meiosis is the process by which gametes are formed and during this process only one variant of gene pass to the gamete.

Assertion: In F_{2} generation of plant Mirabilis jalapa, the pink coloured flowers appear.
Reason: This is observed due epistatic suppression of white colour alleles in one of
parental flowers by red colour alleles.

Ans.14. (c)
In Mirabilis jalapa (four o’clock) have two types, of flower colour in pure state: red and white. When the two types of plants are crossed, the hybrid or plants of F_{1} generation produce pink flowers. If the latter are selfed, the plants of F_{2} generation are of three types-red, pink and white flowered in the ratio of 1 : 2 : 1. Due to incomplete dominance of red (dominant) over white (recessive), the pink colour apparently appears. Thus, pink is differentiated from red and white.

Assertion: A good example of multiple alleles is ABO blood group system.
Reason: When IA and IB alleles are present together in ABO blood group system, they both express their own types.

Ans.15. (b)
In the ABO system, consists four blood groups A, B, AB and O. ABO blood groups are controlled by gene I. The gene has three alleles IA, IB and i. This phenomenon is known as multiple allelism. IA and IB are completely dominant over i. When IA and IB are present together, they both express themselves and produce AB blood group. This phenomenon is known as codominance.

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