CDS Biology · Free notes
Genetics and Evolution: CDS Biology
Genetics and Evolution has 13 past-year questions in CDS General Knowledge, from 2017 (II) to 2026 (II): 3 EASY, 8 MODERATE and 2 HARD. Three of them came in 2026, and two of those copy NCERT's sentences almost word for word, so read the Class 10 and 12 chapters closely. Only one needs working: a Mendel ratio, which is quick once you write out 1 TT : 2 Tt : 1 tt. The rest are single facts about DNA and chromosomes, genetic engineering, acquired traits and analogous organs.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Heredity and DNA
9 PYQsWhat chromosomes and genes are made of, how Mendel's crosses give their ratios, how the sex of a child is decided, and the enzymes and products of genetic engineering.
Evolution
4 PYQsWhy a skill learnt in life is not inherited, what Lamarck, Darwin and Hardy-Weinberg said, how variation and natural selection drive evolution, and how to tell homologous from analogous organs.
Formula & revision sheet
1 formulas · 6 reference tables · 12 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
1 formulas · 6 reference tables · 12 gotchas across all subtopics — the exam-eve cheat-sheet
Formulas (1)
Reference tables (3)
Chromosomes, DNA and genes7 rows
| Term | Fact |
|---|---|
| Histones | Basic proteins in the nucleus, bound to DNAQ CDS 2019 (I): histones are proteins present in the nucleus in association with DNA. |
| Photo 51 | X-ray picture of DNA by Rosalind FranklinQ CDS 2024 (I), HARD: Photo 51 is an image of DNA molecules. |
| Double helix | Watson and Crick, 1953 |
| Base pairs | A with T, G with C |
| Insulin gene | One functional gene in adult humansQ CDS 2017 (II), HARD: adult humans have one functional insulin gene. |
| Mutation | A change in the genetic materialQ CDS 2022 (I): a mutation in a virus is a change in its genetic material. |
| Human chromosome number | 46, in 23 pairs |
How sex is decided2 rows
| Egg from mother | Sperm from father | Child |
|---|---|---|
| X | X | XX: girlQ CDS 2020 (II): a normal girl gets one X from the mother and one X from the father. |
| X | Y | XY: boy |
Genetic engineering6 rows
| Tool or product | What it is or does |
|---|---|
| Restriction endonuclease | Cuts DNA at a specific sequence; used to form recombinant DNAQ CDS 2026 (II): exonucleases remove end nucleotides AND restriction endonucleases are used to form recombinant DNA; both statements are correct. |
| Exonuclease | Removes nucleotides from the ends of DNA |
| DNA ligase | Joins pieces of DNA |
| Plasmid | Small ring of bacterial DNA used as a vector |
| Human insulin | Made by genetically engineered bacteria |
| Bt cotton | Carries an insect-killing gene from Bacillus thuringiensisQ CDS 2022 (I): the false statement is that genetic modification is used only in plants. |
Watch out for (7)
- Histones live in the nucleus→ Chromosomes, DNA and genes
- Photo 51 is DNA, not a virus→ Chromosomes, DNA and genes
- Pure tall means TT only→ Mendel's monohybrid cross
- 3 : 1 is what you see, 1 : 2 : 1 is what they carry→ Mendel's monohybrid cross
- The mother can only give X→ How sex is decided
- Genetic engineering is not only for plants→ Genetic engineering
- Scissors and glue→ Genetic engineering
Reference tables (3)
Inherited and acquired traits, and the theories5 rows
| Person or principle | Key idea |
|---|---|
| Lamarck | Inheritance of acquired characters (rejected) |
| Darwin | Branching descent and natural selection |
| Hugo de Vries | Evolution by mutation |
| Hardy-Weinberg | Allele frequencies stay stable unless disturbedQ CDS 2026 (II): the wrong statement says Hardy-Weinberg makes allele frequencies unstable. |
| Weismann | Cut the tails of mice for generations; the young still had tails |
Variation and natural selection5 rows
| Source or process | What happens |
|---|---|
| Mutation | A change in the DNA creates a new variant |
| Sexual reproduction | Genes of two parents mix in new combinations |
| Asexual reproduction | Very little variation |
| Natural selection | Variants best suited to the environment survive and reproduce moreQ CDS 2021 (II): the false statement is that all variations in a species have equal chances of survival. |
| Genetic drift | Chance change in gene frequency in a small population |
Homologous and analogous organs3 rows
| Kind | Origin and function | Examples |
|---|---|---|
| Homologous | Same origin, different function | Forelimbs of human, whale and bat; thorn of Bougainvillea and tendril of Cucurbita |
| Analogous | Different origin, same function | Wings of bird and bat; wings of butterfly and bird; potato and sweet potatoQ CDS 2020 (II): bird and bat wings are analogous because they have a different origin and a common function. |
| Vestigial | Reduced, no longer used | Human appendix, wisdom teeth |
Watch out for (5)
- Learnt skills are not in the DNA→ Inherited and acquired traits, and the theories
- Hardy-Weinberg means stable→ Inherited and acquired traits, and the theories
- Variations are not equal in survival→ Variation and natural selection
- Analogous: different origin, same job→ Homologous and analogous organs
- Homologous shows divergence, analogous convergence→ Homologous and analogous organs
PYQ weightage by concept
7 concepts · 13 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
7 concepts · 13 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Chromosomes, DNA and genes | 5 | 38% |
| Genetic engineering | 2 | 15% |
| Mendel's monohybrid cross | 1 | 8% |
| How sex is decided | 1 | 8% |
| Concept | PYQs | Share |
|---|---|---|
| Inherited and acquired traits, and the theories | 2 | 15% |
| Variation and natural selection | 1 | 8% |
| Homologous and analogous organs | 1 | 8% |
Test yourself on a real paper
Sit a past CDS paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.