UPHESC Assistant Professor Genetics & Plant Breeding PYQs

Concept: Association and dissociation of the two ribosomal subunits is controlled by Mg²⁺ concentration.

1. High Mg²⁺ (≈10–20 mM) keeps 30S + 50S as 70S (and even forms 100S dimers).
2. Lowering Mg²⁺ (≈1 mM) dissociates 70S → 30S + 50S (80S → 40S + 60S).
3. Mn, Zn, Ca do not play this structural role.

Short trick: Magnesium = 'glue' of ribosome subunits.

Concept: The 'mur' CMS was produced by Hinata and Konno (1979) by repeated backcrossing that placed the B. campestris (B. rapa) nucleus into Diplotaxis muralis cytoplasm.

1. Other alien CMS sources in Brassica: Ogura (Raphanus sativus), tour (B. tournefortii), Moricandia arvensis, Erucastrum canariense.
2. Polima and nap CMS are native to B. napus.

Short trick: mur CMS = Diplotaxis muralis cytoplasm + campestris nucleus (Hinata & Konno).

Concept: Synthesis of DNA on an RNA template by reverse transcriptase (Temin and Baltimore, 1970) is reverse transcription – seen in retroviruses such as HIV.

1. Transcription: DNA → RNA.
2. Translation: mRNA → protein.
3. Central dogma: DNA → RNA → protein (the normal flow).

Short trick: RNA → DNA = Reverse (Temin–Baltimore).

Concept: Robert W. Holley (1965) sequenced yeast alanine-tRNA and proposed the two-dimensional clover-leaf model.

1. Holley, Khorana and Nirenberg shared the 1968 Nobel Prize (genetic code).
2. Nirenberg – poly-U → phenylalanine; Khorana – synthetic repeating polymers.
3. Benzer – fine structure of rII locus (cistron, muton, recon). The 3-D L-shape was given by Kim/Klug (1974).

Short trick: Holley's clover leaf (2-D); Kim's L-shape (3-D).

Concept: A multiline is a mixture of several pure-line (isogenic) lines of a self-pollinated crop – each plant is homozygous, but the population is heterogeneous (for resistance genes).

1. Single-cross hybrid: heterozygous but homogeneous.
2. Synthetic and composite varieties: heterozygous and heterogeneous (cross-pollinated crops).
3. Multiline concept: Jensen (1952), Borlaug (1953).

Short trick: Multiline = many homozygous lines mixed → homozygous + heterogeneous.

Concept: Mendel's 1865 lecture, published 1866 in the Proceedings of the Natural History Society of Brünn, was titled 'Versuche über Pflanzen-Hybriden' – Experiments in (on) Plant Hybridization.

1. It was rediscovered in 1900 by de Vries, Correns and von Tschermak.
2. The pea (Pisum sativum) was his material, not his title.

Short trick: Versuche über Pflanzen-Hybriden = Experiments on Plant Hybrids.

Concept: Prokaryotic RNA polymerase holoenzyme = core enzyme (α₂ββ′ω) + σ factor; σ recognises the promoter (−10 and −35 boxes) and initiates transcription.

1. After initiation σ leaves; the core elongates.
2. Rho (ρ) factor helps in termination.

Short trick: Sigma = Start (promoter recognition); Rho = stop.

Concept: In adventitive (nucellar) embryony, embryos arise directly from somatic nucellus/integument cells – giving polyembryony in Citrus, mango and jamun.

1. Nucellar seedlings are true-to-type, virus-free clones used as rootstocks.
2. Apospory: embryo sac from a somatic (nucellar) cell; recurrent apomixis: unreduced embryo sac from the megaspore mother cell.

Short trick: Citrus–Mango–Jamun polyembryony = nucellar (adventitive) embryos.

Concept: Vivek QPM 9 (VPKAS Almora, 2008) is India's first marker-assisted QPM hybrid; the opaque-2 (o2) gene was transferred into the parents of Vivek Hybrid 9.

1. o2 raises lysine and tryptophan in maize endosperm (Mertz et al., 1964).
2. Rht-1/Norin-10 – dwarfing genes of wheat; Dee-gee-woo-gen – dwarfing gene (sd1) of rice.

Short trick: QPM = opaque-2 maize.

Concept: Co 0238 (Karan-4) is the early-maturing, high-sucrose sugarcane variety bred at Sugarcane Breeding Institute (ICAR), Karnal regional centre, released 2009.

1. It covered most of the cane area of UP, Punjab, Haryana and Bihar – called a 'wonder variety'.
2. 'Co' prefix = Coimbatore (SBI) canes.

Short trick: Co + number = sugarcane (Coimbatore).

Concept: Genetic assortative mating = mating of individuals more closely related (genetically alike) than random pairs – i.e. inbreeding.

1. It increases homozygosity in every generation.
2. Phenotypic assortative mating is based on similar appearance; disassortative mating ≈ outcrossing.
3. Panmixis = random mating; polycross = open pollination among selected clones.

Short trick: Genetically alike × alike = inbreeding.

Concept: Vavilov placed sorghum in the Abyssinian (Ethiopian) centre of origin, where its greatest diversity occurs.

1. Ethiopia/north-east Africa is the specific primary centre; 'Africa' is a continent, not a Vavilovian centre.
2. Mexico (South Mexican–Central American centre) – maize, cotton (G. hirsutum).

Short trick: Ethiopian centre: sorghum, coffee, teff, castor.

Concept: Running separate backcross programmes for each character at the same time (with the same recurrent parent) and then intercrossing the improved lines is the most practical approach.

1. Simultaneous transfer needs very large populations to recover all donor genes together.
2. Stepwise transfer (one trait after another) takes too long.
3. Simultaneous-but-separate saves time and keeps population size manageable.

Short trick: Parallel backcrosses, then combine.

Concept: In the standard comparison of recurrent selection schemes (following Comstock, Robinson and Harvey, 1949), the relative efficiency depends on the degree of dominance.

1. Incomplete (partial) dominance: RRS and RS for GCA are comparable and both are better than RS for SCA.
2. Complete dominance: RS for GCA, RS for SCA and RRS are equally effective.
3. Overdominance: RRS and RS for SCA are comparable and both are better than RS for GCA.
4. Epistasis is not the basis of this comparison. (The English 'R.S.S.' stands for reciprocal recurrent selection – RRS in the Hindi version.)

Short trick: Partial → GCA side; Over → SCA side; Complete (the midpoint) → all three equal.

Concept: P. R. Jennings (IRRI, 1964), in 'Plant type as a rice breeding objective', proposed the short-statured, stiff-strawed, erect-leaved, high-tillering, nitrogen-responsive rice plant type – the basis of IR 8.

1. Donald (1968) coined 'ideotype' with a wheat model.
2. Matsushima's work was on yield physiology of rice (later 'improved plant type' was by Khush, IRRI).
3. Chandler was IRRI's first director.

Short trick: Dwarf rice plant type → Jennings (1964).

Concept: Iojap ('Iowa' + 'japonica' striping) is a nuclear recessive gene (ij) of maize described by M. T. Jenkins (1924); in ij ij plants plastids become defective and the defect is then inherited maternally.

1. It shows a nuclear gene inducing a cytoplasmic (plastid) mutation.
2. Mirabilis jalapa – Correns's plastid inheritance; Pelargonium – Baur's biparental plastid inheritance.

Short trick: Iojap = Iowa maize.

Concept: The nucleosome 'beads-on-a-string' (11 nm) coils into the solenoid chromatin fibre of about 30 nm = 300 Å.

1. 1 nm = 10 Å, so 30 nm = 300 Å.
2. Next levels: 300 nm loops → 700 nm → 1400 nm metaphase chromatid.

Short trick: 11 nm → 30 nm (300 Å) solenoid.

Concept: A tertiary trisomic has an extra translocated chromosome made of arms of two non-homologous chromosomes.

1. Primary: extra normal chromosome.
2. Secondary: extra isochromosome (two identical arms).
3. Telotrisomic: extra telocentric (one arm only).

Short trick: Tertiary = Translocation chromosome.

Concept: Pusa Jai Kisan (Bio-902) of Indian mustard was selected from somaclonal variants of variety Varuna regenerated through tissue culture (IARI, 1993) – India's first somaclonal variety in Brassica.

1. Somaclonal variation = genetic variation among plants regenerated from cell/tissue culture (Larkin & Scowcroft, 1981).
2. It is not a mutagen-induced, interspecific or transgenic variety.

Short trick: 'Bio-902' = tissue culture (somaclone of Varuna).

Concept: Fluorescence in situ hybridization uses a labelled DNA probe that binds its target on fixed chromosomes – directly showing the physical position of a gene/sequence (GISH uses whole genomic DNA as probe).

1. Phage display – protein–ligand interaction screening.
2. MALDI-TOF – mass spectrometry of proteins.
3. Colony hybridization – screening bacterial clones, not chromosomes.

Short trick: See the gene glow on the chromosome = FISH.