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3.3 Recombination Mechanism & Complementation β Test 1
Q1. The undue tendency of closely linked genes/alleles to remain associated in a population rather than randomise is termed:β Linkage disequilibrium
Q2. In Drosophila males, homologues pair and segregate but crossing over does not occur. Segregation of the two alleles of a gene therefore takes place at:β Anaphase I
Q3. In Drosophila males there is complete linkage. The reason is:β Lack of synapsis with crossing over (achiasmate meiosis)
Q4. In a heterozygote, if crossing over occurs between the gene locus and the centromere, segregation of the two alleles occurs during meiosis at:β Either anaphase I or anaphase II
Q5. A diploid organism heterozygous at two loci can produce how many types of gametes (independent assortment)?β 4
Q6. A mechanism that can move a gene from one linkage group to another is:β Translocation
Q7. A chromosome aberration that changes the order of genes in a genetic map but does NOT alter the linkage group is:β Inversion
Q8. The essential recombination-promoting sites recognised by the RecBCD pathway in E. coli are known as:β chi sites
Q9. The non-covalent pairing intermediate formed during homologous strand exchange is the:β Joint molecule
Q10. Which set of steps occurs in one or more models of homologous recombination?β Single-strand nicking, double-strand cleavage, resolution
Q11. Seymour Benzer mapped fine structure by studying recombination between:β Lysis mutants of bacteriophage T4 (rII region)
Q12. In Benzer's complementation test, two phages with different mutations co-infect E. coli and produce normal plaques. He concluded the mutations were:β At different loci (different genes/cistrons)
Q13. The concept of the 'recon' (the smallest unit of recombination) was proposed by Benzer from his study of:β Lysis mutants of bacteriophage T4
Q14. A cis-trans complementation test is carried out to identify:β Whether two mutations are allelic (in the same gene)
Q15. Two mutations at different sites within the same gene X, both altering its function, are called:β Alleles
Q16. Two temperature-sensitive mutants of E. coli are mated and none of the exconjugants show the wild-type phenotype. The mutations are:β Allelic (same gene)
Q17. A cross between two homozygous recessive plants (both white-flowered) produces non-mutant (red) progeny. This indicates the mutations are:β In different genes (they complement)
Q18. An ideal model system for identifying the stage (anaphase I vs II) at which alleles segregate is:β Neurospora crassa
Q19. The occurrence of a tetratype tetrad in ascomycete fungi is possible only if crossing over occurred during the:β Four-strand (post-replication) stage
Q20. Match each pioneer/term with its contribution and select the correct option.β A-ii, B-iii, C-i, D-iv