NCERT Solutions Chapter 4 Class 12 Principles of Inheritance and Variations

 Exercises 

1. Mention the advantages of selecting pea plants for experiment by Mendal.

Ans :  Gregor Mendal selected pea plants ( Pisum sativum ) for his experiments because they had several advantages .

Advantages of using pea plants :

A) Easy to grow and maintain : Pea plants can be grown easily in gardens or pots without special care.

B) Short life cycle : They grow, flower, and produce seeds quickly, allowing observation of multiple generations in a short time.

C) Clear and contrasting traits :

Pea plants show easily distinguishable characteristics (like tall vs dwarf, yellow vs green seeds), making results simple to analyze.

D) Self-pollinating nature :

They naturally self-pollinate, which helps maintain pure lines (true-breeding plants).

E) Artificial cross-pollination possible :

Mendel could easily control breeding by manually transferring pollen from one plant to another.

F) Large number of offspring :

Each plant produces many seeds, giving reliable statistical data.

These features made pea plants ideal for studying inheritance patterns and helped Mendel establish the basic laws of genetics.

2. Differentiate between the following :

a) Dominance and Recessive 
b) Homozygous and Heterozygous 
c) Monohybrid and Dihybrid.

Ans : a) Dominance  : i)  Expresses itself in both homozygous (TT) and heterozygous (Tt) conditions.
ii) Masks the recessive trait in heterozygous condition.
iii) Represented by a capital letter (T).
Example: Tallness in pea plants.

Recessive : i) Trait that expresses only when both alleles are homozygous  (tt).
ii) Gets masked by dominant trait in heterozygous condition.
iii) Represented by a small letter (t).
Example: Dwarfness in pea plants.

b) Homozygous : i) It contains two identical alleles (TT or tt).
ii) It is called pure condition.
iii) It shows only one type of trait (either dominant or recessive).
Example: TT (tall) or tt (dwarf) in pea plants.

Heterozygous :  i) It contains two different alleles (Tt).
ii) It is called hybrid condition.
iii) It shows dominant trait only (recessive is hidden).
Example: Tt (tall) in pea plants.

c) Monohybrid : i) Involves only one trait.
ii) Example: Height (Tall × Dwarf).
iii) Produces 2 types of gametes.
iv) F₂ phenotypic ratio = 3 : 1.
v) Simple and easy to study

Dihybrid : i) Involves two traits at the same time.
ii) Example: Height and seed color.
iii) Produces 4 types of gametes.
iv) F₂ phenotypic ratio = 9 : 3 : 3 : 1.
v) More complex than monohybrid.

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

Ans : We know that,

Number of gamete types = 2ⁿ

(where n = number of heterozygous loci)

Here,

n = 4, then number of gamet types = 2^4 = 16

Answer:

👉 16 types of gametes can be produced.