Unit 4: Linkage, Chromosome Mapping and Bacterial Genetics - Practice Quiz

1 Linkage refers to the tendency of genes located on the same chromosome to:

2 The term 'linkage' was first coined by:

3 Complete linkage occurs when linked genes:

4 Incomplete linkage results in the formation of:

5 Complete linkage was first demonstrated in male:

6 Crossing over involves the exchange of segments between:

7 The X-shaped structure formed at the site of crossing over is called a:

8 Crossing over takes place during which stage of meiosis?

9 The enzyme responsible for joining exchanged DNA segments during crossing over is:

10 One map unit (centimorgan) is equal to:

11 The distance between two genes on a chromosome map is measured by:

12 A three-point test cross is used to determine the:

13 In a three-point cross, the least frequent progeny classes represent:

14 Tetrad analysis is commonly performed using:

15 The four haploid products of a single meiosis in fungi are collectively called a:

16 Bacterial transformation involves the uptake of:

17 Transformation was first demonstrated in bacteria by:

18 In transduction, bacterial genes are transferred from one cell to another by a:

19 Bacterial conjugation requires direct contact between cells through a:

20 In conjugation, the donor bacterium carrying the fertility factor is called:

21 Two genes located map units apart on the same chromosome will produce recombinant and parental gametes in what approximate ratio?

22 In Drosophila, why is complete linkage observed only in males and not in females?

23 According to the Holliday model, the exchange of genetic material between homologous chromosomes involves an intermediate structure known as the:

24 In a two-point testcross, parental and recombinant offspring are obtained out of total. What is the map distance between the two genes?

25 In a three-point testcross, the double crossover progeny are identified because they occur in which frequency class?

26 If single crossover frequencies between A–B and B–C are and , and observed double crossovers are , what is the coefficient of coincidence?

27 Interference of in a three-point cross indicates that:

28 In Neurospora, second-division segregation patterns in an ordered tetrad indicate that:

29 In tetrad analysis, if the number of parental ditype (PD) tetrads greatly exceeds nonparental ditype (NPD) tetrads, the two genes are:

30 Using tetrad data, the map distance formula is expressed as: map distance

31 In bacterial transformation mapping, two genes are considered closely linked if they are:

32 In a transformation experiment, genes A and B are co-transformed at high frequency while B and C are rarely co-transformed. This suggests:

33 In generalized transduction, co-transduction frequency between two genes is used to map them. A higher co-transduction frequency indicates the genes are:

34 Which type of transduction is characterized by a phage picking up only specific bacterial genes located adjacent to its integration site?

35 If genes X and Y show a co-transduction frequency of and genes Y and Z show , which pair is more closely linked?

36 In an interrupted mating experiment using an Hfr strain, the order of gene transfer is determined by:

37 An Hfr strain is formed when:

38 In interrupted mating, genes A, B, and C enter the recipient at , , and minutes respectively. Which gene is closest to the origin of transfer?

39 In incomplete linkage, the appearance of recombinant offspring in a testcross is directly due to:

40 During meiotic recombination, the enzyme that initiates crossing over by creating double-strand breaks in DNA is:

41 In a three-point testcross involving genes , , and , the parental classes are the most frequent and the double-crossover (DCO) classes show that the gene allele is exchanged relative to parentals. If parentals are and , and the DCOs are and , which gene is located in the middle?

42 A three-point testcross yields the following DCO frequency of , and single crossover frequencies between the flanking regions of and . What is the coefficient of coincidence?

43 In a three-point cross, map distances calculated between the outer markers are often smaller than the true physical distance. What is the primary reason for this underestimation?

44 In an ordered tetrad analysis of two linked genes, a cross yields Parental Ditype (PD) , Non-Parental Ditype (NPD) , and Tetratype (TT) . What is the map distance between the two genes (in map units)?

45 In ordered tetrads of Neurospora, second-division segregation (MII) patterns arise from crossovers between a gene and its centromere. If MII asci frequency is , what is the gene-to-centromere distance?

46 When two genes are unlinked, tetrad analysis predicts a specific relationship among tetrad types. Which condition confirms independent assortment?

47 In the double-strand break repair (DSBR) model of recombination, resolution of the double Holliday junction can yield crossover or non-crossover products. What determines whether a crossover results?

48 Gene conversion, a non-reciprocal transfer of genetic information, is best explained by which molecular event during recombination?

49 In Drosophila, complete linkage is observed only in one specific situation. Which of the following explains why crossing over is absent in males?

50 Two genes are map units apart on the same chromosome. What recombination frequency and genetic behavior would you expect to observe in a testcross?

51 In an interrupted mating experiment with an Hfr strain, the time of entry of a gene into the recipient is used for mapping. If gene enters at min and gene enters at min, what does this indicate?

52 Different Hfr strains transfer chromosomal markers in different orders and directions. This observation is best explained by which feature of the bacterial chromosome?

53 In a generalized transduction cotransduction experiment, two genes are cotransduced at a frequency of . Using the Wu formula, cotransduction frequency where is the length of transducing DNA. What does a high cotransduction frequency indicate?

54 Specialized transduction differs from generalized transduction in a fundamental way. Which statement correctly describes specialized transduction?

55 In bacterial transformation mapping, two markers are cotransformed at high frequency. What must be true for two genes to be cotransformed?

56 In a transformation experiment, genes and show cotransformation, and and show cotransformation, but and are never cotransformed. What is the most likely gene order?

57 Given a two-point testcross with progeny where recombinants total , but you suspect undetected double crossovers, how would the true map distance compare to the calculated m.u.?

58 A dihybrid (cis configuration, genes linked) is testcrossed. If linkage is incomplete with recombination, what proportion of offspring will be recombinant type ?

59 Chiasmata observed cytologically during diplotene are physical manifestations of crossing over. Which statement about the relationship between chiasma frequency and recombination is correct?

60 In an F F cross, why are chromosomal genes transferred at very low frequency compared to an Hfr F cross?