The NCERT Exemplar Solutions Class 12 Biology Chapter 5, Principles of Inheritance and Variation, helps students in understanding how characteristics are inherited by one generation from another. The chapter starts with Mendel's experiments on pea plants by using laws of inheritance such as the Law of Dominance, the Law of Segregation, and the Law of Independent Assortment. The NCERT Exemplar Solutions allow students to build a strong foundation in the subject, making it easier for them to solve different types of questions with confidence and perform well in both school and competitive exams such as NEET.
Students can check the results of the supplementary exams for Class 10 and Class 12 on the official portal, cbse.gov.in. The compartment exams for Class 10 were conducted from July 15 - July 22, and those for Class 12 were conducted on July 15 itself.
The NCERT Exemplar Class 12 Solutions provide answers in a detailed and clear language so that students can understand the concepts without any further help. The Principles of Inheritance and Variation chapter also introduces genetic diseases such as haemophilia, sickle cell anaemia, and colour blindness, and autosomal versus sex-linked inheritance. Topics like chromosomal theory of inheritance, gene interaction, mutations, genetic recombination, and variations are included in this chapter. The NCERT Exemplar Class 12 Biology Solutions, consist of a rdifferent types of question such as MCQs, long and short answers, and diagram-based questions that allow students to revise and prepare efficiently.
NCERT Exemplar Class 12 Biology Solutions Chapter 5
The chapter Principles of Inheritance and Variation helps students learn how characters are passed from one generation to the next and also explains important ideas like Mendel’s experiments, genes, and how variations happen. The questions are present in many formats like MCQs, short and long answers. Practicing these helps students understand the concepts clearly and prepare well for exams.
Get NCERT Exemplar for Class 12 Science Chapter 5(MCQs)
Question:1
All genes located on the same chromosome: a. Form different groups depending upon their relative distance b. Form one linkage group c. Will not be from any linkage groups d. Form interactive groups that affect the phenotype
Answer:
The answer is the option (b) Form one linkage group Explanation: Closer genes are more likely to form linkages, as the linkage is decided by the vicinity of two genes. Morgan showed that genes form one linkage group when they are located on the same chromosome. Thus, (b) is the answer.
The answer is the option (a) Aneuploidy Explanation: Aneuploidy is the condition in which loss or gain of chromosomes is observed due to the failure of the separation of chromatids during the cycle of cell division. Hence, (a) is the correct option
The answer is the option (b) An inverse relationship Explanation: Reduced distance between genes increases the probability of recombination which shows an inverse relationship. Hence, (b) is the correct option.
The answer is the option (d) Sex-linked recessive Explanation: Here, the X-chromosome has the flawed gene, but the carriers of the disease are females and it is manifested in males. Thus, it is referred to as a sex-linked recessive disease. One example of such a disease is Haemophilia which is known as X-linked recessive disease.
The answer is the option (d) G U G Explanation: At the sixth codon of the beta-globin gene, single base substitution takes place from GAG to GUG. Due to this, in the globin protein, replacement of glutamic acid with valine is seen. Hence, GUG is the code for valine.
The answer is the option (b) Co-dominance Explanation: Most commonly found in ABO blood grouping, co-dominance is when the F1 generation resembles both parents. Here, the result is AB group because both A and B sugars are dominant.
The answer is the option (d) Peacock Explanation: Sex determination of the type ZZZW is observed in birds. Males have ZZ combination and females have ZW combination.
The answer is the option (b) Tt and Tt Explanation: In the case of Tt and Tt (option (b)), a few of the offspring will be dwarf (TT, Tt, tt) and most of them are going to be tall (TT, Tt). In case of option (a) and (c), the offspring will be all tall and in option (d), one of the parents is dwarf. Hence, (b) is the correct option.
Question:9
In a dihybrid cross, if you get 9:3:3:1 ratio it denotes that: a. The alleles of two genes are interacting with each other b. It is a multigenic inheritance c. It is a case of multiple allelism d. The alleles of two genes are segregating independently
Answer:
The answer is the option (d) The alleles of two genes are segregating independently. Explanation: A 9:3:3:1 ratio is the result of a dihybrid cross when two genes assort independently during gamete formation, as explained by Mendel’s law of independent assortment.
The answer is the option (c) Linkage Explanation: Whenever two genes are in close proximity and located on same chromosome, linkage takes place irrespective of the variation.
The answer is the option (a) Non-homologous chromosomes Explanation: Mendel's law of independent assortment applies when genes are located on different (non-homologous) chromosomes, allowing them to assort independently during gamete formation.
The answer is the option (a) Males and females, respectively Explanation: Males have single X-chromosomes while females have pairs of X-chromosomes. This is XO sex determination which is seen in such insects. Hence, (a) is the answer.
The answer is the option (b) Mendelian trait Explanation: Pedigree analysis can be used to trace the Mendelian disorders and the pattern of their inheritance.
The answer is the option (b) observations that the offspring of a cross, made between the plants having two contrasting characters shows only one character without any blending. Explanation: It was observed by Mendel that when two pairs of varying characters are analyzed during dihybrid cross, the behavior of a particular character is independent of another character. Hence, the correct answer is (b).
The answer is the option (a) 1:1:1:1 Explanation: Since genes A and B are linked, but a test cross is performed with a double recessive parent, the four types of gametes (parental and recombinant) are produced in equal proportion, giving a 1:1:1:1 ratio.
The answer is the option (d) Phenotypes – 4; genotypes - 9 Explanation: For example, consider a dihybrid cross between wrinkled green (rryy) and round yellow (RRYY). The phenotypes were as follows: round green, round yellow, wrinkled green and wrinkled yellow and the genotypes were: rryy, rrYy, rrYY, Rryy, RrYy, RrYY, RRyy, RRYy, and RRYY. Hence, the correct option is (d).
The answer is option (c) Both mother and father are heterozygous for the ‘A’ and ‘B’ blood groups, respectively Explanation: Offspring ii (O blood group) is the feasible phenotype of parents and IAi (A blood group) and IBi (B blood group) are the feasible genotype of the parents.
Discover NCERT Exemplar for Class 12 Science Chapter 5 (Very Short Answer Questions)
A test cross is a name for the cross between the homozygous recessive parent and the F1 progeny. The phenotype in F1 generation is determined by analysis of progenies of a test cross.
Yes, the results would have been completely different if the characters chosen were located on the same chromosome. In his experiments on Drosophila, Morgan found that the ratio of phenotype in the F1 generation was different than that in Mendel’s observation because the characters were on the same chromosome.
The breeding between parents is shown in the first row, and the number of progenies is depicted by the second row. The figure shows two female and three male children with one girl and one boy affected by some kind of genetic disease. From the figure, it can be concluded that the nature of the trait is recessive, and autosome linked in nature.
To prevent the masking of the effect of inheritance to F2 generation by character set, Mendel self-pollinated the tall F1 plants. This is because all plants of the F1 generation turned out to be tall and he could not understand the fate of the recessive character.
The fact that genes are responsible for inheritance was discovered after the discovery of chromosomes. Before that, genes were not in the knowledge of the scientists. Only after Mendel’s period, it was known that the information on the expression of a particular trait is contained in the genes.
Alleles are genes which code for a pair of contrasting characters, and these are different from each other within a pair. However, the slight difference is not noticeable as characters or phenotype, but as the absence or presence of a molecule of a substance like sugar polymer. The substance is present on the gene I which regulates the ABO blood grouping. Alleles are vital because they help in identifying whether a particular trait is recessive or dominant or even co-dominant (in some cases).
The usage of particular alphabets is only meant for convenience. Generally, the character is shown by the first letter of a particular trait, and a different case of the same letter is used to show the contrasting character. Conventionally, a capital letter depicts the dominant trait, and a lowercase letter depicts the recessive trait.
Genes carry the potentiality for the expression of a trait, i.e. phenotype and are responsible for inheritance. Phenotype depends on many factors. If a trait gets combined with a dominant one, it may get recessive, and the survival depends on the natural selection passage. Therefore, the opportunity for expression of a particular trait is provided by and depends on the environment.
The Y chromosome, which is present in males, determines the sex of the human child. Hence, it is evident that the father is responsible for having a male or a female child. Therefore, a mother should not at all be blamed for the same. However, the probability of X or Y chromosome, making its way to the zygote is equal, i.e. 50-50. Hence, no one is to be blamed or rewarded for that. A female child is as important as a male child.
Generally, seeds dry before dispersal and germination. The amount of starch in the seed decides whether the seed will be round or wrinkled, and the relative amount of starch is looked after by a gene. If there is less than the required starch in the seed, it will be wrinkled. In pea plants, a mutant gene’s enzymes are responsible for reducing the amount of starch in seeds and hence, the seeds become wrinkled.
Alleles are present only in pairs because maximum organisms are diploid. Thus, an individual will have only two alleles for the character even after showing multiple alleles. For example, the ABO blood grouping is governed by alleles I, IA and IB.
The mutation is induced by physical and chemical factors called mutagens. During replication, the base-pair sequence in the DNA is altered for inducing mutation.
Access NCERT Exemplar Class 12 Science Chapter 5(Short Answer Questions)
The alleles segregate and go to each of the parents when plants of F1 generation reproduce without the cross. The segregation is random with equal probability of a particular allele going to either of the parental gametes. Thus, genotype and phenotype in the F2 generation are identical. So, there will be 50% of plants with pure genotype and 50% of plants with mixed genotype.
Yes, it is possible for a child to have blood group O if the parents have blood group A and B. If genotypes of the parents are IAi and IBi, then gametes can have one of the genotype from i, IA or IB. The child’s genotype will be ii if fertilization of gametes occurs with i and hence the child will have blood group O.
First discovered and described by Langdon Down in 1866, Down’s syndrome refers to the presence of an additional copy of 21st chromosome. It is a chromosomal disorder. A person with this condition has:
distinct facial appearance with partially opened mouth and furrowed tongue
small round head
delayed physical and mental development
short stature
broad palm
According to studies, with advancing maternal age, the chances of Down’s syndrome increase in the child. This is because cells get older with the age of the mother and the ova are present since birth in females. Various physio-chemical exposures also lead to increased chances.
The behaviour of chromosome and genes was studied during meiosis by Walter Sutton and Theodor Boveri, and they observed similar movement in chromosome and gene. Hence, it was proposed by them that genes are located on chromosomes.
Incomplete dominance of a particular trait over another is seen sometimes which results in the manifestation of both characters in some way. For example, consider genotype of red flowers to be RR and that of yellow flowers to be rr. In F1 generation, all progenies have genotype as Rr. Hence, orange flowers are produced by all plants in F1 generation because red colour does not completely dominate the yellow colour.
The genes with photo-pigments are located on X-chromosome, and if the gene is destroyed or missing, it results in colour blindness. Chances of this disease are much higher in males than in females because males have only one X-chromosome; hence there is no second X-chromosome to compensate for the defect, like in females. Females have colour blindness if the defect is in both her X-chromosomes.
X-chromosome contains the genes for colour blindness. However, in the male child, the X-chromosome is contributed by the mother. Therefore, the son inherits the trait from the mother even if his father is suffering from colour blindness.
Recombination is a combination of genes which is different from parental gene combination. It can occur either naturally during meiosis or artificially through genetic engineering, which is used for recombining different species for producing beneficial products for humans. For example, production of BT cotton, BT brinjal, and vaccines like hepatitis B was done with genetic engineering.
The selective breeding of animals and plants is called artificial selection. It is done to include advantageous traits in plants and animals, and it can be natural or artificial. However, ethically, artificial selection is wrong. But according to the law of survival of the fittest, only the varieties which are fit to survive will survive in artificial selection. Therefore, it will not affect the process of natural selection.
A single pair of alleles, i.e. HbA and HbS, controls the sickle cell anaemia. The offspring may suffer from this disease if both parents are heterozygous (HbAHbS). But the offspring should be homozygous (HbSHbS) because heterozygous carry this disease. However, it persists in humans because, in adaptation, heterozygous individuals are advantageous.
Know the NCERT Exemplar Class 12 Science Chapter 5 (Long Answer Questions)
The cross between a dwarf plant with white flowers (ttrr) and a tall plant with red flowers (TTRR) is depicted by the Punnett Square shown below:
Plants of the F1 generation will produce red flowers and will be tall. When they are permitted to self-pollinate, F2 generation’s phenotype can be depicted by following Punnett Square. Here, the ratio is 9:3:3:1, which is the standard dihybrid ratio, also shown as:
Tall plant red flower = 9
Tall plant white flower = 3
Dwarf plant red flower = 3
Dwarf plant white flower = 1
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This ratio stands true only when the contrasting characters have their genes on distinct chromosomes. This is because of the fact that there will be interaction if the characters are on the same chromosome.
1. In humans, males are called heterogametic because they have X and Y chromosomes in their 23rd pair of chromosomes. On the other hand, females are called homogametic as they have two chromosomes, i.e. XX chromosomes in their 23rd pair of chromosomes. However, in birds, the scenario is quite the opposite. Male birds have ZZ chromosomes and female birds have ZW chromosomes. Hence, in cases like these, males are homogametic, and females are heterogametic. 2. The sex of an unborn child is determined by the 23rd pair of chromosomes in humans. The males have X and Y chromosomes and females have X and X chromosomes in that pair. So, when the ovum is fertilized with the sperm containing the X chromosome, the result is a female child, and when it is fertilized with the Y chromosome, the result is a male child. In some animals like crocodiles, the sex is determined by temperature. Male crocodiles are born if eggs are brooded at high temperatures.
The pedigree analysis shown below depicts the colour blindness in offspring:
The F1 generation depicts two female children and one male child – One of the female children might be a carrier, and the male child will suffer from colour blindness.
The P generation depicts a normal husband and a carrier wife.
About 8% of the males are colour blind, while only 0.5% of the females are colour blind. This is because only one X-chromosome is present in males. If that one X chromosome carries the defect, the boy will suffer from colour blindness. But in females, there are two X chromosomes which help in the compensation of deficiency in one of the chromosomes. Thus, females are generally carriers of the disease and rarely the sufferer.
Sturtevant was one of the students of Morgan. Morgan has carried out several experiments related to genetics. Some of their contributions are:
In the various dihybrid crosses of Drosophila carried out by Morgan, it was observed by him that the phenotypic ratio did not resemble the standard ratio, which was observed by Mendel. Morgan and his group noticed that the genes did not show independent segregation when they were located on the same chromosome as they were aware that genes were located on the X chromosome. Morgan termed the interaction of genes on the same chromosome as linkage and the generation of non-parental combination as recombination. On the same chromosome, the probability of parental combination is much higher than that of non-parental combination.
Sturtevant discovered that on the same chromosome, recombination or lack of recombination was largely dependent on the relative distance between the two genes. There was no recombination when genes were tightly linked, and chances of recombination were higher when genes had a large distance between them.
Contributions made by Morgan and his group, including Sturtevant, contributed hugely to the development of the genetic mapping.
Aneuploidy is a condition in which gain or loss of chromosome is seen during the cell division due to the failure of chromatid segregation. On the other hand, an increase in the number of chromosome set caused due to the failure of cytokinesis after telophase is called polyploidy. This condition is mostly seen in plants and rarely seen in animals.
Trisomy of 21st chromosome: First discovered and described by Langdon Down in 1866, it refers to the presence of an additional copy of 21st chromosome. It is known as Down’s syndrome. A person with this condition has a distinct facial appearance with partially opened mouth and small round head. Physical and mental development is delayed in such individuals.
XXY: In this condition, a karyotype of 47 is caused due to an additional copy of the X chromosome. It is a genetic disorder and is called Klinefelter’s syndrome. In this case, three chromosomes (XXY) are present in the 23rd set of chromosomes. A person suffering from this disorder is sterile and has enlarged breasts (gynecomastia) with overall masculine development.
XO: Lack of an X chromosome causes this genetic disorder of ploidy of 45 (XO). It is known as Turner’s syndrome. Such females have rudimentary ovaries and are sterile. The absence of secondary sexual characters is also seen.
Approach to Solve Questions of Class 12 Biology Chapter 5
This chapter consists of a mix of direct, conceptual, and application questions. To answer the questions effectively in the chapter Principles of Inheritance and Variation students can follow the steps given below
Read the NCERT textbook and Exemplar thoroughly to grasp Mendel's experiments, inheritance laws (dominance, segregation, independent assortment), and deviations such as incomplete dominance and linkage.
Practice in drawing and labelling Punnett squares for monohybrid and dihybrid crosses, and diagrams illustrating chromosomal sex determination.
Learn key words such as gene, allele, homozygous, heterozygous, genotype, phenotype, linkage, recombination, and mutation.
Complete all exemplar questions, concentrating on key areas such as Mendelian ratios, blood group inheritance, genetic disorders (such as haemophilia, sickle cell anaemia, and Down's syndrome), and chromosomal basis of inheritance.
The experiments and works of scientists such as Gregor Mendel (inheritance laws), Sutton and Boveri (chromosomal inheritance theory), and Thomas Hunt Morgan (linkage and recombination) need to read thoroughly.
Most Important topics in Class 12 Biology Chapter 5
This chapter explains how traits are passed from one generation to the next and why variations occur among individuals. Given below are the important topics from the Principles of Inheritance and Variation chapter.
Principles of Inheritance and Variation is a key chapter for NEET and board examinations that describes how characteristics and traits are inherited from one generation to the next. It is centred on the basic genetic laws identified by Mendel and branches out into more detailed patterns of inheritance.
Question 1: Which of the following is an example of incomplete dominance?
A) A cross between red and white snapdragon flowers producing pink flowers B) Human blood group AB expresses both A and B antigens C) Height in humans shows continuous variation D) Sickle cell anaemia affecting multiple traits
Answer: The correct answer is option (A) A cross between red and white snapdragon flowers producing pink flowers
Explanation: Incomplete dominance occurs when neither allele is completely dominant, resulting in a heterozygous phenotype that is intermediate between the two parents. In snapdragons, crossing red (RR) and white (rr) flowers produces pink (Rr) flowers, demonstrating incomplete dominance.
1.What is a linkage group and how are genes on the same chromosome inherited?
A linkage group is a set of genes located on the same chromosome that tend to be inherited together. All genes on the same chromosome form one linkage group, which corresponds to the number of chromosomes in the organism.
2.What is aneuploidy and how does it arise?
Aneuploidy refers to the condition where an organism has one or more extra or missing chromosomes (e.g., 2n+1, 2n–1). It arises due to the non-disjunction of chromosomes during cell division, leading to the gain or loss of chromosomes.
3.How is the distance between genes related to recombination frequency?
The distance between genes on a chromosome shows a direct relationship with the percentage of recombination. The further apart two genes are, the higher the chance of recombination between them during meiosis.
4.Why is solving NCERT Exemplar problems important for this chapter?
Solving NCERT Exemplar problems helps students understand a variety of question types, including MCQs, match the following, Punnett square problems, and conceptual questions. This practice strengthens conceptual understanding and prepares students for board and competitive exams like NEET.
5.What types of questions are included in the NCERT Exemplar for this chapter?
The exemplar includes multiple-choice questions, very short answers, short answers, long answers, and fill-in-the-blanks. These cover both fundamental concepts and higher-order thinking skills, ensuring comprehensive exam preparation.
Changing from the
CBSE board
to the Odisha CHSE in Class 12 is generally difficult and often not ideal due to differences in syllabi and examination structures. Most boards, including
Odisha CHSE
, do not recommend switching in the final year of schooling. It is crucial to consult both CBSE and Odisha CHSE authorities for specific policies, but making such a change earlier is advisable to prevent academic complications.
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A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is
