Genetics & Plant Breeding — DU B.Sc. (Hons.) Botany Previous Year Question Papers

2. Attempt four questions in all. 4. Support your answers with well labelled diagrams wherever necessary. 5. All parts of a question should be answered together. 1. (a) Define any five of the following : (1x5=5) (i) Missense mutation (iii) Pure line selection (v) Lethal alleles (1) The phenomenon in plant breeding where the hybrid offspring exhibits superior traits, such as increased size or yield, compared to both parents is known as (ii) In - genetic inheritance, neither allele is completely dominant or recessive, and both alleles contribute equally to the phenotype of the offspring. (ill) The phenomenon in which a point mutation leads to the premature termination of a polypeptide chain is known as mutation. (iv) The experiment by Thomas Hunt Morgan with Drosophila melanogaster led to the discovery that the X chromosome carries the gene for red eyes and white eyes, demonstrating the principle of (v) A chromosomal aberration in which a segment of a chromosome is turned around 180 degrees is called (vi) In speciation, speciation occurs typically due to ecological or behavioral factors without physical barriers. (c) Match the following with their contributors any five) : (1x5=5) (i) Chromosomal Theory a. William Bateson of Inheritance (ii) Plant Selection Method b. Watson and Crick in plant breeding (iii) Linkage c. Alfred Sturtevant (iv) Coining of the d. Nilsson-Ehle term 'Genetics' (V) DNA structure •e. Theodore Boveri & Walter Sutton (vi) Genetic Mapping f. Thomas Hunt 2. Differentiate between any five of the following : (i) Complete linkage and incomplete linkage (ii) Test cross and reciprocal cross (iii) Polyploidy and aneuploidy (iv) Point mutations and frame shift mutations (v) Pure line selection and Mass selection (vi) Maternal inheritance and maternal effect 3. Write short notes on any five of the following : (i) Dosage compensation (ii) Mitochondrial inheritance (iii) Interspecific hybridization (iv) Transposable elements (v) Chemical mutagens (vi) Down's syndrome 4. (a) In a fruit fly, the genes for body color (B=black, b=grey) and wing size (W=long, w=vestigial) are linked. A test cross was done between a heterozygous black body, long winged fly (BbWw) and a homozygous recessive gray body, vestigial winged fly (bbww). Of the 200 offsprings produced, 180 had parental phenotypes (black body, long wings or gray body, vestigial wings) and 20 had the recombinant phenotypes (black body, vestigial wings or gray body, long wings). What is the recombination frequency between these two genes? (6) (b) What is epistasis? Explain the types of epistasis with examples. (3+6=15) 5. (a) Explain the inheritance of kappa particles in (b) Explain chloroplast and mitochondrial inheritance with suitable examples. (4+4=8) 6. (a) In a population of 1,000 individuals, 360 individuals have blue eyes (recessive trait). What are the allele frequencies for blue eyes (b) and brown eyes (B)? (7)