NEET Biology Line-by-Line NCERT Guide

Covering 50% of the entire NEET exam • Botany & Zoology High-Yield Framework.

1. Genetics & Molecular Basis of Inheritance

Incomplete Dominance: *Mirabilis jalapa* (4 o'clock plant) and *Antirrhinum majus* (snapdragon): Phenotypic and genotypic ratio are both $1:2:1$ (Red : Pink : White).
Codominance: ABO blood groups in humans ($I^A, I^B, i$). $I^A$ and $I^B$ completely express together as AB blood type.
Pleiotropy: Single gene affecting multiple phenotypic traits (e.g. Phenylketonuria - lack of enzyme phenylalanine hydroxylase causes mental retardation, reduced hair and skin pigmentation).
Polygenic Inheritance: Human skin color governed by 3 genes (A, B, C) producing bell-shaped continuous variation.

DNA Packaging: Nucleosome contains $200\text{ bp}$ of DNA wrapped around an octamer of basic histone proteins ($2 \times \text{H2A, H2B, H3, H4}$). $\text{H1}$ histone seals the DNA.
Meselson and Stahl Experiment (1958): Proved semiconservative replication using $^{15}\text{NH}_4\text{Cl}$ heavy nitrogen and $\text{CsCl}$ density gradient centrifugation in *E. coli*.
Lac Operon (Jacob & Monod): Negative and inducible regulation. Lactose / allolactose acts as inducer by binding repressor protein (encoded by $i$ gene), freeing the operator for RNA polymerase to transcribe $z$ ($\beta$-galactosidase), $y$ (permease), and $a$ (transacetylase).

ECG Waves: P-wave = Atrial depolarisation; QRS complex = Ventricular depolarisation (counting QRS gives pulse rate); T-wave = Ventricular repolarisation.
RAAS Mechanism: Low GFR $\to$ JG cells secrete Renin $\to$ converts Angiotensinogen to Angiotensin I $\to$ Angiotensin II (vasoconstrictor) $\to$ Adrenal cortex secretes Aldosterone $\to$ $\text{Na}^+$ and $\text{H}_2\text{O}$ reabsorption restored.
Counter-Current Mechanism: Henle's loop and vasa recta maintain medullary interstitial osmolarity gradient from $300\text{ mOsmol/L}$ in cortex to $1200\text{ mOsmol/L}$ in inner medulla.