Inheritance and Variation — Class 12 Maharashtra HSC Biology revision notes
A 10-page visual revision sheet for Inheritance and Variation, written for Class 12 Maharashtra HSC Biology. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDF
Inheritance and Variation in one look
factors that don't blend, chromosomes that carry them, and the ways both get bent
Chromosomes and the Mechanism of Inheritance
- heredity: transmission of genetic information from one generation to the next
- Gregor Mendel worked out inheritance by hybridizing garden pea (Pisum sativum)
- this was before chromosomes or genes were even known
- he studied seven contrasting traits, one or a few at a time
- treated results mathematically: counted ratios, not just descriptions
- he called the unit of heredity a factor
- factors occur in pairs, pass through gametes, segregate without ever blending
- these factors are what we now call genes
Why Mendel succeeded
- large sample sizes, carefully planned crosses
- tracked one to three traits at a time, never everything at once
- he chose the pea for its easily recognised contrasting characters, each controlled by a single factor
Mendel's Seven Traits in the Pea Plant
- Seed shape: round (dominant) vs wrinkled (recessive)
- Seed colour: yellow (dominant) vs green (recessive)
- Pod shape: inflated (dominant) vs constricted (recessive)
- Pod colour: green (dominant) vs yellow (recessive)
- Flower colour: purple (dominant) vs white (recessive)
- Flower location: axial (dominant) vs terminal (recessive)
- Plant height: tall (dominant) vs short/dwarf (recessive)
Page 1 of 10. The full sheet, all 10 pages, opens free in the app.
What this Inheritance and Variation sheet covers
- Chromosomes and the Mechanism of Inheritance
- Why Mendel succeeded
- Mendel's Seven Traits in the Pea Plant
- Seed shape
- Seed colour
- Pod shape
- Pod colour
- Flower colour
- Flower location
- Plant height
- Genetic Terminology
- Mendel's Laws of Inheritance
- Monohybrid cross: pure tall x pure dwarf
- Parents
- F1
- F2
- F1 x F1: the monohybrid Punnett square
- Dihybrid cross
- F2 Ratios at a Glance
- Monohybrid, genotypic
- Monohybrid, phenotypic
- Dihybrid, phenotypic
- Back Cross and Test Cross
- Back cross
- Test cross
- Deviations from Mendelism
- Deviations from Mendelism, Sorted
- Two interacting alleles
- Multiple alleles
- Polygenic inheritance
- Pleiotropy
- Incomplete Dominance vs Co-dominance
- Incomplete dominance
- Co-dominance
- Chromosomal Theory of Inheritance
- Structure of a chromosome
- Four shapes, by centromere position
- X Chromosome vs Y Chromosome
- X
- Y
- Linkage and Crossing Over
- Morgan's Drosophila crosses
- Autosomal Inheritance
- Sex Linked Inheritance
- Sex Linkage, Four Types
- X-linked
- Y-linked (holandric)
- Complete sex linkage
- Incomplete (XY-linked)
- Colour blindness and Haemophilia
- Sex Determination
- Four Sex Determination Systems, Compared
- XX-XY (mammals)
- ZW-ZZ (birds)
- Haplo-diploid (honey bees)
- Environmental (Bonellia)
- Genetic Disorders: Mendelian vs Chromosomal
- Mendelian disorders
- Chromosomal disorders
- Ploidy: euploidy vs aneuploidy
- Chromosomal Disorders, by Non-Disjunction
- Thalassemia
- Traps that cost marks
- Tricks that save time
How CapCompass uses this sheet
These notes are not a standalone PDF. CapCompass plans Biology chapter by chapter against your real exam dates and free hours, and when the plan reaches Inheritance and Variation the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.
More Biology Class 12 revision notes
- Biodiversity, Conservation and Environmental Issues
- Biotechnology
- Control and Co-ordination
- Ecosystems and Energy Flow
- Enhancement of Food Production
- Human Health and Diseases
- Molecular Basis of Inheritance
- Organisms and Populations
- Origin and Evolution of Life
- Plant Growth and Mineral Nutrition
- Plant Water Relation
- Reproduction in Lower and Higher Animals
- Reproduction in Lower and Higher Plants
- Respiration and Circulation