Class 12 Biology Chapter 5 Principles of Inheritance and Variation

Class 12 Biology Chapter 5 Principles of Inheritance and Variation The answer to each chapter is provided in the list so that you can easily browse through different chapters Assam Board HS 2nd Year Biology Chapter 5 Principles of Inheritance and Variation Question Answer.

Class 12 Biology Chapter 5 Principles of Inheritance and Variation

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Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 12 Biology Chapter 5 Principles of Inheritance and Variation Solutions for All Subjects, You can practice these here.

Principles of Inheritance and Variation

Chapter – 5


Very Short Answer Type Questions

Q.1. In a Mendelian cross the first hybrid generation is called ____

Ans : F₁ generation. 

Q.2. Gregor Mendel, conducted hybridization experiments on ____

Ans : Pea (Pisum sativum) 

Q.3. Heterozygous parent produces ____ kinds of gametes. 

Ans : Two.

Q.4. Genes which pair for a contrasting traits are known as ____

Ans : Heterozygous. 

Q.5. Mendelian factors are presently known as _____

Ans : Gene. 

Q.6. The physical association of two genes is termed as_____ by Morgan. 

Ans : Homologous.

Q.7. Sickle-cell anaemia is caused by ____ of Glutamic acid by ____ 

Ans : Removal, valine.

Q.8. Phenylketonuria results in mental ____ of brain. 

Ans : Retardation. 

Q.9. Turner’s syndrome results due to loss of a _____ chromosome in human females. 

Ans : Sexual/sex.

Q.10. The total number of chromosomes in a normal human cell is _____

Ans : 46 (23 pairs) 

Q.11. The XO syndrome is called _____

Ans : Turner. 

Q.12. _____ coined the term linkage. 

Ans : Morgan. 

Q.13. The genetic disorder due to additional X chromosome is ____ syndrome. 

Ans : Klinefelter’s 

(B). True or False (One Mark Each): 

Q.1. 9 : 3 : 3 : 1 is the Mendel’s dihybrid ratio. 

Ans : True. 

Q.2. The two alleles of a gene pair are located on homologous sites on the homologous chromosomes. 

Ans : True. 

Q.3. Chromosomal theory of inheritance was proposed by Hugo de Vries. 

Ans : False. 

Q.4. Female heterogamety in terms of sexchromosome is found in crow. 

Ans : True. 

Q.5. In sickle cell anemia substitution of glutamic acid by serine occurs at sixth position of a chain of haemoglobin. 

Ans : False.

Q.6. Grasshopper is an example of XO type of sex determination. 

Ans : True. 

Q.7. In pea plant the green pod colour is dominant over yellow pod colour. 

Ans : False. 

(C). Very Short Answer Questions : (One Mark Each) 

Q.1. Who rediscovered the experimental results of Mendel? 

Ans : Hugode Vrics, Correns and Tschermak. 

Q.2. What is pedigree analysis? 

Ans : It is considered as the study of transfer and distribution of certain genetic traits through past generations of men and women. By pedigree analysis we can predict the chance of occurrence of genetic diseases in 2. their children even before a woman conceives. 

Q.3. What is Mendel’s monohybrid ratio? 

Ans : Mendel’s monohybrid ratio is 3:1. 

Q.4. How many contrasting traits Mendel noted in garden pea? 

Ans : 7 pairs (seven pairs) 

Q.5. What is male heterozygosity? 

Ans : When the males have different combination of chromosomes like XO and XY, then it is called as heterozygosity. 

Q.6. Name the two main types of mutations. 

Ans : Two types of mutations are : 

(a) Chromosomal mutation. 

(b) Gene mutation or point mutation. 

Q.7. Who coined the term linkage? 

Ans : Morgan first coined the term linkage. 

Q.8. Write the genotype of man with blood group AB. 

Ans : The genotype of a man of Blood group AB is Iᴬ Iᴮ 

Q.9. What is codominance?

Ans : In case of codominance, alleles express themselves independently even when present together. 

Q.10. Which genes show very low recombination? 

Ans : Closely linked genes. 

Q.11. Who is called as the father of genetics? 

Ans : Gregor Johann Mendel. 

Q.12. What are holandric genes? 

Ans : The genes which are located in 4-chromosome and which express the male characters are called holandric genes. 

Q.13. Define point mutation. 

Ans : The mutation which occurs in gene and which causes physical or chemical change of the gene is called point mutation. 

Q.14. Name the two kinds of linkage. 

Ans : Linkages are of two types: 

(a) Complete linkage. 

(b) Incomplete linkage. 

Q.15. What is female heterozygosity? 

Ans : When the females are with two different sets of chromosomes then they are called as female heterozygosity. Heterozygous female possesses ZW and ZO chromosomes. 

Q.16. What is frame shift mutation? 

Ans : When the mutation is caused by addition or deletion of the base of DNA is called frame-shift mutation. 

Q.17. Which Mendelian disorder is known as Royal Disease? 

Ans : Haemophilia.

Q.18. What is a dominant character? 

Ans : The character which can express in F₁ generation is called dominant character. 

Q.19. What are mutagens? 

Ans : The chemicals or agents which can be used to cause mutation is called mutagen.

Q.20. What is a phenotype? 

Ans : The expressive or visible character of an organism is called the phenotypic character. 

Q.21. What is a test cross? 

Ans : A cross between F₁ hybrid (Tt) and its homozygous recessive parent (tt) is called test cross. 

Q.22. How many chromosomes a person with Turner’s syndrome has? 

Ans : Such persons are monosomic for sex chromosomes i.e. possess only one X and no Y chromosome (XO). In other words they have chromosome number 2n-1-45. 

Q.23. Define chromosome? 

Ans : Chromosome can be defined as a highly coiled DNA which is covered by chromatin substance. Chromosomes are the carrier of heredity. The chromosome number is fixed for a specific organism. For example Human being is with 46. 

Q.24. Express the genotype of AB blood group. 

Ans : The genotype of AB blood group is IᴬIᴮ. 

Q.25. Name the amino acid which is failed to convert to tyrosine during phenylketonuria. 

Ans : Phenylalanine.

(D). Short Answer Questions (Two Marks Each) : 

Q.1. Differentiate between the following. (each pair two marks. 

(a) Homozygous and Heterozygous. 

Ans :   

(i)Homozygous individuals bear  similar alleles (TT, tt)(i)Heterozygous individuals bear dissimilar alleles (Tt, Rr)
(ii)Bear either dominant or recessive alleles never both.(ii)Always with both dominant and  recessive alleles.
(iii)It produces only one type of gametes i.e. T.T, or t, t.(iii) It produces both type of gametes i.e. T and t.
(iv)They don’t exhibit extra vigour.(iv)They exhibit extra vigour.

(b) Dominant gene and recessive gene. 

Ans :           

(i)It is able to express its effect even in the presence of its contrasting allele.(i)It cannot express its effect in presence of its contrasting alleles.
(ii)It does not require the company of another similar allele for producing its effect on the phenotype.(ii)It can produce its phenotypic effect only in the company of a similar allele.

(c). Monohybrid ratio and Dihybrid ratio.  

Ans :

Mono HybridDihybrid
(i)The cross between two indiv iduals taking a single contrasting The or characters at a time.(i)The cross between two indivi duals taking two contrasting traits or character at a time.
(ii)It helps to study the inheri tance of a pair of allele.(ii)It helps to study the inheritance of two pairs of allele.
(iii)The phenotypic ratio in F₂ generation is 3 : 1.(iii)The phenotypic ratio in F₂ generation is 9: 3: 3:1.

(d) Male heterozygosity and Female heterozygosity. 

Ans :      

Male HeterozygosityFemale Heterozygosity
(i) Here males are heterozygous.(i)Here females are heterozy gous.
(ii)It involves XO and XY Type.(ii)It involves ZO and ZW type.
(iii)Absence or presence of Y chromosome helps in determi- nation of sex in males.(iii)Absence or presence of W chromosome helps is determin ation of sex is female.

(e) Sex chromosomes and Autosomes.

Ans :

Sex ChromosomesAutosomes
(i)The chromosomes which help us to determine the sex i.e. male or female is called sex chromosome.(i)The chromosome which are  found in all the cells of the  organisms is called autosomes.
(ii)They are either X or Y chromosome.(ii)There is no such division.
(iii)XX indicates for female and XY indicates male in normal condition.(iii)Except X and Y others are  autosomes.

(f) Genotype and Phenotype. 

Ans :  

(i)Genotype is the gene compl ement of an organism i.e. TT or Tt for a tall plant.(i)It is the expression of a character i.e. tall or dwarf.
(ii)Genotype remains unchanged. the influence of environment.(ii)Phenotype may change under.
(iii)It can be studied directly.(iii)It cannot be studied or observed directly.
(iv)organisms with different geno type may have similar pheno- type i.e. Tallness (phenotype) may with TT or Tt.(iv)Organisms with different phenotype is always with different genotype.

Q.2. Define linkage.

Ans : The gene located on the same chromosome may pass together as a single unit form one generation to other due to the phenomenon called likange. 

Q.3. Why did Mendel selected pea plant for his experiments? 

Ans: Mendel selected the pea plant for experiment for two reasons. 

(i) Many varieties were available with observable alternate forms for a trait/character. 

(ii) Peas are generally self-pollinated (self fertilised) and can be easily cross- pollinated when self-pollination is prevented.

Q.4. Define codominance. 

Ans : When the F₁ generation resembles both the parents, and both the parental character are expressed simultaneously, then the phenomenon is called codominance. 

Example : “AB’ type blood group is possible when allele ‘A’ and ‘B’ come together and since both the alleles are expressing their effect in F₁ generation and are therefore, codominance. 

Q.5. What is mutation? 

Ans : Mutation can be defined as a sudden change in genetic sequence of an individual which may lead to variation of characters. 

Q.5. What is Polyploidy? 

Ans : The phenomenon of failure of cytokinesis after cell division results in increase of a whole set of chromosome in an organism is called polyploidy. 

Q.6. Under which condition, does the law of independent assortment hold good and why? 

Ans : In dihybrid cross it appears that some contrasting characters which are recessive remain suppressed in F₁ generation. But during gamete formation, all contrasting characters which remained hidden in F₁ generation come out in different proportion which means the contrasting characters do not blend, rather these segregate and behave independent of each other. This is called independent assortment.

Q.8. The human male never passes on the gene for hemophilia to his son. Why? 

Ans : The human male never passes gene to his son for haemophi because it is inherited through an X linked recessive gene. The haemophilia gene (Xʰ) is always associated with X-chromosome. Therefore daughter always receives Xʰ gene from father but not his son who receives Y. chromosome from father.

Class 12 Biology Chapter 5 gene for hemophilia

Q.9. Define chromosomal theory of inheritance. 

Ans : The concept of chromosome was not given by Mendel, but he had mentioned as factor. It was found later that the ‘factors’ were the chromosome which were the carrier of heredity. Thus chromosome theory was come to light. Later it was proved that chromosomes were the carrier of heredity characters. 

Q.10. What are the Mendel’s Laws of Inheritance? 

Ans : Mendel’s laws of inheritance are: 

(a) Law of dominance. 

(b) Law of segregation.

(c) Law of independent assortment. 

Q.11. What is Filial progeny? 

Ans : In a cross between two parents, the first hybrid generation is called first filial generation or F₁ generation. Similarly subsequent generation are called F₂F₃ generation etc.

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