NCERT Solutions for Class 12 Biology Chapter 5

Principles of Inheritance and Variation Class 12

Chapter 5 Principles of Inheritance and Variation Exercise Solutions

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Exercise : Solutions of Questions on Page Number : 93

Q1 :  

Mention the advantages of selecting pea plant for experiment by Mendel.


Answer :

Mendel selected pea plants to carry out his study on the inheritance of characters from parents to offspring.

He selected a pea plant because of the following features.

(a) Peas have many visible contrasting characters such as tall/dwarf plants, round/wrinkled seeds, green/yellow pod, purple/white flowers, etc.

(b) Peas have bisexual flowers and therefore undergo self pollination easily. Thus, pea plants produce offsprings with same traits generation after generation.

(c) In pea plants, cross pollination can be easily achieved by emasculation in which the stamen of the flower is removed without affecting the pistil.

(d) Pea plants have a short life span and produce many seeds in one generation.

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Q2 :  

Differentiate between the following -

(a) Dominance and Recessive

(b) Homozygous and Heterozygous

(c) Monohybrid and Dihybrid.


Answer :

(a) Dominance and Recessive

Dominance

Recessive

1.

A dominant factor or allele expresses itself in the presence or absence of a recessive trait.

A recessive trait is able to express itself only in the absence of a dominant trait.

2.

For example, tall plant, round seed, violet flower, etc. are dominant characters in a pea plant.

For example, dwarf plant, wrinkled seed, white flower, etc. are recessive traits in a pea plant.

(b) Homozygous and Heterozygous

Homozygous

Heterozygous

1.

It contains two similar alleles for a particular trait.

It contains two different alleles for a particular trait.

2.

Genotype for homozygous possess either dominant or recessive, but never both the alleles. For example, RR or rr

Genotype for heterozygous possess both dominant and recessive alleles. For example, Rr

3.

It produces only one type of gamete.

It produces two different kinds of gametes.

(c) Monohybrid and Dihybrid

Monohybrid

Dihybrid

1.

Monohybrid involves cross between parents, which differs in only one pair of contrasting characters.

Dihybrid involves cross between parents, which differs in two pairs of contrasting characters.

2.

For example, the cross between tall and dwarf pea plant is a monohybrid cross.

For example, the cross between pea plants having yellow wrinkled seed with those having green round seeds is a dihybrid cross.

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Q3 :  

A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?


Answer :

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Q4 :  

Explain the Law of Dominance using a monohybrid cross.


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Q5 :  

Define and design a test - cross?


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Q6 :  

Using a Punnett square, work out the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.


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Q7 :  

When a cross in made between tall plants with yellow seeds (TtYy) and tall plant with green seed (TtYy), what proportions of phenotype in the offspring could be expected to be

(a) Tall and green.

(b) Dwarf and green.


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Q8 :  

Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in F1 generation for a dihybrid cross?


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Q9 :  

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


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Q10 :  

What is pedigree analysis? Suggest how such an analysis, can be useful.


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Q11 :  

How is sex determined in human beings?


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Q12 :  

A child has blood group O. If the father has blood group A and mother

blood group B, work out the genotypes of the parents and the possible

genotypes of the other offsprings.


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Q13 :  

Explain the following terms with example

(a) Co-dominance

(b) Incomplete dominance


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Q14 :  

What is point mutation? Give one example.


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Q15 :  

Who had proposed the chromosomal theory of inheritance?


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Q16 :  

Mention any two autosomal genetic disorders with their symptoms.


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<< Previous Chapter 4 : Reproductive Health Next Chapter 6 : Molecular Basis of Inheritance >>

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