NEET / State Class 12 Board (e.g. ISC) Biology Syllabus

State Mendel's Law of Independent Assortment.

Alleles of different genes assort independently of one another during gamete formation (applies to genes on different chromosomes).

What are the phenotypic and genotypic ratios of a Mendelian dihybrid cross (F2)?

Phenotypic ratio 9:3:3:1; genotypic ratio 1:2:1:2:4:2:1:2:1.

What is incomplete dominance? Give an example.

The heterozygote shows an intermediate phenotype between the two homozygotes. Example: pink flowers in Snapdragon (Antirrhinum) from red x white cross.

What is codominance? Give an example.

Both alleles express themselves fully in the heterozygote. Example: the AB blood group in humans, where both I^A and I^B are expressed.

How is sex determined in humans, and which parent determines the sex of the child?

XX = female, XY = male. The father determines sex, since he can contribute either an X or a Y sperm (males are heterogametic).

What is pleiotropy? Give an example.

A single gene influencing multiple phenotypic traits. Example: phenylketonuria, or sickle-cell gene affecting multiple characters.

What causes Down's syndrome and Klinefelter's syndrome?

Down's syndrome: trisomy of chromosome 21 (47, 21+). Klinefelter's syndrome: an extra X chromosome (47, XXY) producing a sterile male with some feminine features.

What is the genetic basis of sickle-cell anaemia?

An autosomal recessive point mutation: substitution of glutamic acid by valine at the 6th position of the beta-globin chain (GAG to GUG), caused by alleles Hb^S.

State Chargaff's rule for DNA base composition.

In double-stranded DNA, the amount of adenine equals thymine (A=T) and guanine equals cytosine (G=C); thus purines = pyrimidines.

Who proposed the double-helix model of DNA and what is its key dimensional feature?

Watson and Crick (1953). It is a right-handed double helix; one full turn is 3.4 nm long with 10 base pairs per turn, so adjacent bases are spaced 0.34 nm apart.

What experiments established DNA as the genetic material?

Griffith's transformation experiment, Avery-MacLeod-McCarty's biochemical work, and the Hershey-Chase experiment (using radioactive bacteriophages) confirmed DNA as the genetic material.

What did the Meselson-Stahl experiment prove?

That DNA replication is semiconservative (each daughter DNA has one parental and one newly synthesized strand), shown using N-15/N-14 isotopes in E. coli.

What are the salient features of the genetic code?

It is triplet, degenerate (more than one codon per amino acid), unambiguous, non-overlapping, comma-less, nearly universal, and has start (AUG) and stop (UAA, UAG, UGA) codons.

In the lac operon, what role does the repressor and the inducer (lactose) play?

The repressor protein binds the operator and blocks transcription. When lactose (the inducer) is present, it binds the repressor, inactivating it, so transcription of the structural genes (z, y, a) proceeds.

What was the goal of the Human Genome Project (HGP)?

To sequence all the base pairs in the human genome (~3.1 billion bp) and identify all genes, to understand human genetics and disease.

What is DNA fingerprinting based on, and who developed the technique?

Based on polymorphism in repetitive DNA sequences called VNTRs (variable number of tandem repeats/satellite DNA); developed by Alec Jeffreys.

State the theory of biogenesis and who disproved spontaneous generation.

Biogenesis states life arises only from pre-existing life. Louis Pasteur disproved spontaneous generation with his swan-necked flask experiments.

What did the Miller-Urey experiment demonstrate?

That simple organic molecules (amino acids) could form abiotically from a mixture of gases (CH4, NH3, H2, water vapour) sparked by electric discharge, supporting chemical evolution.

Define analogous and homologous organs with an example each.

Homologous organs: same structure/origin, different functions (e.g., forelimbs of whale, bat, human) showing divergent evolution. Analogous organs: different structure, similar function (e.g., wings of butterfly and bird) showing convergent evolution.

State the Hardy-Weinberg principle and its allele frequency equations.

In a large, randomly mating population with no evolutionary influences, allele and genotype frequencies remain constant. p + q = 1 and p^2 + 2pq + q^2 = 1, where p and q are allele frequencies.

What is industrial melanism (peppered moth) an example of?

Natural selection in action: after industrialization, dark-coloured (melanic) moths were favoured over light ones on soot-darkened trees, demonstrating directional selection.

Define adaptive radiation with an example.

The evolution of different species from a common ancestor adapted to different habitats/niches. Example: Darwin's finches of the Galapagos Islands.

Name the four levels of immune defense terms: innate vs acquired immunity.

Innate immunity is non-specific and present from birth (physical, physiological, cellular, cytokine barriers). Acquired (adaptive) immunity is pathogen-specific and has memory, mediated by B-lymphocytes (humoral) and T-lymphocytes (cell-mediated).

What is the difference between active and passive immunity?

Active immunity: the body produces its own antibodies after exposure to antigen/vaccine (slow, long-lasting). Passive immunity: ready-made antibodies are given from outside (e.g., colostrum, anti-tetanus serum) (fast, short-lived).

Which cells does HIV primarily attack, and what disease results?

HIV attacks helper T-lymphocytes (T-helper/CD4 cells), reducing immunity and causing AIDS (Acquired Immuno Deficiency Syndrome).

Name the causative organisms of malaria, typhoid, and pneumonia.

Malaria: Plasmodium (e.g., P. vivax, P. falciparum). Typhoid: Salmonella typhi. Pneumonia: Streptococcus pneumoniae / Haemophilus influenzae.

What is the difference between a benign and a malignant tumour?

Benign tumours remain at their site and do not spread (non-cancerous). Malignant tumours are cancerous: cells proliferate uncontrollably, invade surrounding tissue, and spread to distant sites (metastasis).

Which microbes are used to produce curd, and in the production of cheese and the antibiotic penicillin?

Curd: Lactobacillus (lactic acid bacteria, LAB). Cheese ripening: e.g., Propionibacterium sharmanii (large holes) and Penicillium roqueforti (Roquefort). Penicillin: the fungus Penicillium notatum/chrysogenum.

What are biofertilizers? Name three types.

Organisms that enrich soil nutrients. Examples: Rhizobium (symbiotic N-fixer in legume roots), Azospirillum/Azotobacter (free-living N-fixers), and mycorrhiza (Glomus) plus cyanobacteria (Anabaena, Nostoc).

What are the two key enzymes/tools used in recombinant DNA technology and their roles?

Restriction endonucleases cut DNA at specific palindromic recognition sites (producing sticky ends); DNA ligase joins DNA fragments. Vectors (e.g., plasmids, like pBR322) carry the foreign DNA into the host.

What is the function of Bt cotton and the cry genes?

Bt cotton is genetically engineered with cry genes from Bacillus thuringiensis, producing Bt toxin (a protoxin activated in the insect's alkaline gut) that kills bollworm pests.

What is the productivity-based and trophic structure of an ecological pyramid; which pyramid is always upright?

Pyramids of number, biomass, and energy represent the trophic structure. The pyramid of energy is always upright because energy decreases at each successive trophic level (only ~10% transferred per level, the 10% law).