Genetics and Plant Breeding
Textbook: Essentials of Genetics, 5E
Chapter 1: An Introduction to Genetics
Professor Takahiro Kusakabe
Chapter Concepts
Genetics is the science of heredity. The discipline has a rich history and involves investigations or
molecules, cells, organisms, and populations, using many different experimental approaches. Not only
does genetic information play a significant role during evolution, its expression influences the functioning
of individuals at all levels. Genetics thus unifies the study of biology and has had a profound impact on
human affairs.
1.1 Genetics Has a Rich and Interesting History
Prehistoric Times: Domesticated Animals and Cultivated Plants
The Greek Influence: Hippocrates and Aristotle
1600–1850: The Dawn of Modern Biology
Charles Darwin and Evolution
1.2 Nucleic Acids and Proteins Serve As the Molecular Basis of Genetics
The Trinity of Molecular Genetics
The Structure of Nucleic Acids
The Genetic Code and RNA Triplets
Proteins and Biological Function
1.3 Genetics Has Been Investigated Using Many Different Approaches
1.4 Genetics Has a Profound Impact on Society
Eugenics and Euphenics
Genetic Advances in Agriculture and Medicine
Chapter 2: Mitosis and Meiosis
Professor Takahiro Kusakabe
Chapter Concepts
In every living thing there exists a substance referred to as the genetic material. Except in certain viruses,
this material is composed of the nucleic acid, DNA. A molecule of DNA is organized into units called
genes, the products of which direct the metabolic activities of cells. DNA, with its array of genes, is
organized into structures called chromosomes, which serve as vehicles for transmitting genetic
information. The manner in which chromosomes are transmitted from one generation of cells to the next,
and from organisms to their descendants, must be exceedingly precise. In this chapter we consider exactly
how genetic continuity is maintained between cells and organisms.
2.1 Cell Structure Is Closely Tied to Genetic Function
2.2 Chromosomes Exist in Homologous Pairs in Diploid Organisms
2.3 Mitosis Partitions Chromosomes into Dividing Cells
Interphase and the Cell Cycle
Prophase
Prometaphase and Metaphase
Anaphase
Telophase
2.4 The Cell Cycle Is Genetically Regulated
2.5 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and
Spores
An Overview of Meiosis
The First Meiotic Division: Prophase I
Metaphase, Anaphase, and Telophase I
The Second Meiotic Division
2.6 The Development of Gametes Varies during Spermatogenesis and Oogenesis
2.7 Meiosis Is Critical to the Successful Sexual Reproduction of All Diploid Organisms
2.8 Electron Microscopy Has Revealed the Cytological Nature of Mitotic and Meiotic
Chromosomes ③Chapter 3: Mendelian Genetics
Associate Professor Yutaka Banno
Chapter Concepts
Although inheritance of biological traits has been recognized for thousands of years, the first significant
insights into the mechanisms involved occurred about 135 years ago. In 1866, Gregor Johann Mendel
published the results of a series of experiments that would lay the foundation for the formal discipline of
genetics. Mendel’s work went largely unnoticed until the turn of the century, but in the ensuing years the
concept of the gene as a distinct hereditary unit was established. The ways in which genes, as members of
chromosomes, are transmitted to offspring and control traits were clarified. Research has continued
unabated throughout the twentieth century—indeed, studies in genetics, most recently at the molecular
level, have remained continually at the forefront of biological research since the early 1900s.
3.1 Mendel Used a Model Experimental Approach to Study Patterns of Inheritance
3.2 The Monohybrid Cross Reveals How One Trait Is Transmitted from Generation to
Generation
Mendel’s First Three Postulates
Modern Genetic Terminology
Punnett Squares
The Test Cross: One Character
3.3 Mendel’s Dihybrid Cross Revealed His Fourth Postulate: Independent Assortment
Mendel’s Fourth Postulate: Independent Assortment
The Test Cross: Two Characters
3.4 The Trihybrid Cross Demonstrates That Mendel’s Principles Apply to Inheritance of
Multiple Traits
The Forked-Line Method
3.5 Mendel’s Work Was Rediscovered in the Early 20th Century
Unit Factors, Genes, and Homologous Chromosomes
3.6 Independent Assortment Leads to Extensive Genetic Variation
3.7 Laws of Probability Help to Explain Genetic Events
3.8 Chi-Square Analysis Evaluates the Influence of Chance on Genetic Data
Chi-Square Calculations and Their Interpretation
3.9 Pedigrees Reveal Patterns of Inheritance in Humans
④Chapter 5: Sex Determination and Sex Chromosomes
Associate Professor Yutaka Banno
Chapter Concepts
In the biological world, a wide range of reproductive modes and life cycles are recognized. Asexual
organisms exist where no evidence of sexual reproduction is evident, while other species alternate
between short periods of sexual reproduction and prolonged periods of asexual reproduction. In most
diploid eukaryotes, however, sexual reproduction is the only natural mechanism that results in new
members of a species. Orderly transmission of genetic units from parents to offspring, and thus any
phenotypic variability, relies on the processes of segregation and independent assortment that occur
during meiosis. Meiosis produces haploid gametes so that, following fertilization, the resulting offspring
maintain the diploid number of chromosomes characteristic of their species. Thus, meiosis ensures
genetic constancy within members of the same species.
5.1 Life Cycles Depend on Sexual Differentiation
Chlamydomonas
Maize (Zea mays)
Caenorhabditis elegans
5.2 X and Y Chromosomes Were First Linked to Sex Determination Early in the 20th Century
5.3 The Y Chromosome Determines Maleness in Humans
Klinefelter and Turner Syndromes
47,XXX Syndrome
47,XYY Condition
Sexual Differentiation in Humans
The Y Chromosome and Male Development
5.4 The Ratio of Males to Females in Humans Is Not 1.0
5.5 Dosage Compensation Prevents Excessive Expression of X-Linked Genes in Humans and
Other Mammals
Barr Bodies
The Lyon Hypothesis
The Mechanism of Inactivation
5.6 The Ratio of X Chromosomes to Sets of Autosomes Determines Sex in Drosophila
5.7 Temperature Variation Controls Sex Determination in Reptiles
⑤Chapter 4: Modification of Mendelian Ratios
Associate Professor Toshihiro Kumamaru
Chapter Concepts
In Chapter 3, we discussed the simplest principles of transmission genetics. In this chapter we will restrict
our initial discussion to the inheritance of traits that are under the control of only one set of genes. In
diploid organisms, which have homologous pairs of chromosomes, two copies of each gene influence
such traits. The copies need not be identical because alternative forms of genes (alleles) occur within
populations. How alleles influence phenotypes is our primary focus. We will then consider how a single
phenotype can be controlled by more than one set of genes, a situation sometimes described as gene
interaction, and explore numerous examples.
4.1 Alleles Alter Phenotypes in Different Ways
4.2 Geneticists Use a Variety of Symbols for Alleles
4.3 Neither Allele Is Dominant in Incomplete, or Partial, Dominance
4.4 In Codominance, the Influence of Both Alleles in a Heterozygote Is Clearly Evident
4.5 Multiple Alleles of a Gene May Exist in a Population
The ABO Blood Groups
The Bombay Phenotype
The white Locus in Drosophila
4.6 Lethal Alleles Represent Essential Genes
4.7 Combinations of Two Gene Pairs Involving Two Modes of Inheritance Modify the 9:3:3:1
Ratio
4.8 Phenotypes Are Often Affected by More Than One Gene
Epistasis
Novel Phenotypes
Other Modified Dihybrid Ratios
4.9 Complementation Analysis Can Determine if Two Mutations Causing a Similar Phenotype
Are Alleles
4.10 X-Linkage Describes Genes on the X Chromosome
X-Linkage in Drosophila
X-Linkage in Humans
4.11 In Sex-Limited and Sex-Influenced Inheritance, an Individual's Sex Influences the
Phenotype
4.12 Phenotypic Expression Is Not Always a Direct Reflection of the Genotype
Penetrance and Expressivity
Temperature Effects
Onset of Genetic Expression
Genetic Anticipation
Genomic Imprinting
4.13 Extranuclear Inheritance Modifies Mendelian Patterns
Organelle Heredity: DNA in Chloroplasts and Mitochondria
Chloroplasts: Variegation in Four O'Clock Plants
Mitochondrial Mutations: poky in Neurospora and petites in Saccharomyces
Mitochondrial Mutations: Human Genetic Disorders
Maternal Effect: Limnaea Coiling
Chapter 5: Linkage and Chromosome Mapping in Eukaryotes
Professor Atsushi Yoshimura
Chapter Concepts
In this chapter we will discuss linkage, crossing over, and chromosome mapping in more detail. We will
conclude by entertaining the rather intriguing question of why Mendel, who studied seven genes in an
organism with seven chromosomes, did not encounter linkage. Or did he?
5.1 Genes Linked on the Same Chromosome Segregate Together
The Linkage Ratio
5.2 Crossing Over Serves As the Basis of Determining the Distance Between Genes During
Mapping
Morgan and Crossing Over
Sturtevant and Mapping
Single Crossovers
5.3 Determining the Gene Sequence During Mapping Relies on the Analysis of Multiple
Crossovers
Multiple Crossovers
Three-Point Mapping in Drosophila
Determining the Gene Sequence
A Mapping Problem in Maize
5.4 As the Distance between Two Genes Increases, Mapping Estimates Become More Inaccurate
Interference and the Coefficient of Coincidence
5.5 Drosophila Genes Have Been Extensively Mapped
5.6 LOD Score Analysis and Somatic Cell Hybridization Were Historically Important in Creating
Human Chromosome Maps
5.7 Linkage and Mapping Studies Can be Performed in Haploid Organisms
Gene-to-Centromere Mapping
5.8 Other Aspects of Genetic Exchange
Cytological Evidence for Crossing Over
Sister Chromatid Exchanges
5.9 Did Mendel Encounter Linkage?
Chapter 6: Quantitative Genetics
Professor Atsushi Yoshimura
Chapter Concepts
We have thus far discussed numerous examples of gene interaction as modifications of Mendelian ratios.
In each case, the resultant phenotypic variation was classified into distinct traits. Pea plants are tall or
dwarf; squash shape is spherical, disc-shaped, or elongated; and fruit fly eye color is red or white. These
phenotypes exemplify discontinuous variation, in which discrete phenotypic categories exist. Many other
traits in a population demonstrate considerably more variation and are not as easily categorized into
distinct classes. Such phenotypes are thus said to demonstrate continuous variation.
6.1 Continuous Variation Characterizes the Inheritance of Quantitative Traits
The Multiple-Factor Hypothesis
Additive Alleles: The Basis of Continuous Variation
Calculating the Number of Genes
The Significance of Polygenic Inheritance
6.2 The Study of Polygenic Traits Relies on Statistical Analysis
The Mean
Variance
Standard Deviation
Standard Error of the Mean
Analysis of a Quantitative Character
6.3 Heritability Is a Measure of the Genetic Contribution to Phenotypic Variability
Broad-Sense Heritability
Narrow-Sense Heritability
Artificial Selection
Twin Studies in Humans
6.4 Quantitative Trait Loci Can Be Mapped
⑧Chapter 7: Chromosome Mutations: Variation in Number and Arrangement
Associate Professor Hideshi Yasui
Chapter Concepts
In previous chapters, we have emphasized how mutations and the resulting alleles affect an organism’s
phenotype, and how traits are passed from parents to offspring according to Mendelian principles. In this
chapter we look at phenotypic variation that results from more substantial changes than alterations of
individual genes—modifications at the level of the chromosome.
7.1 Specific Terminology Describes Variations in Chromosome Number
7.2 Variation in the Number of Chromosomes Results from Nondisjunction
7.3 Monosomy, the Loss of a Single Chromosome, May Have Severe Phenotypic Effects
Cri-du-Chat Syndrome
7.4 Trisomy Involves the Addition of a Chromosome to a Diploid Genome
Down Syndrome
Viability in Human Aneuploidy
7.5 Polyploidy, in Which More than Two Haploid Sets of Chromosomes Are Present, Is Prevalent
in Plants
Autopolyploidy
Allopolyploidy
7.6 Variation Occurs in the Structure and Arrangement of Chromosomes
7.7 A Deletion Is a Missing Region of a Chromosome
7.8 A Duplication Is a Repeated Segment of the Genetic Material
Gene Redundancy and Amplification: Ribosomal RNA Genes
The Bar Eye Mutation in Drosophila
The Role of Gene Duplication in Evolution
7.9 Inversions Rearrange the Linear Gene Sequence
Consequences of Inversions during Gamete Formation
7.10 Translocations Alter the Location of Chromosomal Segments in the Genome
Translocations in Humans: Familial Down Syndrome
7.11 Fragile Sites in Humans Are Susceptible to Chromosome Breakage
Fragile X Syndrome (Martin–Bell Syndrome)
Fragile Sites and Cancer