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7.2 Maternal Effect, Maternal Inheritance & Plastid Inheritance — Test 1
Q1. Cytoplasmic (extrachromosomal) male sterility was first discovered in maize by:✓ M. A. Overman and H. E. Warmke
Q2. A mitochondrial mutation causes CMS, restorable by a dominant nuclear Rf gene. A CMS (rfrf) line is crossed with a homozygous Rf/Rf restorer; the F1 is selfed. The percentage of male-sterile F2 is:✓ 25
Q3. The direction of shell coiling in the snail Limnaea peregra is a classic example of:✓ Maternal effect (extra-chromosomal influence of the mother's genotype)
Q4. In Limnaea, a dextral heterozygous (Dd) female is crossed with a sinistral (dd) male. The genotype ratio of heterozygous : homozygous offspring is:✓ 1:1
Q5. A dextral male (s⁺s⁺) is crossed with a sinistral female (ss). F1 are all sinistral, and F2 are all dextral. This demonstrates:✓ Maternal effect (the mother's genotype governs the next generation)
Q6. In Neurospora, a 'stp' (mutant) maternal parent × normal male gives all stp progeny, while the reciprocal cross gives all normal. This is explained by:✓ Maternal (cytoplasmic) inheritance
Q7. A female with a mutant phenotype × wild-type male gives all mutant progeny; the reciprocal (mutant male × wild-type female) gives all wild-type. The inheritance is:✓ Mitochondrial (cytoplasmic)
Q8. In beach hoppers, larvae from dark-eyed mothers are initially dark-eyed but some later become light-eyed (matching their own genotype). This is due to:✓ Maternal effect (early phenotype set by the mother, later by own genotype)
Q9. The leaf variegation in Mirabilis jalapa (four o'clock plant) is an example of:✓ Chloroplast (plastid) inheritance
Q10. Extranuclear genes follow rules different from nuclear genes mainly because:✓ Their inheritance is commonly uniparental (maternal)
Q11. The 'iojap' striping in maize is an example of:✓ Plastid inheritance influenced by a nuclear gene
Q12. In Chlamydomonas, streptomycin resistance shown by Ruth Sager is inherited:✓ Uniparentally through the mt⁺ (maternal) parent — chloroplast inheritance
Q13. Heteroplasmy refers to:✓ The presence of a mixture of different organelle (e.g. mtDNA) genotypes within a cell
Q14. Mitochondrial diseases such as Leber's hereditary optic neuropathy (LHON) are inherited:✓ Maternally (through the mother)
Q15. A maternal-effect gene in Drosophila that establishes the anterior body axis of the embryo is:✓ bicoid
Q16. The key difference between 'maternal effect' and 'maternal (organelle) inheritance' is that maternal effect:✓ Involves the mother's nuclear genotype acting through egg products
Q17. In some plants (e.g. Pelargonium), plastids can be transmitted by both parents. This is called:✓ Biparental plastid inheritance
Q18. Petite mutants of yeast that show no linkage to any nuclear gene and are transmitted cytoplasmically are called:✓ Neutral/suppressive (cytoplasmic) petites
Q19. A reliable diagnostic test that a trait is cytoplasmically (not nuclearly) inherited is that:✓ Reciprocal crosses give different results
Q20. Match each example with its mechanism and select the correct option.✓ A-ii, B-i, C-iv, D-iii