CSIR-NET LIFE SCIENCES

Unit 8: Inheritance Biology

Complete Topic-Wise Syllabus

Mendelian Genetics • Gene Interaction • Linkage • Mutation • Genetic Mapping • Human Genetics • Population Genetics • Chromosomal Alterations

A. Chromosomal and Extrachromosomal Inheritance

🧬 1. Principles of Mendelian Inheritance

Gregor Mendel and classical genetics
Gene, allele and locus
Law of segregation
Law of independent assortment
Dominant and recessive alleles
Monohybrid cross
Dihybrid cross
Test cross
Back cross
Probability in genetic analysis

🧬 Mendel's Two Major Laws:

Law of Segregation: The two alleles of a gene separate during gamete formation.

Law of Independent Assortment: Alleles of different genes assort independently when the genes are not linked.

🧪 2. Codominance

Both alleles are expressed in the heterozygous condition
Example: ABO blood group
I^A and I^B are codominant alleles

🔵 3. Incomplete Dominance

Heterozygote has an intermediate phenotype
Neither allele is completely dominant
Phenotypic ratio often differs from classical Mendelian ratio

📊 4. Penetrance and Expressivity

Penetrance = proportion of individuals with a genotype showing the phenotype
Complete penetrance
Incomplete penetrance
Expressivity = degree or intensity of phenotype
Variable expressivity

🔀 5. Gene Interactions

Allelic interactions
Non-allelic interactions
Epistasis
Hypostasis
Complementary gene action
Supplementary gene action
Duplicate gene interaction
Polymeric gene interaction

Gene Interaction	Basic Concept
Epistasis	One gene masks or modifies the effect of another gene.
Complementary interaction	Two genes are required together to produce a phenotype.
Duplicate genes	Either of two genes can produce the same phenotype.
Polymeric interaction	Multiple genes contribute to a common phenotype.

🧬 6. Pleiotropy

One gene affects multiple phenotypic traits
Single gene → multiple effects
Examples of pleiotropic genetic effects

🧬 7. Genomic Imprinting

Parent-of-origin-specific gene expression
Maternal imprinting
Paternal imprinting
DNA methylation
Histone modifications
Epigenetic inheritance

🔗 8. Linkage

Genes located on the same chromosome
Complete linkage
Incomplete linkage
Linked genes
Linkage groups

🔄 9. Crossing Over

Exchange of genetic material between homologous chromosomes
Occurs during prophase I of meiosis
Chiasmata
Recombination frequency
Genetic distance

📌 Mapping Formula:

Recombination Frequency (%) =
Number of recombinant offspring ÷ Total offspring × 100

1% recombination ≈ 1 map unit ≈ 1 centimorgan (cM)

♂️♀️ 10. Sex-Linked Inheritance

X-linked inheritance
Y-linked inheritance
X-linked dominant traits
X-linked recessive traits
Sex-linked disorders
Sex-limited traits
Sex-influenced traits

🧫 11. Mitochondrial Inheritance

Mitochondrial DNA
Maternal inheritance
Heteroplasmy
Homoplasmy
Mitochondrial genetic disorders

🌿 12. Chloroplast Inheritance

Chloroplast DNA
Non-Mendelian inheritance
Maternal inheritance
Biparental inheritance in some organisms
Plastid genetics

🌿 Extrachromosomal Inheritance:

Mitochondrial genes + Chloroplast genes → Cytoplasmic inheritance → Often shows maternal transmission → Does not follow simple Mendelian segregation

👩 13. Maternal Inheritance

Transmission through maternal cytoplasm
Maternal-effect genes
Cytoplasmic determinants
Distinction between maternal inheritance and maternal effect

B. Genes and Mutations

🧬 1. Alleles

Alternative forms of a gene
Wild-type allele
Mutant allele
Dominant allele
Recessive allele

🔢 2. Multiple Alleles

More than two alleles exist for a gene in a population
ABO blood group as a classical example
Dominance relationships among alleles

🧬 3. Pseudoalleles

Closely linked genes that behave like alleles
Functional relationship
Recombination between pseudoalleles

🧪 4. Complementation Test

Used to determine whether two mutations are in the same gene
Complementation
Non-complementation
Cis and trans relationships

🧪 Complementation Test:

If two recessive mutations complement each other → mutations are usually in different genes.

If they fail to complement → mutations are usually in the same gene.

⚠️ 5. Mutation

Heritable alteration in genetic material
Spontaneous mutations
Induced mutations
Point mutations
Insertion
Deletion
Substitution

🔤 6. Types of Point Mutations

Silent mutation
Missense mutation
Nonsense mutation
Synonymous mutation
Conservative substitution
Non-conservative substitution

🧬 7. Frameshift Mutations

Insertion of nucleotides
Deletion of nucleotides
Alteration of reading frame
Often produces major changes in protein sequence

☢️ 8. Causes of Mutation

DNA replication errors
Spontaneous chemical changes
UV radiation
Ionizing radiation
Base analogues
Alkylating agents
Intercalating agents
Oxidative damage

🔬 9. Mutation Detection

Phenotypic screening
Genetic screening
Molecular techniques
DNA sequencing
PCR-based detection
Restriction analysis

☠️ 10. Mutant Types

Lethal mutants
Conditional mutants
Temperature-sensitive mutants
Biochemical mutants
Auxotrophic mutants
Loss-of-function mutants
Gain-of-function mutants
Dominant-negative mutants

🧬 Important Mutant Classes:

Loss-of-function: Reduced or absent gene function.

Gain-of-function: New or increased gene activity.

Dominant-negative: Mutant protein interferes with the normal protein.

Conditional mutant: Phenotype appears only under specific environmental conditions.

🧬 11. Germinal vs Somatic Mutations

Feature	Germinal Mutation	Somatic Mutation
Location	Germ cells or their precursors	Somatic cells
Inheritance	Can be transmitted to offspring	Usually not transmitted to offspring
Effect	May affect entire organism/offspring	Usually restricted to cell lineage

C. Genetic Analysis

🗺️ 1. Linkage Maps

Genetic mapping
Gene order
Recombination frequency
Map units
Centimorgan
Two-point mapping
Three-point mapping

🧬 2. Molecular Markers

RFLP
RAPD
AFLP
SSR / microsatellites
SNP markers
DNA markers
Marker-assisted mapping

🌱 3. Molecular Mapping in Plants

Mapping populations
F₂ population
Backcross population
Recombinant inbred lines
Doubled haploid populations
QTL mapping

🐭 4. Mapping in Animals

Pedigree-based mapping
Linkage analysis
Molecular markers
QTL analysis
Genome-wide mapping

🦠 5. Mapping in Bacteria

Transformation
Conjugation
Transduction
Gene transfer frequencies
Interrupted mating
Recombination analysis

🧫 6. Tetrad Analysis

Ordered tetrads
Unordered tetrads
Parental ditype (PD)
Non-parental ditype (NPD)
Tetratype (T)
Gene-centromere mapping

🧬 Tetrad Classes:

PD → Parental ditype
NPD → Non-parental ditype
T → Tetratype

🦠 7. Transformation

Uptake of naked DNA by bacteria
Natural transformation
Artificial transformation
Competence
DNA integration

🔗 8. Conjugation

Direct transfer of DNA between bacterial cells
F plasmid
F⁺ cell
F⁻ cell
Hfr strains
F' plasmids
Interrupted mating

🦠 9. Transduction

Bacteriophage-mediated gene transfer
Generalized transduction
Specialized transduction
Phage DNA

🔬 10. Sex-Duction

Transfer of bacterial genes by F' plasmid
Partial diploid formation
Merodiploids

🧬 11. Fine Structure Analysis of Genes

Mutational mapping
Recombination within genes
Complementation
Functional units
Cistron
Recon
Muton

🌱 12. Development of Mapping Populations

F₂ populations
Backcross populations
Recombinant inbred lines
Doubled haploids
Near-isogenic lines
Mapping population size

D. Human Genetics

👨‍👩‍👧‍👦 1. Pedigree Analysis

Pedigree symbols
Family history
Autosomal dominant inheritance
Autosomal recessive inheritance
X-linked dominant inheritance
X-linked recessive inheritance
Y-linked inheritance
Mitochondrial inheritance

📌 Pedigree Analysis Strategy:

1. Determine whether affected individuals occur in every generation.
2. Check male-to-male transmission.
3. Compare affected males and females.
4. Look for maternal transmission.
5. Determine the most probable inheritance pattern.

📊 2. LOD Score

LOD = Logarithm of the Odds
Used for linkage analysis
Compares likelihood of linkage versus no linkage
Used in human genetic mapping

📈 LOD Score Concept:

LOD score = log₁₀ [Likelihood of linkage ÷ Likelihood of no linkage]

A high positive LOD score provides strong evidence for linkage.

🧬 3. Human Karyotype

Chromosome number
Autosomes
Sex chromosomes
Chromosome morphology
Banding techniques
Karyotyping

🧬 4. Numerical Chromosomal Disorders

Trisomy
Monosomy
Polyploidy
Nondisjunction
Chromosomal aneuploidy

🩺 5. Genetic Disorders

Single-gene disorders
Chromosomal disorders
Mitochondrial disorders
Multifactorial disorders
Inherited metabolic disorders

🧬 6. Examples of Genetic Disorders

Hemophilia
Color blindness
Sickle-cell anemia
Phenylketonuria
Thalassemia
Huntington disease
Cystic fibrosis
Down syndrome
Turner syndrome
Klinefelter syndrome

E. Quantitative Genetics

👥 1. Population Genetics

Genetic variation in populations
Allele frequency
Genotype frequency
Gene pool
Population structure

⚖️ 2. Hardy-Weinberg Equilibrium

Population genetic equilibrium
Allele frequencies
Genotype frequencies
Random mating
Large population
No mutation
No migration
No selection
No genetic drift

⚖️ Hardy-Weinberg Equation:

p + q = 1

p² + 2pq + q² = 1

Where:
p = frequency of one allele
q = frequency of the other allele
p² = homozygous genotype
2pq = heterozygous genotype
q² = second homozygous genotype

🧬 3. Factors Affecting Hardy-Weinberg Equilibrium

Mutation
Migration / gene flow
Natural selection
Genetic drift
Non-random mating

📊 4. Polygenic Inheritance

Multiple genes control a quantitative trait
Continuous variation
Additive gene action
Environmental influence
Phenotypic distribution

📈 5. Heritability

Proportion of phenotypic variation attributable to genetic variation
Broad-sense heritability
Narrow-sense heritability
Response to selection
Breeding value

📊 Heritability:

Broad-sense: H² = V_G / V_P

Narrow-sense: h² = V_A / V_P

Where:
V_G = Genetic variance
V_A = Additive genetic variance
V_P = Phenotypic variance

🧬 6. Molecular Mapping

Mapping genes using molecular markers
QTL mapping
Association mapping
Linkage mapping
SNP-based mapping
Genome-wide association studies

F. Structural and Numerical Alterations of Chromosomes

🔄 1. Chromosomal Recombination

Homologous recombination
Crossing over
Non-homologous recombination
Genetic exchange
Generation of genetic variation

✂️ 2. Deletion

Loss of a chromosome segment
Terminal deletion
Interstitial deletion
Gene dosage effects
Pseudodominance

➕ 3. Duplication

Repeated chromosome segment
Tandem duplication
Displaced duplication
Gene dosage effects
Evolution of gene families

🔄 4. Inversion

Chromosome segment reverses orientation
Paracentric inversion
Pericentric inversion
Effects on recombination
Inversion heterozygotes

🔀 5. Translocation

Movement of chromosome segment
Reciprocal translocation
Non-reciprocal translocation
Robertsonian translocation
Position effects
Gene dosage effects

Alteration	Major Change
Deletion	Loss of chromosome segment
Duplication	Additional copy of chromosome segment
Inversion	Chromosome segment reverses orientation
Translocation	Chromosome segment moves to another location

🧬 6. Ploidy

Haploid
Diploid
Triploid
Tetraploid
Polyploidy
Euploidy
Aneuploidy

➖ 7. Aneuploidy

Monosomy
Trisomy
Nullisomy
Tetrasomy
Nondisjunction

🌱 8. Polyploidy

Autopolyploidy
Allopolyploidy
Chromosome doubling
Polyploid evolution
Importance in plant breeding

🧬 9. Genetic Implications

Altered gene dosage
Reduced fertility
Abnormal meiosis
Gene disruption
Position effects
Phenotypic abnormalities
Evolutionary significance

🧬 Structural vs Numerical Changes:

Structural: Deletion, duplication, inversion and translocation.

Numerical: Aneuploidy and euploidy/polyploidy.