Genetics – Study Notes for NEET‑Veterinary
(Designed for IIT‑JEE/competitive exam depth)
1. Overview
| Topic | Key Question | Why it matters for NEET‑Vet |
|---|---|---|
| Mendelian genetics | How do dominant/recessive alleles segregate? | Most exam questions test Punnett‑square logic. |
| Non‑Mendelian patterns | What are incomplete dominance, codominance, polygenic traits? | Used for pathology/clinical genetics. |
| Chromosome theory | How do X‑linked traits differ? | Many animal diseases are sex‑linked. |
| Gene expression | How do DNA → RNA → Protein? | Helps explain mutations & disease mechanisms. |
| Quantitative genetics | How to quantify selection in breeding programs? | Core of animal breeding & selection theory. |
2. Mendelian Genetics
2.1 The Law of Segregation
- Alleles segregate in gametes → 1:1 ratio in offspring.
- Genotype → Phenotype:
- Dominant allele (A) masks recessive (a).
- Homozygous dominant (AA) & heterozygous (Aa) → same phenotype.
2.2 Monohybrid Crosses
| Parental genotypes | Gametes | F1 genotypes | Phenotypic ratio |
|---|---|---|---|
| AA × aa | A | a | AA |
| Aa × Aa | A or a | AA, Aa, aa | 3 : 1 (dominant : recessive) |
Derivation (Punnett)
- Count all gametes → 4 boxes → fill → phenotype count.
2.3 Dihybrid Crosses
- Two independent genes (A/a × B/b).
- Punnett square → 16 boxes → typical phenotypic ratio 9 : 3 : 3 : 1.
Derivation
[
\frac{(A!B) + (aB) + (Ab) + (ab)}{(A!B) + (A b) + (aB) + (ab)} = 9:3:3:1
]
2.4 Incomplete Dominance
- Heterozygote phenotype is intermediate.
- Example: Citrus flower color (red × white → pink).
- Genotypic ratio: 1 : 2 : 1 → Phenotype: 1 red : 2 pink : 1 white.
2.5 Codominance
- Both alleles expressed simultaneously.
- Example: AB blood group (A × B → AB).
- Phenotype: 1 : 1 : 1 for AA : AB : BB.
2.6 Multiple Alleles
- One gene has >2 alleles.
- Example: Human blood group (IA, IB, i).
- Phenotypic ratios derived from the specific allele combinations.
2.7 Sex‑Linked Inheritance
| Trait | Chromosome | Phenotype in males | Phenotype in females |
|---|---|---|---|
| X‑linked recessive | X | 1 : 1 (affected vs. normal) | 1 : 2 (carrier vs. affected) |
| X‑linked dominant | X | 1 : 1 (affected vs. normal) | 1 : 1 |