This document explains key genetic concepts, including definitions of genes, alleles, genotypes, and phenotypes, alongside their roles in heredity and expression. It describes the structure of DNA, including the significance of promoters, exons, introns, and codons in gene transcription and translation. Various genetic terms such as 'genetics,' 'genome,' and the types of alleles are also discussed.

1. GENES
Dr. P. Saranraj M.Sc., M.Phil., Ph.D., NET
Assistant Professor
Department of Microbiology
Sacred Heart College (Autonomous)
Tirupattur, Vellore District.
Mobile: 9994146964
E.mail: microsaranraj@gmail.com

2.  Gene is a locus or region of DNA that encode a
functional RNA or Protein product and molecular unit
of heredity.
 The term “Gene” was first coined by Wilhem
Johannensen in 1909.
 “Genetics” is the study of genes, heredity and
genetic variations in living organisms.
 The term “Genetics” was first proposed by the English
biologist William Bateson (1861 - 1926) in 1909.
 “Genome” is a complete copy of the entire set of
DNA, including all of its genes.

3.  “Allele” refers to “A specific variation of a
gene” (Example - Blue eyes, Green eyes, Type
A blood, Black skin and White skin).
 “Allele” also refers to “Different forms of
characteristics”.
 “Allele” are also called as Allelomorphs
 There are two types of Alleles. They are:
1) Homozygous Alleles – Two same alleles
2) Heterozygous Alleles – Two different alleles

4. Genotype Phenotype
Definition The genetic makeup
of an individual.
Refers to the
information
contained on two
alleles in the cell.
Detectable expression
of the genotype. An
expressed and
observable trait.
Examples DNA and
Susceptibility to
diseases
Hair colour, Eye
colour, Weight and
other physical
characters
Inheritance Inherited from
parents to young
ones
Cannot be inherited

5. Genotype Phenotype
Depends upon The hereditary
information that was
given to an individual
by their parents
Genotype and the
influence of the
environment
Contains All the hereditary
information of an
individual, even if
those genes are not
expressed.
Expressed genes only
Determined by Genotyping – using a
biological assay, such
as PCR, to find out
what genes are on an
allele. (Inside the body)
Observation of the
individual (Outside the
body)

8.  Promoter
Promoter is a region of DNA that initiates
the Transcription of a particular gene.
 Exons (Coding sequence)
Exons are the functional portions of gene
sequences that code for protein.
 Introns (Non – coding sequence) or Intervening
sequences
Introns are the non-coding sequence which
separates the Exons.
 5’ End
The 5’ end contains (i) Open reading frame and
(ii) TATA Boxes

9. (i) Open reading frame
 A sequence with variable length.
 It does not contains stop codons and can be
translated.
 The sequence begin with ATG which exist at the
5’ end of the gene.
(ii) Tata Boxes
 TATA Boxes contains 20 – 30 bases.
 It directs important enzymes to the correct
initiation site of Transcription.
 Termination codon
 Termination codon is the 3’ end of the gene.
 It could be TAA, TAG or TGA

10. (i) Open reading frame
 A sequence with variable length.
 It does not contains stop codons and can be
translated.
 The sequence begin with ATG which exist at the
5’ end of the gene.
(ii) Tata Boxes
 TATA Boxes contains 20 – 30 bases.
 It directs important enzymes to the correct
initiation site of Transcription.
 Termination codon
 Termination codon is the 3’ end of the gene.
 It could be TAA, TAG or TGA