This document provides an introduction to molecular genetics. It discusses several key topics: - Genetics is the study of heredity and how genetic information is transmitted from one generation to the next. It examines gene structure, function, and regulation at the molecular level. - There are two broad approaches in molecular genetics - forward genetics identifies genes involved in biological processes, while reverse genetics studies the effects of altering known genes. - Drosophila melanogaster was an important early experimental model due to traits like small size and visible mutations. Experiments with fruit flies helped establish chromosomes as the structures that pass traits between generations. - DNA was established as the genetic material through experiments showing that traits could be transformed between bacteria via

1. Introduction to Molecular
Genetics
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2. Genetics
• The study of heredity
• The study of how differences between
individuals are transmitted from one
generation to the next
• The study of how information in the
genes is used in the development and
functioning of the adult organism
2

3. Genetics Biochemistry
Gene products are studied
invivo through the genes that
encode them
Gene products are purified
and studied invitro
Genetic analysis tells you
that the product has a role in
the process
It doesn’t tell you how direct
the role is
Biochemistry tells you what a
protein can do invitro
It doesn’t tell you whether it
really does it invivo
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4. Three Major Areas of Genetics
Classical
Genetics
(Transmission)
Molecular
Genetics
Evolutionary
Genetics
Mendel’s Principles Genome Quantitative Genetics
Meiosis + mitosis DNA structure Population Genetics
Sex determination Chemistry of DNA Evolution
Sex linkage Transcription Speciation
Chromosomal mapping Translation
Cytogenetics Control of gene
expression
DNA cloning
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5. Molecular Genetics ?
Understanding the molecular basis of biological
processes through studies on the gene
Study of gene structure, function and regulation – below
the organism level
Study of genes and how they are expressed
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6. Chromosomal Regions
Heterochromatin
compact;
few genes;
largely structural role
Euchromatin
contains most of the
genes.
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7. Chromosome
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8. 8

9. 9

10. Two broad approaches
Forward/
Classical:
Reverse
:
biological
process
gene
in hand
identify
mutants
create
mutants
phenotype? biological
process
find
the gene
biochemical
function
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11. Classical Method
• Genotype Phenotype
– Discover new phenotype
– Prove that it has genetic basis (i.e. that you
discovered a new mutation)
– Find the gene that has mutated
– Understand what and how the wild type gene does
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12. Reverse genetics
• Genotype Phenotype
– Change something in a known gene
– Observe phenotypic effect
– Find out why you see what you see
– Understand what and how the wild type gene does
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14. 14

15. Molecular Genetics - Origins
• Thomas Hunt Morgan- Columbia University
• The physical nature of the gene
• A discovery in 1910 changed the course of genetics
• Developed experimental model for the study of
modern genetics- the fruit fly – Drosophila
melanogaster
• The white eyed male mutant appeared in a culture of
flies in the fly room and this was the beginning of a
search for mutants
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16. White and Wild type
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17. • Easy to cultivate
• Prolific progeny
• Small and inexpensive
• Large polytene
chromosomes
• Diploid number 8
• Many mutations
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18. 18

19. Hermann Joseph Muller
• X rays cause
mutations
• Produced a variety of
flies with phenotypes
such avestigial
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20. Alfred Sturdevant produced the first genetic
map from linkage experiments
• Genes were related to
position on the
chromosome map
• Mutants were related
to differences in the
appearance of the
polytene chromosomes
due to staining
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21. 21

22. DNA as Genetic Material Transformation
• Griffith in 1928 observed the change of
non-virulent organisms into virulent ones
as a result of “transformation”
– MacLeod and McCarty in 1944 showed that
the transforming principle was DNA
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23. 23

24. 24

25. Avery, McLeod, and McCarty
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26. Transforming principle
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27. Proof of the Transforming Principle
• Chemical analysis of sample containing the transforming
principle showed that the major component was a
deoxyribose -containing nucleic acid
• Physical measurements show that the sample contained a
highly viscous substance having the properties of DNA
• Incubation with trypsin or chymotrypsin, enzymes that
catalzye protein hydrolysis or with ribonuclease( RNase),
an enzyme that catalyzes RNA hydrolysis did not affect the
transforming principle
• Incubation with DNase, an enzyme that catalyzes DNA
hydrolysis inactivates the transforming principle
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28. Rosalind Franklin
• Technically and
scientifically a gifted
scientist
• Focused on the A form of
DNA and missed the
double helix
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29. The Race for the Double Helix
• Rosalind Franklin and Maurice
Wilkins at Kings College
• Rosalind’s famous x-ray
crystallography picture of the B form
held the secret, but she didn’t realize
its significance
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30. The Race for the Double Helix
• Watson and Crick formed
an unlikely partnership
• A 22 year old PhD and a
thirty + PhD “want to be”
embarked on a model
making venture at
Cambridge
• Used the research of
other scientists to
determine the nature of
the double helix
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31. Nucleic Acid Composition
DNA and RNA
• DNA – Basic Molecules
a. Purines – adenine and guanine
b. Pyrmidines – cytosine and thymine
c. Sugar – Deoxyribose
d. Phosphate phosphate group
http://www.dnai.org/index.htm - DNA background
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32. Prokaryote DNA
• Tightly coiled
• Coiling maintained by molecules similar to the
coiling in eukaryotes
• Circular ds molecule
• Borrelia burgdoferi ( Lyme Disease )has a linear
chromosome
• Other bacteria have multiple chromosomes
• Agrobacterium tumefaciens ( Produces Crown
Gall disease in plants) has both circular and linear
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33. Mitochondria
• Mitochondrial DNA( mt
DNA)
• 16,500 base pairs
• 37 genes
• 24 encode RNA
• Defects lead to diseases
that are related to
energy
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34. Chloroplast DNA
• Chloroplast DNA( cp DNA) is larger than
mitochondrial DNA
• 195,000 bp
• Genes for photosynthesis
• Cp ribosomal RNAs
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35. Heavy and Light N
Meselson and Stahl experiment
35

36. • In the first generation
of E. coli, all the DNA
was heavy
• After one generation,
the DNA was half
heavy and half light
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37. DNA Replication –Semi Conservative
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38. DNA Replication
• DNA opens at an Ori ( origin of replication)
• Combination of many enzymes coordinate the
replicative process
• Template strand used to make the copy
• DNA polymerases read the template and
match the complementary base
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39. Degradation of DNA
• Endonucleases cleave DNA and RNA, by
cutting between individual bonds
• Some endonucleases cleave one strand some
cleave both strands at a specific point or
sequence( restriction nucleasess)
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40. The Flow of Genetic Information
• from one generation to the next
– DNA stores genetic information
– Information is duplicated by replication and is
passed on to next generation
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41. The Flow of Genetic Information within a
single cell
• Process called gene expression
• DNA divided into genes
– transcription yields a ribonucleic acid (RNA) copy of
specific genes
– translation uses information in messenger RNA (mRNA)
to synthesize a polypeptide
• Also involves activities of transfer RNA (tRNA) and ribosomal
RNA (rRNA)
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42. RNA
Types of RNA
a. Messenger
b. Transfer
c. Ribosomal
d. micro RNAs ( regulatory RNAs)
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43. Chromosomes vs Genes
• A chromosome
constitutes an entire DNA
molecule + protein
– Protein = histones
– Supercoiled DNA in
nucleosomes
– Humans contain 46 such
molecules (23 pairs)
• 44 somatic chromosomes
• 2 sex chromosomes (X +Y)
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44. Chromosomes vs Genes
• Genes constitute
distinct regions on the
chromosome
• Each gene codes for a
protein product
• DNA -> RNA-> protein
• Differences in proteins
brings about differences
between individuals and
species
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45. How do chromosomes become double stranded?
Answer: DNA replication
• During the life of the
cell, each
chromosome of DNA
makes a copy of itself
• This must occur prior
to cell division to
insure each daughter
cell gets a complete
set
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46. Therefore, prior to dividing, any cell
must first replicate DNA
• Each single-stranded (SS)
chromosome duplicates
to become a double-
stranded (DS)
chromosome
• Example:
– A human cell is formed
with 46 SS chromosomes
– Each chromosome
replicates to produce 46
DS chromosomes
46

47. DNA replication
47

48. DNA replication occurs during the
life of a cell = the Cell Cycle
• DNA replicates (makes a copy of itself) to
produce DS chromosomes
• During this time, the cytoplasmic contents
also duplicate
• Spindle tubules form to aid in the process of
cell division
– Mitosis in body cells
– Meiosis in sex cells
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49. The cell cycle
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50. 50
Week Topic Objectives
1-2 How traits are transmitted:
Mendelian Inheritance
Define the features of Mendels experiments
Explain the Law of Segregation
Explain the Law of Independent Assortment
Explain what a di-hybrid cross is and what it tells
us.
Understand Dominance and Recessive
3 The chromosome theory of
Inheritance
Understand the Unit of Inheritance
Explain how sex chromosomes help us understand
heredity processes
Explain the process of chromosome non-
disjunction
4 Gene Interaction Define incomplete penetrance and variable
expressivity
Define epistatis and pleiotropy
5 Genetic Linkage and Chromosome
Mapping
Define gene linkage and map distance
Explain how recombination frequency is
determined

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6 Molecular Mechanisms of Mutation and
DNA Repair
Define mutation and why they are heritable.
Explain the difference between induced and spontaneous
mutations.
Define DNA repair
7 DNA Recombination and Exchange Define the Holliday model for DNA recombination.
Explain what is meant by Gene Conversion
8 Chromosome Structure Explain the difference between DNA and the
chromosome.
Define Chromatin.
Define Epigenetics
9 Gene Regulation in Prokaryotes - List the various ways that gene expression can be regulated
- Describe what the lac operon does and why E. coli regulates its
expression
-Describe how lactose induces the expression of the lac operon
- Deduce the genes affected in the lac operon by their phenotypes
and genetic behavior
10-11 Gene Regulation in Eukaryotes - Describe cis- and trans- active elements involved in
eukaryotic regulation
- Define epigenetics and explain how epigenetic mechanisms
regulate transcription
Explain imprinting and chromatin remodelling
- Explain the role of alternative splicing in gene regulation, and
how it is regulated
- Describe the role of miRNA in gene regulation

52. Texts
• Molecular Biology 4th Edition, Robert F. Weav
er, McGraw Hill
• Genes. VIII. PrenticeHall. Benjamin Lewin 2004
• Russell iGenetics , Molecular Approach 3rd
Edition.
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