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1.7 Gene Interactions & Epistasis — Test 2
Q1. A dihybrid F2 ratio of 9:7 represents which type of gene interaction?✓ Complementary gene interaction (duplicate recessive epistasis)
Q2. A modified F2 ratio of 15:1 indicates that the trait is controlled by:✓ Two genes (duplicate dominant epistasis)
Q3. The modified F2 ratio characteristic of dominant epistasis is:✓ 12:3:1
Q4. In Labrador retrievers, the cross BbEe × BbEe gives 9 black : 3 brown : 4 yellow. This is an example of:✓ Recessive epistasis (ee masks the B locus)
Q5. Two pure-breeding white-flowered lines are crossed; the F1 are purple and the F2 segregate 9 purple : 7 white. This indicates:✓ The two genes act complementarily (both needed for pigment)
Q6. In a biochemical pathway, two independent genes are each required for the end product; absence of either gives no product. After a dihybrid cross, the fraction of F2 showing the end product is:✓ 9/16
Q7. Two pure-breeding white-flowered plants are crossed and all F1 are red. The most likely explanation is:✓ Complementation between two genes
Q8. In chickens, comb shape gives a 9 walnut : 3 rose : 3 pea : 1 single F2 ratio. This indicates:✓ Two genes interacting (each affecting comb shape)
Q9. Two mutant plants — one taller than wild type, the other the same height — produce a double mutant that is even taller. This interaction is termed:✓ Synergistic interaction
Q10. The Bombay phenotype, in which an individual genetically ABO but homozygous recessive (hh) at the H locus appears blood group O, is an example of:✓ Recessive epistasis (hh masks the ABO genes)
Q11. A cross of disc-shaped × long-fruited plants gives disc F1 and an F2 of 9 disc : 6 spherical : 1 long. This ratio indicates:✓ Duplicate genes with cumulative (additive) interaction
Q12. Recessive epistasis gives which modified dihybrid F2 ratio?✓ 9:3:4
Q13. When a recessive mutation of either of two genes (A or B) in a pigment pathway gives white, the cross AaBb × aabb gives a phenotypic ratio of:✓ 3 white : 1 purple
Q14. A single gene that affects several different, seemingly unrelated traits shows:✓ Pleiotropy
Q15. Epistasis differs from dominance in that epistasis is an interaction between:✓ Two different genes (one masking another)
Q16. When a 1/16 proportion of progeny shows a particular (mutant) phenotype, the trait is most likely governed by:✓ Two independently assorting genes
Q17. A dominant allele at one locus that suppresses the expression of a dominant allele at another locus can give a modified ratio of:✓ 13:3
Q18. A cross between two genes in which both must be dominant to give a phenotype, otherwise white, illustrates which classic ratio in the F2?✓ 9:7
Q19. The various epistatic ratios (12:3:1, 9:3:4, 9:7, 15:1) are all modifications of the basic dihybrid ratio of:✓ 9:3:3:1
Q20. Match each interaction with its F2 ratio and select the correct option.✓ A-iii, B-i, C-ii, D-iv