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3.2 Gene Mapping & Three-Point Crosses — Test 1
Q1. The distance between bacterial genes determined from interrupted-mating (conjugation) experiments is measured in:✓ Minutes
Q2. Two linked genes 'a' and 'b' show 20% crossing over. The test-cross progeny of (++/++ × ab/ab) F1 are expected as:✓ ++/ab 40; ab/ab 40; a+/ab 10; +b/ab 10
Q3. Genes a and b are linked with 40% recombination. For the F1 ++/ab, the gamete proportions are:✓ ++30% : ab30% : +b20% : a+20%
Q4. R/r and S/s are linked genes 10 map units apart. In the cross Rs/rS × rs/rs, the percentage of Rs/rs progeny is:✓ 5
Q5. Two genes A and B are 10 cM apart in coupling (AB/ab). In a test cross (AB/ab × ab/ab), the ideal frequency of the ab/ab genotype is:✓ 45%
Q6. Two genes a and b are 10 cM apart and AaBb individuals (linked in trans) are sib-mated. The percentage of aabb progeny is approximately:✓ 6.25
Q7. Two genes A and B are 70 cM apart; heterozygotes are test-crossed. The number of parental-phenotype progeny will be:✓ Equal to recombinant progeny
Q8. Crossover percentages are J–M 20, J–L 35, J–N 70, L–K 15, M–N 50. The correct gene order is:✓ J, M, L, K, N
Q9. Given crossing-over percentages a–b 20%, b–c 28%, a–c 8%, the gene order is:✓ b, a, c
Q10. Recombination frequencies are X–Y = 12, X–Z = 4, Y–Z = 8. The order of loci is:✓ Y-X-Z
Q11. In a test cross of 1000 progeny: 450 red-long, 470 white-short, 42 red-short, 38 white-long. The recombination frequency is:✓ 0.08
Q12. If the average chiasma count is 50.6 per cell, the corresponding total map length is approximately:✓ 2530 cM
Q13. In a three-point test cross, X–Y = 32.5 mu, Y–Z = 20.5 mu, and the coefficient of coincidence is 0.886. The percentage of double recombinants is approximately:✓ ~6%
Q14. A LOD score of 3 corresponds to odds in favour of linkage of:✓ 1000 : 1
Q15. The genetic map and the physical map of the same genes are not identical because:✓ Recombination frequencies per kilobase are not uniform
Q16. Genes situated closer together on a chromosome have ___ chance of being separated than genes that are farther apart.✓ Lesser
Q17. With regard to a dihybrid cross, which statement is correct?✓ Tightly linked genes show very few recombinations
Q18. At the highest resolution of genetic mapping, recombination is found to be concentrated in:✓ Hotspots
Q19. The distribution of recombinants (crossovers) along a chromosome is generally:✓ Non-random and sex-specific
Q20. Match each quantity with its value/meaning and select the correct option.✓ A-ii, B-i, C-iv, D-iii