CBSE Class 12 Biology Principles Of Inheritance And Variation Worksheet Set A

Principles of Inheritance and Variation MCQ Questions with Answers Class 12 Biology

Question- Mendel selected pea as material for his experiments because
(a) it is an annual plant with comparatively short life cycle.
(b) the flowers are self-pollinated.
(c) the number of seeds produced is quite large.
(d) all of the above.

Answer- D

Question- Which of the following crosses would produce a genotypic ratio of 1 : 2 : 1 in F2 ?
(a) AB × AB
(b) Ab × ab
(c) Ab × Ab
(d) ab × ab

Answer- C

Question- Sickel-cell anaemia is an example of
(a) sex-linked inheritance.
(b) deficiency disease.
(c) autosomal heritable disease.
(d) infectious disease.

Answer-C

Question- The crossing of F1 to homozygous recessive parent is called
(a) back cross
(b) test cross
(c) F1 cross
(d) all of these

Answer-B

Question- In humans, the dominance relationship between the A and B alleles of the ABO blood group gene is an example of
(a) complete dominance
(b) incomplete dominance
(c) codominance
(d) epistasis

Answer-C

Question- Distance between the genes and percentage of recombination shows
(a) a direct relationship
(b) an inverse relationship
(c) a parallel relationship
(d) no relationship

Answer-A

Question- It is well known that Queen Victoria of England was a carrier for haemophilia. Since this is an X-linked disease, it can be predicted that
(a) all of her sons would have had disease.
(b) all her daugthers would have been carriers.
(c) her father must definitely have had haemophilia.
(d) haemophilia would have occurred in more of her male than her female descendents.

Answer-D

Question- Mutations can be induced with
(a) infrared radiations
(b) I AA
(c) ethylene
(d) gamma radiations

Answer-D

Question-The number of phenotypes in ABO blood groups is
(a) 1
(b) 4
(c) 6
(d) 8

Answer-B

Question- Sex is determined in human beings
(a) by ovum.
(b) at time of fertilization.
(c) 40 days after fertilization.
(d) seventh to eight week when genitals differentiate in foetus.

Answer-B

Question- Extra chromosome ‘X’ is present in which one of the following cases?
(a) Down syndrome
(b) Klinefelter syndrome
(c) Turner syndrome
(d) Bleeder’s disease

Answer-(b)

Question- The person with Turner’s syndrome has
(a) 45 autosomes and X sex chromosome
(b) 44 autosomes and XYY sex chromosomes
(c) 45 autosomes and XYY sex chromosomes
(d) 44 autosomes and X sex chromosome

Answer-(d)

Question- Punnett square is used to know the
(a) outcome of a cross
(b) probable result of a cross
(c) types of gametes
(d) result of meiosis

Answer-(b)

Question- A character which is expressed in a hybrid is called
(a) dominant
(b) recessive
(c) co-dominant
(d) epistatic

Answer-(a)

Question- The ratio of phenotypes in F2 of a monohybrid cross is
(a) 3 : 1
(b) 1 : 2 : 1
(c) 9 : 3 : 3 : 1
(d) 2 : 1

Answer-(a)

Question- ABO blood group system is due to
(a) multifactor inheritance
(b) incomplete dominance
(c) multiple allelism
(d) epistasis

Answer-(c)

Question- A pure tall pea was crossed with a pure dwarf pea. All the plants of F1 were found to be tall. This is due to
(a) law of dominance.
(b) disappearance of factor for dwarfness in F1 generation.
(c) segregation of factors.
(d) co-ordination.

Answer-(a)

Question- Which Mendelian idea is depicted by a cross in which the F1 generation resembles both the parents?
(a) Law of dominance
(b) Inheritance of one gene
(c) Co-dominance
(d) Incomplete dominance

Answer-(c)

Question- Mendel’s last law is
(a) segregation
(b) dominance
(c) independent assortment
(d) polygenic inheritance

Answer-(c)

Question- Three children in a family have blood types O, AB and B respectively. What are the genotypes of their parents?
(a) IA i and IBi
(b) IAIB and i i
(c) IBIB and IAIA
(d) IAIA and IBi

Answer-(a) 

Very Short Answer Type Questions

Question. Enlist the steps of controlled cross-pollination. Would emasculation be needed in a cucurbit plant? Give reasons for your answer.
Answer : Steps of controlled cross-pollination are
(i) Selection of parents with desired characters.
(ii) Emasculation, i.e., if the female parent bears bisexual flowers, before dehiscence anther should be removed by forceps.
(iii) Bagging, i.e., emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen.
(iv) When the stigma of bagged flower attains receptivity, mature pollen grains collected from anthers of the male parent are dusted on the stigma
(v) The flowers are rebagged and the fruits are allowed to develop.
Emasculation is not always needed in a cucurbit plant. Emasculation is essential only in case of bisexual flowers to prevent self-pollination. In case of cucurbit plant, female parent produces usually unisexual flowers but may sometimes have bisexual flowers.
Note If the female parent produces unisexual flowers, there is no need for emasculation.
The female flower buds are bagged before the flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and the flower rebagged.

Question. How are alleles of particular gene differ from each other? Explain itssignifica nce.
Answer : Alleles are polymorphs that differ in their nucleotide sequence resulting in contrasting phenotype expression. Alleles are the alternative forms of a same gene for, e.g., genes for height have two allele, one for dwarfness (t) and one for tallness (T).
Significance
(i) A character may have two or more contrasting phenotypic expression, thus resulting variation in the population.
(ii) These are used in the studies of inheritance and in understanding their behaviour.

Question. In a monohybrid cross of plants with red and white flowered plants.
Mendel got only red flowered plants. On self-pollinating these F1 plants got both red and white flowered plants in 3:1 ratio. Explain the basis of using RR and rr symbols to represent the genotype of plants of parental generation.
Answer : Phenotypic ratio Red flower : White flower 3 : 1
Genotype ratio RR : Rr : rr 1 : 2 : 1
Generally, upper case letters are used as symbols for dominant and lower case for recessive traits of the same gene (alleles). Experiment shows that it is a monohybrid cross with 3 : 1 ratio in F2-generation.
This shows parents must be true-breeds. As parents are diploid and homologous chromosomes carry alleles with similar type they are represented with RR and rr.

Question. In our society a woman is often blamed for not bearing male child. Do you think it is right? Justify.
Answer : It is unfortunate that in our society women are blamed for giving birth to female children and have been ostracised and ill-treated because of this false notion. Out of 23 pairs of chromosomes present, 22 pairs are exactly same in both males and females, these are the autosomes.
A pair of X-chromosomes are present in the female, whereas the presence of an X and Y-chromosome are determinant of the male characteristic. During spermatogenesis among
males, two types of gametes are produced. 50 per cent of the total sperm produced carry the X-chromosome and the rest 50% has Y-chromosome besides the autosomes. Females, however, produce only one type of ovum with an X-chromosome. There is an equal probability of fertilisation of the ovum with the sperm carrying either X or Y-chromosome.
In case when the ovum fertilises with a sperm carrying X-chromosome the zygote develops into a female (XX) and the fertilisation of ovum with Y-chromosome carrying sperm results
into a male offspring. Thus, it is evident that it is the genetic makeup of the sperm (male) that determines the sex of the child.
It is also evident that in each pregnancy there is always 50% probability of having either a male or a female child.

Question. Discuss the genetic basis of wrinkled phenotype of pea seed.
Answer : Seed shape is determined by a single gene, with the allele (R) for round peas dominant over the allele (r) for wrinkled peas (recessive trait).
It the alleles for the gene controlling the seed shape are homozygous in a plant, it will show the character or phenotype of same alleles, i.e.,-RR- round seed, rr-wrinkled seed.
On the other hand, if the alleles of gene are heterozygous. They will express the phenotype of dominant allele.
Rr - Round seed (r- wrinkled is recessive) This is the genetic basis of wrinkled phenotype of pea seed.

Question. Even if a character shows multiple allelism, an individual will only have two alleles for that character. Why?
Answer : Multiple alleles are the multiple forms of a gene which occur on the same gene locus, but distributed in different organisms in the gene pool with an organism, which carry only two alleles and the gamete have only one allele. Despite multiple allelism, an individual will have only two alleles because an individual develops from a zygote which is the result of fusion of sperm (carrying father set of (n)haploid chromosomes) and an egg (carrying mother set of haploid chromosomes). Sperm and an egg have only one gene (allele) for each trait. A zygote when becomes diploid, have two alleles for each trait. It is the maximum number of alleles an individual can have. e.g., genes of blood groups.

Question. How does a mutagen induce mutation? Explain with example.
Answer : Mutagens may be physical, i.e., ionising radiations X-ray,UV rays, gamma rays, DNA reactive chemicals, i.e., hydroxyl radicals, H O 2 2, etc., or biological such as virus.
A mutagen can induce mutation by inducing, a change in the base sequence by insertion, deletion or substitution.
e.g., a single base sequence substitution at the sixth codon of the b-globin gene changes the codon from GAG to GUG. This results in the substitution of glutamic acid (Glu) by valine
(Val) at the sixth position of the b-globin chain of the haemoglobin molecule. The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in the shape of the RBC from biconcave disc to the elongated sickle, i e . ., like structure which is not functional.

Short Answer Type Questions

Question. How was it concluded that genes are located on chromosomes?
Answer : Chromosome theory of inheritance was proposed by Sutton and Boveri independently in 1902. The theory believes that chromosomes are vehicles of heriditary information,
possess Mendelian factors or genes and it is the chromosomes which segregate and assort independently during transmission from one generation to the next.

Question. A plant with red flowers was crossed with another plant with yellow flowers. If F1 showed all flowers orange in colour, explain the inheritance.
Answer : Incomplete dominance is the phenomenon where neither of the two alleles shows dominance thus producing intermediate hybrid between the expression of two alleles in homozygous state. In this case, a new phenotype in between the two original phenotype appears.  (Image 94)

Question. Why is the frequency of red-green colourblindness is many times higher in males than that in the females?
Answer : Colourblindness is a X-inked sex inheritance. For becoming colourblind, the female must have the allele for it in both her X-chromosomes and if only one X-chromosome of female possess allele for colour blind character she becomes the carrier for this characteristics But males develop colourblindness when their sole X- chromosome has the allele for it.
Thus males are more prone to colour blindness while females are carriers.

Question. How do genes and chromosomes share similarity from the point of view of genetical studies?
Answer : By 1902, the chromosome movement during meiosis had been worked out.
Walter Sutton and Theodore Boveri, (1902) noted that the behaviour of chromosomes was parallel to the behaviour of genes and used chromosome movement to explain Mendel’s Laws.
They studied the behaviour of chromosomes during mitosis (equational division) and during meiosis (reduction division). The chromosomes as well as genes occur in pairs and the two
alleles of a gene pair are located of homologous sites of homologous chromosomes. Chromosome movement in meiosis and germ cell formation in a cell with four chromosomes. Chromosomes segregate when germ cells are formed.

Question. What is recombination? Discuss the applications of recombination from the point of view of genetic engineering.
Answer : Recombination refers to the generation of new combination of genes which is different from the parental types. It is produced due to crossing over that occurs during meiosis prior to gamete formation.
Applications of Recombination
(i) It is a means of introducing new combinations of genes and hence new traits.
(ii) It increases variability which is useful for natural selection and under changed environment.
(iii) Since, the frequency of crossing over depends upon the distance between the two genes, the phenomenon is used for preparing linkage chromosome maps.
(iv) It has proved that genes lie in a linear fashion in the chromosome.
(v) Breeders have to select small or large population for obtaining the required cross-overs.
For obtaining cross-overs between closely linked genes, a very large population is required.
(vi) Useful recombinations produced by crossing over are picked up by breeders to produce useful new varieties of crop plants and animals. Green revolution has been achieved in India due to this selective picking up of useful recombinations. Operation flood or white revolution is also being carried out on the similar lines.

Question. What is artificial selection? Do you think it affects the process of natural selection? How?
Answer : Artificial selection (or selective breeding) describes intentional breeding for certain traits or combination of traits by humans, for exploiting the variations existing among species. It is of three types-mass selection, pure-line selection and clonal selection.
Yes, it affects the process of natural selection. Natural selection selects for/or against traits based on their effect on the fitness of the organism. In artificial selection, traits are selected based on human preference for improving traits.
The process of natural selection leads to evolutionary change in the expression of the trait in the population, whereas the artificial selection, though being the same process, involves the traits preferred by humans for its own benefit. It is a much faster process than the natural selection but it may impose threat on diversity in long run making it unfit to the environment.

Question. With the help of an example differntiate between incomplete dominance and co-dominance.
Answer : Incomplete dominance is a phenomenon where two contrasting alleles are present together but neither of the alleles is dominant over other and the phenotype formed is intermediate of the two alleles.
e.g., the kind of inheritance in the dog flower (Snapdragon or Antirrhinum species) in which the intermediate trait is expressed in F1-generation.
Codominance is a phenomenon in which when two contrasting alleles are present together  and both of the alleles express themselves.
e.g., AB blood group in humans where both the alleles are expressed to produce RBC surface antigens A and B.

Question. It is said, that the harmful alleles get eliminated from population over a period of time, yet sickle-cell anaemia is persisting in human population. Why?
Answer : Sickle-cell anaemia is an autosomal recessive disease caused by haemoglobins an oxygen carrying protein in blood cells.
Despite the disease’s lethal symptoms, it protects the carrier from malaria. Its allele are most common in the people of African descent (about 7% people of African descent carry an allele) and some other are as where malaria in prevalent.
It provides the vital protection from malaria. Individuals with HbAS heterozygotes tend to survive better than individuals with HbSS (homozygotes) as they are not exposed to the same severity of risk.

More Question

1. Define heredity, genetics, and inheritance.

2. Why did Mendel select pea plant for his experiments?

3. How did Mendel make sure that the pea plants were true breeding?

4. List the traits in garden pea plant which Mendel studied in his breeding experiments.

5. What is emasculation technique?

6. Define the following terms:

(i) Allele                        (ii) homozygous

(iii) Heterozygous          (iv) Dominant gene

(v) Recessive gene        (vi) Genotype

(vii) Phenotype

7. (a) What is monohybrid cross? How did Mendel carry out this cross? Show with help of Punnet square.

(b) Explain Law of Dominance.

(c) Explain Law of Segregation of gametes.

8. What kind of gametes would be produced by the organisms having the following genotypes?

(i) AaBB

(ii) aaBB

(iii) Aabb

(iv) AaBBCc

9. In human beings, blue eye colour is recessive to brown eye colour. A brown-eyed man has a blueeyed mother.

(a) What is the genotype of the man and his mother?

(b) What are the possible genotypes of his father?

(c) If a man marries a blue-eyed woman, what are the possible genotypes of their offspring?

10. What is test cross? Give its use.

11. In dogs black coat colour is dominant over white. What coloured dog will you choose to breed a given black dog to find its genotype? What is this type of cross known as?

12 (a) What is incomplete dominance? Describe one example of incomplete dominance.

(b) What is the difference between dominance and incomplete dominance?

13. What is multiple allelism? Give its suitable example.

14. What is codominance? Give suitable example.

15. How is codominance different from incomplete dominance?

16 (a) Describe briefly the dihydrid cross conducted by Mendel.

(b) State the Law of Independent Assortment.

17. State the reasons for which the published work for Mendel remained unrecognized for several years.

18. Who proposed the chromosome theory of inheritance? Give the salient features of this theory.

19. Why did Morgan select Drosophilia for his experiments?

20. What is linkage? Describe briefly the two types of linkage.

21. State the relationship between linkage and crossing over.

22. Briefly mention the contribution of T.H.Morgan in genetics.

23. What is the role of Henking in discovery of X-chromosome?

24. What are autosomes and sex chromosomes?

25. discuss briefly different types of sex determination

(a) XO-XX type      (b) XX-XY type     (c) ZW-ZZ type

26. What is male heterogamety and female heterogamety?

27. Define mutation and mutagens.

28. What is point mutation and chromosomal mutations?

29. What is pedigree analysis? What are the symbols used in such an analysis?

30. Give the use of pedigree analysis.

31. What is haemophilia? Why do generally only human males suffer from haemophilia? Can women also suffer? Explain

32. How is sickle cell anaemia caused? What are its symptoms?

33. Write short note on Phenylketouria.

34. What is aneuploidy? Differentiate between trisomic and haploid condition.