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NCERT Solutions for Class 12 Biology Chapter 5
Principles of Inheritance and Variation Class 12
Chapter 5 Principles of Inheritance and Variation Exercise Solutions
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.
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 A recessive trait is able to express itself only in
presence or absence of a recessive trait. the absence of a dominant trait.
2. For example, tall plant, round seed, violet flower, For example, dwarf plant, wrinkled seed, white
etc. are dominant characters in a pea plant. flower, etc. are recessive traits in a pea plant.
(b) Homozygous and Heterozygous
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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 Genotype for heterozygous possess both
recessive, but never both the alleles. For example, RR dominant and recessive alleles. For example
or rr 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, Dihybrid involves cross between parents, which
which differs in only one pair of contrasting differs in two pairs of contrasting characters.
characters.
2. For example, the cross between tall and For example, the cross between pea plants having
dwarf pea plant is a monohybrid cross. yellow wrinkled seed with those having green round
seeds is a dihybrid cross.
Q3 :
A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?
Answer :
Locus is a fixed position on a chromosome, which is occupied by a single or more genes. Heterozygous organisms
contain different alleles for an allelic pair. Hence, a diploid organism, which is heterozygous at four loci, will have four
different contrasting characters at four different loci.
For example, if an organism is heterozygous at four loci with four characters, say Aa, Bb, Cc, Dd, then during
meiosis, it will segregate to form 8 separate gametes.
If the genes are not linked, then the diploid organism will produce 16 different gametes. However, if the genes are
linked, the gametes will reduce their number as the genes might be linked and the linked genes will be inherited
together during the process of meiosis.
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NCERT Solutions for Class 12 Biology Chapter 5
Principles of Inheritance and Variation Class 12
Chapter 5 Principles of Inheritance and Variation Exercise Solutions
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.
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 A recessive trait is able to express itself only in
presence or absence of a recessive trait. the absence of a dominant trait.
2. For example, tall plant, round seed, violet flower, For example, dwarf plant, wrinkled seed, white
etc. are dominant characters in a pea plant. flower, etc. are recessive traits in a pea plant.
(b) Homozygous and Heterozygous
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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 Genotype for heterozygous possess both
recessive, but never both the alleles. For example, RR dominant and recessive alleles. For example
or rr 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, Dihybrid involves cross between parents, which
which differs in only one pair of contrasting differs in two pairs of contrasting characters.
characters.
2. For example, the cross between tall and For example, the cross between pea plants having
dwarf pea plant is a monohybrid cross. yellow wrinkled seed with those having green round
seeds is a dihybrid cross.
Q3 :
A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?
Answer :
Locus is a fixed position on a chromosome, which is occupied by a single or more genes. Heterozygous organisms
contain different alleles for an allelic pair. Hence, a diploid organism, which is heterozygous at four loci, will have four
different contrasting characters at four different loci.
For example, if an organism is heterozygous at four loci with four characters, say Aa, Bb, Cc, Dd, then during
meiosis, it will segregate to form 8 separate gametes.
If the genes are not linked, then the diploid organism will produce 16 different gametes. However, if the genes are
linked, the gametes will reduce their number as the genes might be linked and the linked genes will be inherited
together during the process of meiosis.
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