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1.3 Gene Interactions & Epistasis — Test 1
Q1. When one gene masks or modifies the expression of a non-allelic gene, the phenomenon is called:✓ Epistasis
Q2. A 9:7 F2 ratio (e.g. two white-flowered lines giving purple F1, then 9 purple : 7 white) indicates:✓ Complementary gene interaction
Q3. An F2 dihybrid ratio of 9:3:4 is observed when the genes show:✓ Recessive epistasis
Q4. When dominant epistasis operates between two loci, the classic 9:3:3:1 ratio changes to:✓ 12:3:1
Q5. A 9:6:1 F2 ratio is characteristic of:✓ Polymeric (additive) gene interaction
Q6. A 13:3 F2 ratio is produced by:✓ Dominant suppression (inhibitory genes)
Q7. A 15:1 F2 ratio indicates:✓ Duplicate dominant genes
Q8. A black Labrador (BBEE) is crossed with a yellow Labrador (bbee); F2 segregates 9 black : 3 brown : 4 yellow. This is:✓ Recessive epistasis (ee epistatic to B/b)
Q9. In summer squash, white fruit (W) is dominant to coloured, and disc shape is dominant to sphere. A white-sphere × white-sphere cross gives 3/4 white-sphere and 1/4 yellow-sphere. The parental genotypes are:✓ Wwdd × Wwdd
Q10. Two pure-breeding white-flowered lines are crossed; F1 are purple and F2 segregate 9 purple : 7 white. The best conclusion is that the two mutations are:✓ Non-allelic and complementary
Q11. A leaf-pigment pathway is controlled by two independent genes A and B; AaBb selfed gives green : white : yellow = 9 : 3 : 4. This indicates:✓ Recessive epistasis
Q12. In a 9:3:3:1 ratio that is replaced by a 9:7 ratio, the underlying interaction is:✓ Complementation (complementary gene action)
Q13. Fruit colour in pepper (Capsicum) where two loci together determine a single character is best described as:✓ Gene interaction in which two loci determine one characteristic
Q14. A disc-shaped fruit plant is crossed with a long-fruit plant; F1 are disc and F2 give 9 disc : 6 sphere : 1 long. The genotype of the spherical F2 plants is:✓ A_ bb and aa B_
Q15. When two genes are involved in the same pathway and absence of either gene's function abolishes the end product, the fraction of F2 (from a dihybrid cross) showing the product is:✓ 9/16
Q16. Two interacting genes (independently assorting) act in the same pathway; absence of either gene's function abolishes the product. What fraction of F2 shows the product?✓ 9/16
Q17. A cross in which the F1 generation resembles both parents (showing characters of each) is an example of:✓ Codominance
Q18. In a coat-colour pathway, the genotype that suppresses expression of colour regardless of other loci (giving albino) in rabbits is:✓ cc (albino, recessive at C locus)
Q19. A cross between two homozygous recessive individuals (each white) yields non-mutant (coloured) progeny. This indicates that the mutations are:✓ In different genes (complementation)
Q20. Match each F2 ratio with the type of gene interaction and select the correct option.✓ A-ii, B-iv, C-i, D-iii