Download Chapter 1 The Science of Genetics

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.
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 acid
(OH)
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!!!! Splicing reaction
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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dX
dY
http://www.scripps.edu/romesberg/Research/BaseDesign.html
http://www.nature.com/nature/journal/v509/n7500/full/nature
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13314.html
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(miRNA) and piRNA]
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
Table 1. The match results of clean reads.
Yang Q, Hua J, Wang L, Xu B, et al. (2013) MicroRNA and piRNA Profiles in Normal Human Testis Detected by Next Generation
Sequencing. PLoS ONE 8(6): e66809. doi:10.1371/journal.pone.0066809
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066809
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.
Cytochrome B gene similarities
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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.
- Classical (Transmission) Genetics
- Molecular Genetics
- Population Genetics
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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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Model Genetics Organisms
---Drosophila melanogaster (fly)
---Escherichia coli ( bacteria)
---Caenorhabditis elegans (worm)
---Arabidopsis Thaliana (plant)
---Mus musculus (mice)
---Sacharomyces cerevisiae ( yeast)
--Homo sapiens (humans) –Clinical trails ….??
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