⚡ Final Checking Before Exam
CSIR-NET • GATE • USMLE • NEET-PG • Degree Finals
🧬 Genetics: One Night Revision & Cram Sheet
Explain how hereditary differences are transmitted through individuals, chromosomes, organelles, and populations, and how to read that transmission in a pedigree or a quantitative trait when a designed cross is not available.
🌟 Core Axioms & High-Yield Golden Rules
8 Core PrinciplesNon-negotiable foundational truths frequently tested in direct conceptual and numerical exam questions. Click checkbox to mark as mastered.
Mendel's Law of Segregation: Two alleles for a gene separate during anaphase I of meiosis so each gamete carries only one allele.
💡 Monohybrid: 3:1 pheno, 1:2:1 genoMendel's Law of Independent Assortment applies only to genes located on different chromosomes or very far apart on the same chromosome.
💡 Dihybrid: 9:3:3:1 ratioEpistasis modifications: Recessive epistasis gives 9:3:4 (e.g. coat color in mice); Dominant epistasis gives 12:3:1; Duplicate recessive gives 9:7; Duplicate dominant gives 15:1.
💡 9:3:4 = Recessive | 12:3:1 = DominantGenetic map distance: 1 map unit (centiMorgan / cM) = 1% recombination frequency. Maximum observable recombination frequency between linked genes is 50%.
💡 1 cM = 1% RF; Max RF = 50%X-linked recessive inheritance: Trait is more common in males, passes from carrier mother to son (skips generations); affected father NEVER passes trait to son.
💡 No father-to-son X transmissionMitochondrial inheritance: Exclusively maternal transmission. An affected mother transmits trait to ALL her children; an affected father transmits to NONE.
💡 Maternal inheritance = All maternal offspringHardy-Weinberg equilibrium assumptions: Large population, random mating, no mutation, no migration (gene flow), no natural selection.
💡 p + q = 1 | p^2 + 2pq + q^2 = 1Aneuploidies to remember: Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), Trisomy 13 (Patau syndrome), 45,X (Turner syndrome), 47,XXY (Klinefelter syndrome).
💡 21 = Down | 18 = Edwards | 13 = Patau📚 Chapter-by-Chapter Rapid Cram Breakdown
12 ModulesHigh-density review of every curriculum chapter. Click any chapter title to view full in-depth lecture notes.
Ch 01
Mendelian inheritance →
- Master Blending versus particles: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master pea experiments: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master segregation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master independent assortment: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master test cross: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 1.
- Master Incomplete dominance: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master codominance: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master multiple alleles: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master lethal alleles: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master pleiotropy: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 2.
- Master XY, XO, ZW, haplodiploidy: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Morgan’s white eye: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master haemophilia and colour vision: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Y linkage: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master X-inactivation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 3.
Ch 04
The chromosomal basis →
- Master Sutton–Boveri: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master linkage: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master crossing over: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master centimorgans: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master double crossovers: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 4.
Ch 05
Cytogenetics →
- Master Karyotype and G-banding: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master polyploidy: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master aneuploidy: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master nondisjunction: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master deletions and duplications: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 5.
- Master F+, F−, Hfr: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master time-of-entry mapping: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master transformation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master generalised and specialised transduction: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master complementation and the cistron: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 6.
- Master Molecular classes: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master loss and gain of function: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master haploinsufficiency: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Ames test: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master trinucleotide repeats: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 7.
- Master Human mitochondrial DNA: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master heteroplasmy: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master *Mirabilis* variegation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master maternal effect in snail coiling: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 8.
Ch 09
Population genetics →
- Master Allele and genotype frequencies: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Hardy–Weinberg: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master carrier frequency: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master selection: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master mutation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 9.
Ch 10
Quantitative genetics →
- Master Continuous traits: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Nilsson-Ehle: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master variance components: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master narrow-sense heritability: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master response to selection: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 10.
- Master Symbols: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master autosomal, X-linked, and mitochondrial patterns: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master twin studies: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master a conditional risk calculation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 11.
- Master Consanguinity: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master founder effects: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master the boundary with human evolutionary history: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
⚡ Quick Trigger: Remember core regulatory checkpoint and structural distinction for Chapter 12.
⚖️ Must-Know Comparison & Distinction Tables
1 TablesSide-by-side matrices comparing commonly confused biological mechanisms, kinetic types, and pathways.
Modified Dihybrid F2 Phenotypic Ratios (Epistatic Interactions)
| Epistasis Type | F2 Phenotypic Ratio | Classical Example | Biochemical Mechanism |
|---|---|---|---|
| Recessive Epistasis | 9 : 3 : 4 | Coat color in Labrador retrievers / mice | Homozygous recessive 'ee' masks both B and b alleles |
| Dominant Epistasis | 12 : 3 : 1 | Fruit color in summer squash | Dominant 'W' inhibits enzyme converting white to color |
| Duplicate Recessive | 9 : 7 | Flower color in sweet pea (Bateson & Punnett) | Both dominant alleles (A_B_) needed for functional pathway |
| Duplicate Dominant | 15 : 1 | Seed capsule shape in shepherd's purse | Either dominant allele (A_ or B_) is sufficient for trait |
⚠️ Examiner Traps & Common Student Mistakes
1 PitfallsClassic trap questions designed by examiners to catch uncritical students. Don't lose easy marks here!
❌ Pitfall
Can Recombination Frequency Exceed 50%?
What Students Wrongly Think:
Calculating RF from distances and getting 65 cM, then expecting 65% recombinant gametes.
✅ Scientific Reality:
Even if physical distance is >50 cM, multiple crossovers occur, so the MAXIMUM observed percentage of recombinant gametes in a test cross can NEVER exceed 50%.
💡 Exam Pro-Tip: If map distance is 80 cM, observed recombination frequency is 50% (indistinguishable from independent assortment).
📐 Key Formulas & Numerical Constants
3 FormulasHardy-Weinberg Principle
p^2 + 2pq + q^2 = 1 and p + q = 1p = dominant allele freq; q = recessive allele freq; 2pq = carrier/heterozygote frequency.
Recombination Frequency
RF = (Total Recombinants / Total Progeny) * 100%Directly gives map distance in centiMorgans (cM).
Coefficient of Coincidence & Interference
CoC = Observed DCO / Expected DCO; Interference (I) = 1 - CoCMeasures whether a crossover in one region suppresses (I > 0) or enhances (I < 0) a crossover nearby.
🏛️ Landmark Scientists & Nobel Discoveries
6 PioneersFrequently tested in historical milestone and match-the-following exam questions.
Frederick Sanger
🏅 Two Nobel Prizes in Chemistry: 1958 (Unshared, for determining the complete primary amino acid structure of insulin) and 1980 (Shared, for inventing dideoxy DNA sequencing)Major landmark discoveries
Gregor Johann Mendel
🏅 Pre-dated the Nobel Prize; unanimously recognized as the Father of Modern GeneticsMajor landmark discoveries
Thomas Hunt Morgan
🏅 Nobel Prize in Physiology or Medicine (1933) for his discoveries concerning the role played by the chromosome in heredityMajor landmark discoveries
Barbara McClintock
🏅 Nobel Prize in Physiology or Medicine (1983) for her discovery of mobile genetic elementsMajor landmark discoveries
James Watson & Francis Crick
🏅 Nobel Prize in Physiology or Medicine (1962) for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living materialMajor landmark discoveries
Susumu Tonegawa
🏅 Nobel Prize in Physiology or Medicine (1987) for his discovery of the genetic principle for generation of antibody diversityMajor landmark discoveries
🎯 Rapid-Fire Active Recall Checklist
3 QuestionsTest your memory before stepping into the exam hall. Try to answer mentally, then tap "Reveal Answer" to verify!
Hardy-Weinberg
What is the carrier frequency (2pq) for an autosomal recessive condition affecting 1 in 10,000 live births?
Mendelian Genetics
What phenotypic ratio in a dihybrid testcross indicates independent assortment?
Chromosomal Abnormalities