Mendelian ratios
| Cross | Phenotypic ratio | Genotypic ratio |
|---|---|---|
| Monohybrid (Tt × Tt) | 3 : 1 | 1 : 2 : 1 |
| Dihybrid (TtRr × TtRr) | 9 : 3 : 3 : 1 | — |
| Test cross (Tt × tt) | 1 : 1 | 1 : 1 |
| Incomplete dominance | 1 : 2 : 1 | 1 : 2 : 1 |
Mitosis vs meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Daughter cells | 2 | 4 |
| Chromosome number | Same (2n) | Halved (n) |
| Where | Somatic cells | Gamete formation |
| Variation | No | Yes (crossing over) |
Metaphase = chromosomes align at the equator. Anaphase = sister chromatids separate.
DNA base pairing
- A pairs with T (2 hydrogen bonds).
- G pairs with C (3 hydrogen bonds).
- In RNA, thymine is replaced by uracil.
Remember: "3 G-C bonds are stronger" — GC-rich DNA has a higher melting temperature.