CUET UG Biology Syllabus

State Mendel's Law of Independent Assortment.

When two pairs of contrasting traits are considered together, the segregation of one pair of alleles is independent of the other pair (true for genes on different chromosomes). Demonstrated by Mendel's dihybrid cross.

What are the phenotypic ratios of a monohybrid and a dihybrid cross in the F2 generation?

Monohybrid cross F2 = 3:1; dihybrid cross F2 = 9:3:3:1.

Define incomplete dominance with an example.

Incomplete dominance is when the heterozygote shows an intermediate phenotype between the two homozygotes (neither allele is fully dominant). Example: Snapdragon (Antirrhinum) flower color — red x white gives pink (Rr); F2 ratio is 1:2:1.

Explain co-dominance using the human ABO blood group system.

Co-dominance is when both alleles express their effects fully in the heterozygote. In blood group AB, alleles I^A and I^B are both expressed, producing both A and B antigens. The system also shows multiple alleles (I^A, I^B, i).

What is pleiotropy? Give an example.

Pleiotropy is when a single gene affects multiple phenotypic traits. Example: phenylketonuria (one mutant gene causes mental retardation plus reduced hair and skin pigmentation); sickle-cell anaemia is also pleiotropic.

How is sex determined in humans, and what genotypes correspond to males and females?

Humans have XY-type sex determination. Females are XX (homogametic), males are XY (heterogametic). The sperm carries either X or Y, so the father determines the sex of the child.

Why is haemophilia called a sex-linked recessive disorder, and who is more commonly affected?

The gene is recessive and located on the X chromosome. Males (XY) need only one recessive allele to be affected, so they are affected more often; females must be homozygous recessive to be affected.

Name one example each of an autosomal dominant, autosomal recessive, and chromosomal Mendelian disorder in humans.

Autosomal dominant: Huntington's chorea (or Myotonic dystrophy). Autosomal recessive: sickle-cell anaemia, cystic fibrosis, phenylketonuria. Chromosomal: Down's syndrome (trisomy 21), Klinefelter's, Turner's syndrome.

Describe the chromosomal basis of Down's syndrome, Klinefelter's syndrome, and Turner's syndrome.

Down's syndrome: trisomy of chromosome 21 (47, an extra autosome). Klinefelter's syndrome: 47, XXY (male with extra X). Turner's syndrome: 45, X0 (female missing one X).

Why did Morgan choose Drosophila melanogaster (fruit fly) for genetic studies? Give two reasons.

It can be grown easily on synthetic medium, has a short life cycle (~2 weeks), produces a large number of progeny, has clear sexual dimorphism, and shows many hereditary variations visible under a low-power microscope.

What is the chemical evidence (Griffith and Avery/MacLeod/McCarty) that DNA is the genetic material?

Griffith's transformation experiment showed a 'transforming principle' transferred heredity in Streptococcus pneumoniae; Avery, MacLeod and McCarty identified that principle as DNA (DNase destroyed transformation, but proteases and RNase did not).

State Chargaff's rule for DNA base composition.

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

What are the key features of the Watson-Crick double helix model of DNA?

Two antiparallel polynucleotide strands coiled in a right-handed helix; sugar-phosphate backbones outside, bases inside paired by hydrogen bonds (A=T two H-bonds, G≡C three H-bonds); ~10 base pairs per turn, pitch 3.4 nm, distance between adjacent bases 0.34 nm.

What did the Hershey-Chase experiment prove and how?

It proved DNA, not protein, is the genetic material of bacteriophages. They labeled DNA with radioactive ³²P and protein with ³⁵S; only ³²P (DNA) entered the bacterial cells and was passed to progeny phages, while ³⁵S (protein coat) stayed outside.

Why is DNA replication described as semiconservative, and who demonstrated it?

Each new DNA molecule retains one parental (old) strand and one newly synthesized strand. Meselson and Stahl demonstrated this in E. coli using ¹⁵N/¹⁴N density-gradient (CsCl) centrifugation.

Differentiate the leading and lagging strands during DNA replication.

DNA polymerase synthesizes only 5'→3'. The leading strand is synthesized continuously toward the replication fork; the lagging strand is synthesized discontinuously as short Okazaki fragments (later joined by DNA ligase) away from the fork.

What are the three salient features of the genetic code?

The genetic code is a triplet (codon of 3 nucleotides), degenerate (most amino acids coded by more than one codon), and (nearly) universal; it is also non-overlapping, commaless, and unambiguous. AUG is the start (initiator) codon.

Name the three stop (nonsense) codons and the start codon.

Stop codons: UAA, UAG, UGA (they code for no amino acid and terminate translation). Start/initiator codon: AUG (codes methionine and also initiates translation).

What is the central dogma of molecular biology?

Genetic information flows from DNA → RNA → protein: DNA is transcribed into mRNA, which is translated into protein. (Reverse flow RNA → DNA occurs in retroviruses via reverse transcriptase.)

Explain the lac operon and the role of the inducer lactose.

The lac operon (regulated by Jacob and Monod) consists of a promoter, operator, and structural genes z, y, a. Normally the repressor (i gene product) binds the operator and blocks transcription. Lactose acts as an inducer, binding the repressor and inactivating it, so RNA polymerase transcribes the genes (negative regulation, inducible operon).

What is the goal and significance of the Human Genome Project (HGP)?

To sequence all ~3.1 billion base pairs of the human genome and identify all its genes (~20,000-25,000). It enabled understanding of gene function, disease genetics, and is a basis for bioinformatics.

What are DNA fingerprinting and VNTRs used for?

DNA fingerprinting identifies individuals by analyzing variation in repetitive DNA, especially VNTRs (Variable Number of Tandem Repeats / minisatellites). It is used in forensic identification, paternity testing, and pedigree analysis. Developed by Alec Jeffreys.

State the theory of natural selection as proposed by Darwin.

Organisms produce more offspring than can survive; individuals vary; those with favorable heritable variations survive and reproduce more (survival of the fittest); over generations this gradually changes populations and gives rise to new species. Differential reproduction is the key.

What is the Hardy-Weinberg principle and its equation?

In a large, randomly mating population with no evolutionary influences, allele and genotype frequencies remain constant across generations (genetic equilibrium). Equation: p² + 2pq + q² = 1, where p + q = 1 (p and q are allele frequencies).

List the five factors that disturb Hardy-Weinberg equilibrium (cause evolution).

Gene migration (gene flow), genetic drift, mutation, genetic recombination, and natural selection.

Differentiate analogous and homologous organs with an example of each.

Homologous organs have the same basic structure/origin but different functions (e.g., forelimbs of humans, whales, bats — evidence of divergent evolution/common ancestry). Analogous organs have different structures but similar functions (e.g., wings of butterfly and bird — evidence of convergent evolution).

Where and when did the Miller-Urey experiment fit into the origin of life, and what did it show?

Stanley Miller (and Urey) simulated early-Earth reducing atmosphere (CH₄, NH₃, H₂, water vapour) with electric sparks and produced amino acids, supporting the chemical/abiogenic origin of life (Oparin-Haldane hypothesis).

Distinguish active and passive immunity.

Active immunity: the body produces its own antibodies on exposure to antigens (natural infection or vaccination); slow but long-lasting. Passive immunity: ready-made antibodies are given directly (e.g., mother's colostrum, anti-venom injection); fast but short-lived.

Name the causative organism and a key symptom for malaria, typhoid, and amoebiasis.

Malaria: Plasmodium (protozoan, spread by female Anopheles mosquito) — recurring chills and high fever. Typhoid: Salmonella typhi (bacterium) — sustained high fever, weakness. Amoebiasis: Entamoeba histolytica (protozoan) — constipation, abdominal pain, stools with mucus and blood.

Classify the two main types of cancerous (malignant) tumour behavior and name the cells of HIV's main target.

Tumours are benign (remain at original site) or malignant (proliferate, invade and metastasize). HIV primarily infects and destroys helper T-lymphocytes (CD4+ T cells), causing AIDS.

What roles do microbes play in producing curd, antibiotics, and biogas?

Curd: Lactobacillus (LAB) bacteria coagulate milk protein. Antibiotics: e.g., Penicillin from the fungus Penicillium notatum (by Fleming). Biogas (mainly methane): methanogen bacteria like Methanobacterium acting on cattle dung (gobar gas).

What are biofertilizers and biocontrol agents? Give an example of each.

Biofertilizers are organisms that enrich soil nutrients, e.g., Rhizobium (nitrogen fixation in legume roots), Azospirillum, mycorrhiza (Glomus). Biocontrol agents control pests/diseases biologically, e.g., Bacillus thuringiensis (Bt) against insect larvae, Trichoderma against plant pathogens, ladybird against aphids.

Define plant breeding and name the main steps in developing a new crop variety.

Plant breeding is the purposeful manipulation of plant species to create desired varieties. Steps: collection of variability (germplasm), evaluation and selection of parents, cross-hybridization of selected parents, selection and testing of superior recombinants, and testing/release/commercialization of the new cultivar.

What is single-cell protein (SCP) and biofortification?

SCP is protein obtained from microbes (e.g., Spirulina, Methylophilus) grown in mass as an alternative source of protein for food/feed. Biofortification is breeding crops with higher levels of vitamins, minerals, or proteins (e.g., iron-rich rice, vitamin-A-enriched carrots, protein-rich wheat 'Atlas 66').

What are the three core techniques (tools) of recombinant DNA technology?

(1) Restriction enzymes (molecular scissors) to cut DNA at specific sites; (2) cloning vectors (e.g., plasmids) to carry and replicate the foreign DNA; (3) DNA ligase to join DNA fragments. Also: a competent host cell to transform.

What is a restriction endonuclease, and what type of ends does it create?

A restriction endonuclease cuts DNA at specific palindromic recognition sequences. Cutting between the same bases on both strands at slightly staggered positions produces single-stranded overhangs called 'sticky ends' (cohesive ends), e.g., EcoRI.

List the three steps of one PCR (Polymerase Chain Reaction) cycle.

(1) Denaturation — DNA strands separate at high temperature (~94°C); (2) Annealing — primers bind to complementary sequences at lower temperature; (3) Extension — Taq DNA polymerase synthesizes new strands. The cycle is repeated to amplify DNA exponentially.

Why is Agrobacterium tumefaciens important in genetic engineering, and what is its Ti plasmid?

Agrobacterium tumefaciens naturally transfers DNA into plant cells. Its Ti (tumour-inducing) plasmid is modified (disarmed) and used as a vector to deliver desired genes into plant cells, making it a key tool in producing transgenic plants.

What features must a good cloning vector possess?

An origin of replication (ori) for autonomous multiplication, a selectable marker (e.g., antibiotic resistance gene) to identify transformants, unique recognition (restriction) sites for inserting foreign DNA, and (ideally) low molecular size with high copy number.

What is gel electrophoresis used for in genetic engineering, and which way do DNA fragments move?

It separates DNA (or RNA) fragments by size. Since DNA is negatively charged (due to phosphate groups), fragments move toward the positive (anode) electrode through an agarose gel; smaller fragments move farther. Bands are visualized with ethidium bromide under UV light.

What is Bt cotton and how does the Bt toxin work?

Bt cotton is a transgenic crop carrying cry genes from Bacillus thuringiensis. The bacterium produces inactive protoxin crystals (Cry proteins); when eaten by the insect, the alkaline gut pH solubilizes and activates the toxin, which binds the midgut epithelium, creating pores that swell and lyse cells, killing the pest (e.g., bollworm).

What is RNA interference (RNAi) and how was it used to make pest-resistant tobacco (Meloidogyne resistance)?

RNAi is a cellular defense where double-stranded RNA silences a specific mRNA by complementary binding. Tobacco was made resistant to the nematode Meloidogyne incognita by introducing nematode-specific genes that produce dsRNA, silencing the parasite's mRNA so it cannot survive in the transgenic host.

What are gene therapy and ELISA, and give one application of each.

Gene therapy is correcting a genetic defect by inserting a functional gene into a patient (first used for ADA deficiency / SCID). ELISA (Enzyme-Linked Immuno-Sorbent Assay) detects pathogens/antibodies by antigen-antibody interaction; used to diagnose diseases like HIV/AIDS.

Name two products made using genetically engineered organisms (transgenic/recombinant products) in medicine.

Human insulin (Humulin, made in E. coli — produced as separate A and B chains then joined), human growth hormone, clotting factor VIII, hepatitis B vaccine, and recombinant interferon (any two).

How is recombinant human insulin produced, and how does it differ from earlier insulin?

The genes for insulin's A and B polypeptide chains are inserted into E. coli plasmids; the bacteria produce the chains separately, which are then extracted and joined by disulfide bonds. Earlier insulin was extracted from pig/cattle pancreas and could cause allergy; recombinant insulin (Humulin) is identical to human insulin.

Define a population and name any three of its characteristic attributes.

A population is a group of individuals of the same species living in a defined geographical area, sharing resources and able to interbreed. Attributes: birth rate (natality), death rate (mortality), sex ratio, age distribution (age pyramid), and population density.

Write the exponential and logistic population growth equations and define carrying capacity (K).

Exponential growth: dN/dt = rN (J-shaped curve, unlimited resources). Logistic growth: dN/dt = rN[(K − N)/K] (S-shaped/sigmoid curve, limited resources). Carrying capacity (K) is the maximum population size the environment can sustainably support.

Match these population interactions to their effects (+/−): mutualism, competition, predation, parasitism, commensalism, amensalism.

Mutualism (+ +): both benefit. Competition (− −): both harmed. Predation (+ −): predator benefits, prey harmed. Parasitism (+ −): parasite benefits, host harmed. Commensalism (+ 0): one benefits, other unaffected. Amensalism (− 0): one harmed, other unaffected.

What is an ecological pyramid, and which type is always upright?

An ecological pyramid is a graphical representation of the relationship between trophic levels in terms of number, biomass, or energy. The pyramid of energy is always upright (energy decreases at each successive trophic level due to the 10% law).

State the 10 percent law of energy flow in an ecosystem (Lindeman).

Only about 10% of the energy at one trophic level is transferred to and stored in the next trophic level; the remaining ~90% is lost mainly as heat (metabolic/respiration). This limits the number of trophic levels in a food chain.

Differentiate primary and secondary ecological succession.

Primary succession starts on a bare, lifeless area with no pre-existing soil (e.g., bare rock, new volcanic land, cooled lava) and is very slow; the first colonizers (pioneer species) are usually lichens. Secondary succession occurs where a community was removed but soil remains (e.g., abandoned farmland, burnt forest) and is faster.

Distinguish gross primary productivity (GPP) from net primary productivity (NPP).

GPP is the total rate of organic matter (energy) produced by photosynthesis. NPP is the GPP minus the energy used by producers in respiration (R): NPP = GPP − R. NPP is the biomass available to consumers (herbivores and decomposers).

What are the four levels (types) of biodiversity, and which level is measured by species richness?

Genetic diversity, species diversity, and ecological/ecosystem diversity (sometimes also molecular/community). Species diversity is measured by species richness (the number of species per unit area).

Explain in-situ and ex-situ conservation with one example each.

In-situ ('on site') conservation protects species in their natural habitat, e.g., national parks, wildlife sanctuaries, biosphere reserves, sacred groves. Ex-situ ('off site') conservation protects species outside their habitat, e.g., zoos, botanical gardens, seed banks, cryopreservation.

What is a biodiversity hotspot, and how many are recognized in India?

A biodiversity hotspot is a region with very high species richness and a high degree of endemism that is under serious threat of habitat loss. India has 4 hotspots: the Himalayas, the Western Ghats, the Indo-Burma region, and Sundaland (Nicobar Islands).

List 'The Evil Quartet' — the four major causes of biodiversity loss.

(1) Habitat loss and fragmentation (the most important cause), (2) over-exploitation, (3) invasion by alien (exotic) species, and (4) co-extinctions.

What do the IUCN Red List categories 'Endangered' and 'Extinct' indicate, and name one critically endangered/threatened Indian species.

The IUCN Red List documents the conservation status of species. 'Endangered' = at very high risk of extinction in the wild; 'Extinct' = no living individuals remain. Example threatened Indian species: the great Indian bustard, the one-horned rhinoceros, or the Asiatic lion.