Chapter 1 The Science of Genetics © John Wiley & Sons, Inc

Chapter 1The Science of Genetics

© John Wiley & Sons, Inc.

Chapter Outline

Three Great Milestones in GeneticsDNA as the Genetic MaterialGenetics and EvolutionLevels of Genetic AnalysisGenetics in the World: Applications of

Genetics to Human Endeavors


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


Mendel: Genes and theRules 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


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-, cytosine-C-, thymine-T-, uracil-U-)

RNA is ribonucleic acid DNA is deoxyribonucleic acid


(OH)!!!! Splicing reaction

The Structure of a Nucleotide

Nucleoside

Nucleotide

Watson and Crick:The Structure of DNA (1953)

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


(Rosalind Franklin)


http://www.scripps.edu/romesberg/Research/BaseDesign.html http://www.nature.com/nature/journal/v509/n7500/full/nature13314.html

dX dY

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 © John Wiley & Sons, Inc.

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


The Central Dogma of Molecular Biology

The flow of information is DNA RNA protein.


DNA Replication (duplication)


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.


Gene Expression:Using Genetic Information


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.


Proteome/GenomeProteome/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.


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]© John Wiley & Sons, Inc.

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.0066809http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066809

TelomeresThe 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


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.


A phylogenetic tree

A phylogenetic tree, or phylogeny, represents the historical relationships

among organisms.

Cytochrome B gene similarities


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.


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

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.


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.


Population GeneticsIndividuals 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.


Genetics in the World:


Genetics is relevant in many venues outside the research laboratory.

Genetics in Agriculture:Selective Breeding


Genetics in Agriculture:Genetically Modified Organisms

Genetically Modified Organisms (GMOs) are have been altered by the introduction of foreign resistance genes.


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.


Genetics in SocietyEconomic impact—biotechnology industry,

pharmaceutical industry.

Legal impact—paternity testing, forensics, identification

Can you patent a gene sequence?

Can you patent a natural product?



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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Chapter 1 The Science of Genetics © John Wiley & Sons, Inc