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3.5 Complementation, the Cistron & Gene Conversion — Test 2
Q1. When two recessive mutations are placed in trans and the individual shows a MUTANT phenotype, the two mutations are:✓ Allelic (in the same gene/cistron)
Q2. Two true-breeding mutants with the same phenotype are crossed and the F1 is wild type. This shows the mutations are:✓ Non-allelic (they complement)
Q3. The cis-trans complementation test is used to determine whether two mutations:✓ Are allelic (in the same gene)
Q4. In E. coli, a complementation test between two mutations is most readily carried out by:✓ Obtaining merozygotes (partial diploids)
Q5. Seymour Benzer defined the 'recon' (the smallest unit of recombination) by studying:✓ rII mutants of bacteriophage T4
Q6. If a gene is mutated at two different sites giving two altered versions of that gene, the two versions are best called:✓ Alleles
Q7. Morgan found that linkage between genes is not absolute but is frequently broken during prophase by:✓ Recombination (crossing over)
Q8. In Neurospora, an ascus showing a 6:2 ratio (instead of the expected 4:4) indicates:✓ Gene conversion
Q9. The Holliday junction is a structure observed during:✓ Homologous recombination
Q10. A cell line that is RecA⁻/⁻ (lacking RecA protein) would most likely show:✓ A low level of recombination
Q11. Site-specific recombination (as opposed to homologous recombination) is carried out by enzymes that act as a:✓ Nuclease and ligase (a recombinase)
Q12. Recessive lethal alleles are never completely eliminated from a population because they are:✓ Maintained in heterozygotes (carriers)
Q13. Two mutant Drosophila lines (e.g. apricot and sepia eye colour) are crossed and the F1 are all wild type. The two mutations are:✓ Non-allelic (they complement)
Q14. The functional unit defined by the complementation test is the:✓ Cistron
Q15. Gene conversion differs from ordinary crossing over in that gene conversion is:✓ Non-reciprocal
Q16. Four independent mutants with a similar phenotype are tested pairwise. Mutant 1 complements 2, 3 and 4, but 2, 3 and 4 fail to complement each other. The number of complementation groups is:✓ 2
Q17. Site-specific recombination between two repeated sequences in INVERTED orientation flanking a segment results in:✓ Inversion of the segment
Q18. In the Cre/loxP system, two loxP sites in the SAME (direct) orientation lead Cre to:✓ Excise (delete) the intervening DNA as a circle
Q19. The maximum recombination frequency observable between two genes during meiosis is:✓ 50%
Q20. Match each term with its definition and select the correct option.✓ A-iii, B-i, C-ii, D-iv