Chapter 1
The Science of Genetics
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Chapter Outline
Three Great Milestones in Genetics
DNA as the Genetic Material
Genetics and Evolution
Levels of Genetic Analysis
Genetics in the World: Applications of
Genetics to Human Endeavors
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Three Great Milestones in
Genetics
Gregor Mendel: Genes and the rules of
inheritance
James Watson and Francis Crick: the
structure of DNA
The Human Genome Project: sequencing
DNA and cataloguing genes
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Mendel: Genes and the
Rules of Inheritance (1866)
 Genes—hereditary factors
responsible for traits
 Alleles —different forms
(versions) of hereditary
factors (genes)
 Traits —A physical
characteristic brought about
by the expression of a gene
or many genes.
 Rules of Inheritance
– Alleles of the same gene
separate during gamete
formation
– Alleles of different genes
are inherited independently
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Gene:DNA sequence (fragment) that holds the information for a
trait
Trait: a notable feature or quality in an individual that makes
us unique
Allele:an alternative form (versions) of a gene (one of a pair) that
occupy a specific position on a specific chromosome. Variation
among non-coding DNA sequences.
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Locus (plural loci): specific location of a gene (DNA sequence )
on a chromosome
Chromosome: nucleoprotein structure observed during
cell division
Mitosis: One (single) cell division producing two identical
daughter cells
Meiosis: Two cell divisions resulting in 4 cells NOT genetically
identical
What is a Gene?
 Genes are made of nucleic acids
 Nucleic acids are made of building
blocks called nucleotides
 Nucleotides have three components
– Sugar molecule (ribose or
deoxyribose)
– Phosphate molecule
– Nitrogen-containing molecule
(adenine-A-, guanine-G-, cytosineC-, thymine-T-, uracil-U-)
 RNA is ribonucleic acid
 DNA is deoxyribonucleic (OH)
acid
!!!! Splicing reaction
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The Structure of a Nucleotide
Nucleotide
Nucleoside
Watson and Crick:
The Structure of DNA (1953)
(Rosalind Franklin)
 Nucleotides are linked
in a chain through
sugar-phosphate
interactions
 DNA molecules are
made of two chains of
nucleotides wound
around each other in a
helix
 Base pairs hold the
chains together
– A pairs with T
– G pairs with C
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The Human Genome Project:
Sequencing DNA and
Cataloguing Genes
 Genome—the collection of
DNA molecules that is
characteristic of an organism
 Genomics is the analysis of
DNA sequences that make up
a genome
 Genomics involves DNA
sequencing technology,
robotics, and computer science
 The Human Genome Project
determined the sequence of
nucleotides in the DNA of the
human genome
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DNA as the Genetic Material
Information flows from DNA to RNA to
protein (Central Dogma).
In all cellular organisms, the genetic
material is DNA.
The genetic material
– Must be able to replicate
– Must contain information
– Must be able to change
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The Central Dogma of
Molecular Biology
 The flow of information is DNA  RNA protein.
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DNA Replication (duplication)
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DNA Replication
 Based on the complementary ( anti-parallel) nature
of the two strands of duplex DNA molecules.
 When the two parental strands are separated, the
separated strands can serve as template for the
synthesis of new strands.
 New strands are assembled by incorporating
nucleotides according to base-pairing rules.
 At the end of replication, each template strand is
paired with a newly synthesized partner strand.
 DNA replication is catalyzed by enzymes.
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Gene Expression:
Using Genetic Information
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Gene Expression
During transcription, an RNA molecule is
synthesized from a DNA template.
This messenger RNA (mRNA) molecules
contains the information needed to synthesize
a polypeptide.
During translation, the triplet codons in the
RNA specify the incorporation of particular
amino acids into a polypeptide chain.
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Proteome/Genome
Proteome/Genome—the collection of
all the different proteins (genes) in an
organism.
Humans have between 20,000 and
25,000 genes in the genome and
hundreds of thousands to millions of
proteins in the proteome.
Proteomics/Genomics—the study of
all the proteins (genes) in cells.
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The Central Dogma of
Molecular Biology
 The flow of information is DNA  RNA protein.
 Some viruses can use RNA as a template for the synthesis
of DNA in reverse transcription ( Human?).
 Many genes do not encode polypeptides; their end-products
are RNA molecules (microRNA and piRNA)
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Telomeres
The end of each chromosome is called a telomere and is
distinguished by a set of repeated sequences.
New repeats are added by a telomerase,
a reverse transcriptase that synthesizes DNA from a
RNA template.
Telomeres are required for the complete replication of the
chromosome because they protect the ends from being
degraded.
Telomerase activity:
“is thought to have major effects on cell life”
Mutation:
Changing Genetic Information
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Genetics and Evolution
Variation in the DNA sequence
makes it possible for species to evolve
over time.
Organisms with similar DNA sequences
are descended from a common
ancestor.
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A phylogenetic tree
A phylogenetic
tree, or phylogeny,
represents the
historical
relationships among
organisms.
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Evolution depends on the occurrence,
transmission, and spread of mutant genes
in groups of organisms.
DNA sequence data provide a way of
studying the historical process of evolution.
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Levels of Genetic Analysis
Geneticists approach their
science from different points of
view—from that of a gene, a DNA
molecule, or a population of
organisms.
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Classical Genetics
Based on analysis of the outcomes of crosses
between different strains of organisms.
Can be coordinated with studies of the
structure and behaviour of chromosomes.
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Molecular Genetics
Studies the replication, expression,
and mutation of genes at the
molecular level.
Rooted in the study of DNA sequences
and the manipulation of DNA
molecules.
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Population Genetics
Individuals within a population may
carry different alleles of genes.
Population genetics is based on
analyzing allele frequencies in a
population and determining whether
these frequencies changes over time.
Population genetics includes evolution
and the inheritance
of
complex
traits.
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Genetics in the World:
Genetics is relevant in many venues outside the
research laboratory.
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Genetics in Agriculture:
Selective Breeding
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Genetics in Agriculture:
Genetically Modified Organisms
Genetically
Modified
Organisms (GMOs)
are have been
altered by the
introduction of
foreign resistance
genes.
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Genetics in Medicine
 Inborn Errors of Metabolism are metabolic
abnormalities caused to mutant alleles.
 Molecular genetics
– new ways to detect mutant alleles (BRCA1).
– new ways to treat diseases.
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Genetics in Society
Economic impact—biotechnology
industry, pharmaceutical industry.
Legal impact—paternity testing,
forensics, identification
Can you patent a gene sequence?
Can you patent
a natural product?
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