GENETICS & EVOLUTION
SUMMARY NOTES
1. INTRODUCTION TO GENETICS:
Genetics is the branch of biology that explains how traits are
passed from parents to offspring. It helps us understand why
certain traits are repeated in families and why individuals
differ. The term “Genetics” was introduced by William Bateson
(1905). The Father of Genetics is Gregor Johann Mendel
(1822–1884). Mendel’s experiments on pea plants (Pisum
sativum) laid the foundation of heredity.
, 2. IMPORTANT TERMS IN GENETICS:
Term Meaning
Gene Basic unit of heredity controlling traits.
Alleles Alternate forms of the same gene.
Genotype Genetic constitution of an organism.
Phenotype Visible physical expression of traits.
Dominant Trait Expressed even with one copy of gene.
Recessive Trait Expressed only if both alleles are recessive.
Homozygous Having identical alleles (TT or tt).
Heterozygous Having different alleles (Tt).
3. MENDEL’S LAWS OF INHERITANCE:
Law 1: Law of Dominance.
In a cross between two contrasting traits, only one (dominant)
trait appears in the F₁ generation.
Law 2: Law of Segregation.
The two alleles of a gene separate during gamete formation
and unite randomly during fertilization.
Law 3: Law of Independent Assortment.
Genes for one-of-a-kind tendencies assort independently
throughout gamete formation.
SUMMARY NOTES
1. INTRODUCTION TO GENETICS:
Genetics is the branch of biology that explains how traits are
passed from parents to offspring. It helps us understand why
certain traits are repeated in families and why individuals
differ. The term “Genetics” was introduced by William Bateson
(1905). The Father of Genetics is Gregor Johann Mendel
(1822–1884). Mendel’s experiments on pea plants (Pisum
sativum) laid the foundation of heredity.
, 2. IMPORTANT TERMS IN GENETICS:
Term Meaning
Gene Basic unit of heredity controlling traits.
Alleles Alternate forms of the same gene.
Genotype Genetic constitution of an organism.
Phenotype Visible physical expression of traits.
Dominant Trait Expressed even with one copy of gene.
Recessive Trait Expressed only if both alleles are recessive.
Homozygous Having identical alleles (TT or tt).
Heterozygous Having different alleles (Tt).
3. MENDEL’S LAWS OF INHERITANCE:
Law 1: Law of Dominance.
In a cross between two contrasting traits, only one (dominant)
trait appears in the F₁ generation.
Law 2: Law of Segregation.
The two alleles of a gene separate during gamete formation
and unite randomly during fertilization.
Law 3: Law of Independent Assortment.
Genes for one-of-a-kind tendencies assort independently
throughout gamete formation.
