Gene mapping – linkage maps, molecular markers, somatic cell hybrids - Question Bank

1. What is the main challenge in constructing a high-resolution physical map of an entire genome?
A) Lack of polymorphic markers.
B) The sheer size of the genome and the need to assemble large DNA fragments accurately.
C) Difficulty in obtaining DNA samples.
D) The high cost of linkage analysis.
2. Which of the following statements about molecular markers is true?
A) All molecular markers are co-dominant.
B) Molecular markers are always dominant.
C) Molecular markers detect variations in DNA sequences.
D) Molecular markers are only useful for mapping genes in humans.
3. The process of creating a linkage map typically involves analyzing the inheritance patterns of alleles in:
A) Single somatic cells.
B) A population of related individuals (pedigree) or mapping populations (e.g., F2, recombinant inbred lines).
C) A single generation of offspring.
D) Non-living DNA samples.
4. What is a 'radiation hybrid' panel used for?
A) To map genes based on recombination frequencies.
B) To generate cell lines with random fragments of one genome integrated into another, aiding in physical mapping.
C) To study gene expression.
D) To induce mutations.
5. Which type of map is generally considered more accurate for determining the precise location of genes?
A) Linkage map
B) Cytogenetic map
C) Physical map
D) Phenotypic map
6. What is the primary advantage of using molecular markers over phenotypic markers for gene mapping?
A) Phenotypic markers are more abundant.
B) Molecular markers are not affected by environmental factors and can be identified throughout the life cycle.
C) Phenotypic markers are easier to observe.
D) Molecular markers only work for dominant traits.
7. Which of the following is NOT a direct output of linkage mapping?
A) Gene order
B) Relative distances between genes
C) Physical locations of genes on DNA
D) Identification of linked genes
8. What is a 'translocation' in the context of chromosomes?
A) The exchange of segments between homologous chromosomes.
B) The movement of a chromosome segment from one chromosome to a non-homologous chromosome.
C) The complete absence of a chromosome.
D) The duplication of an entire chromosome.
9. In somatic cell hybridization, the loss of chromosomes from one species (e.g., human) is often a result of:
A) Cellular fusion.
B) Preferential segregation during mitosis in the hybrid cell.
C) DNA replication.
D) Meiotic recombination.
10. SNP markers are useful because they are:
A) Abundant, highly polymorphic, and can be genotyped rapidly.
B) Always co-dominant.
C) Only found in non-coding regions of DNA.
D) Difficult to detect and require large DNA samples.
11. What is a Single Nucleotide Polymorphism (SNP)?
A) A variation in the number of tandem repeats.
B) A variation in DNA sequence at a single nucleotide position.
C) A difference in restriction enzyme cutting sites.
D) A change in the length of a DNA fragment.
12. Which type of marker is often generated by PCR using short, repeated DNA sequences as primers?
A) RFLP
B) SNP
C) SSR
D) AFLP
13. During meiosis, homologous chromosomes can exchange segments. This process is known as:
A) Mitosis
B) Replication
C) Crossing over
D) Fertilization
14. What is a 'diploid' organism in the context of genetics?
A) An organism with a single set of chromosomes.
B) An organism with two complete sets of chromosomes.
C) An organism that reproduces asexually.
D) An organism with more than two sets of chromosomes.
15. The phenomenon where genes on the same chromosome are inherited together more often than expected by chance is called:
A) Independent assortment
B) Segregation
C) Linkage
D) Epistasis
16. What does it mean for two genes to be 'linked'?
A) They are located on the same chromosome and tend to be inherited together.
B) They have identical DNA sequences.
C) They control the same trait.
D) They are located on different chromosomes and assort independently.
17. Which of the following is a potential challenge when constructing a linkage map?
A) Ensuring markers are polymorphic and informative.
B) The high cost of sequencing.
C) The need for specialized hybrid cells.
D) The limited number of available DNA markers.
18. What is a 'contig' in the context of physical mapping?
A) A region of a chromosome where genes are tightly linked.
B) A set of overlapping DNA fragments that represent a continuous stretch of genomic DNA.
C) A type of genetic marker.
D) A hybrid cell line.
19. FISH is primarily used for:
A) Determining recombination frequencies.
B) Assigning genes to specific chromosomal bands or regions (physical mapping).
C) Detecting single nucleotide polymorphisms.
D) Measuring gene expression levels.
20. Which technique uses labeled DNA probes that hybridize to specific locations on chromosomes, often visualized under a microscope?
A) Southern blotting
B) Northern blotting
C) Western blotting
D) Fluorescence In Situ Hybridization (FISH)
21. What is a limitation of using linkage mapping to map genes that are very close together?
A) Recombination events are too frequent.
B) Recombination events are too rare to be reliably detected.
C) The genes assort independently.
D) The genes are always on different chromosomes.
22. Which method is commonly used to create high-density genetic maps with thousands of markers?
A) Pedigree analysis of a few individuals.
B) Somatic cell hybridization.
C) High-throughput sequencing and genotyping (e.g., SNP arrays, whole-genome sequencing).
D) Classical linkage analysis with a small number of RFLPs.
23. What is a 'marker' in the context of gene mapping?
A) A gene with a known function.
B) A DNA sequence with a known location that can be identified.
C) A phenotypic trait.
D) A type of chromosome abnormality.
24. Which molecular marker technique is often considered 'co-dominant' because it can distinguish between homozygous and heterozygous individuals?
A) RAPD
B) SSR
C) RFLP
D) All of the above
25. What is the term for a specific location on a chromosome where a gene or marker is found?
A) Allele
B) Locus
C) Genotype
D) Phenotype
26. Which of the following statements about linkage maps and physical maps is FALSE?
A) Linkage maps are based on recombination frequencies, while physical maps are based on DNA sequences or physical distances.
B) Distances on linkage maps are measured in centimorgans, while distances on physical maps are measured in base pairs.
C) Genes located far apart on a chromosome always show high recombination frequencies on linkage maps.
D) Physical maps provide a more accurate representation of gene order than linkage maps.
27. What type of information does a physical map primarily provide?
A) Recombination frequencies between genes.
B) The actual physical distance between genes on a chromosome.
C) The inheritance pattern of genes.
D) The rate of mutation.
28. What type of information does a linkage map primarily provide?
A) The physical location of genes on DNA.
B) The order and relative distances between genes based on inheritance patterns.
C) The DNA sequence of genes.
D) The functional role of genes.
29. The loss of specific human chromosomes from a somatic cell hybrid line, coupled with the retention of a specific human enzyme activity, suggests:
A) The gene for the enzyme is located on a different chromosome.
B) The gene for the enzyme is located on the lost chromosome.
C) The gene for the enzyme is located on the retained chromosome.
D) The enzyme is produced by the rodent cell.
30. What is the main advantage of using somatic cell hybrids for gene mapping?
A) It allows for high-resolution mapping of closely linked genes.
B) It can assign genes to entire chromosomes or large chromosomal segments.
C) It is a rapid and inexpensive method.
D) It directly measures recombination frequencies.
31. How are genes assigned to specific chromosomes using somatic cell hybrids?
A) By observing the phenotype of the hybrid cells.
B) By analyzing the presence or absence of specific human enzymes (encoded by known genes) in hybrid cells that have lost specific human chromosomes.
C) By sequencing the DNA of the hybrid cells.
D) By inducing mutations in the hybrid cells.
32. In human-rodent somatic cell hybrids, what is the typical outcome regarding chromosomes?
A) Human chromosomes are preferentially retained.
B) Rodent chromosomes are preferentially retained.
C) All human chromosomes are retained.
D) No chromosomes are retained.
33. What is a key application of somatic cell hybridization in gene mapping?
A) To determine the order of genes on a chromosome.
B) To assign genes to specific chromosomes or chromosome regions.
C) To measure recombination frequencies.
D) To identify single nucleotide polymorphisms.
34. Somatic cell hybridization involves:
A) Fusion of gametes from different species.
B) Fusion of somatic cells from different individuals or species.
C) Replication of somatic cells in vitro.
D) Isolation of somatic chromosomes.
35. Which technique directly measures the physical distance between DNA markers?
A) Linkage analysis
B) Fluorescence In Situ Hybridization (FISH)
C) Pedigree analysis
D) Quantitative Trait Loci (QTL) mapping
36. A physical map represents gene locations based on:
A) Recombination frequencies.
B) Actual physical distances on the DNA molecule.
C) Phenotypic traits observed.
D) Protein expression levels.
37. What is the primary advantage of SSR markers over RFLP markers?
A) They require less DNA.
B) They are generally more polymorphic and co-dominant.
C) They are easier to design and less expensive.
D) They provide direct information about DNA sequence.
38. What is a limitation of RAPD markers?
A) Requires large amounts of DNA.
B) Low reproducibility due to sensitivity to reaction conditions.
C) High cost of primers.
D) Limited polymorphism across populations.
39. Which molecular marker technique involves digestion of DNA with restriction enzymes, ligation of adaptors, and selective amplification by PCR?
A) RFLP
B) RAPD
C) SSR
D) AFLP
40. Microsatellites (SSRs) are characterized by:
A) Single nucleotide variations.
B) Variable numbers of short tandemly repeated DNA sequences.
C) Differences in restriction enzyme digestion patterns.
D) Large insertions or deletions.
41. Which molecular marker technique utilizes PCR to amplify anonymous DNA fragments, with primer concentration being crucial?
A) RFLP
B) RAPD
C) SSR
D) AFLP
42. RFLP markers are based on variations in:
A) DNA sequence length amplified by PCR.
B) The number of tandem repeats at specific loci.
C) Restriction enzyme cutting sites.
D) Protein electrophoretic mobility.
43. Which of the following is NOT a type of molecular marker used in gene mapping?
A) Restriction Fragment Length Polymorphism (RFLP)
B) Random Amplified Polymorphic DNA (RAPD)
C) Microsatellites (Simple Sequence Repeats - SSR)
D) Mitochondrial DNA Sequencing (mtDNA)
44. What does a high recombination frequency between two genes suggest?
A) The genes are located very close to each other on the chromosome.
B) The genes are located far apart on the same chromosome or on different chromosomes.
C) The genes are linked and do not assort independently.
D) The genes are identical and have no alleles.
45. A recombination frequency of 1% between two genes corresponds to a distance of:
A) 1 base pair
B) 1 megabase pair
C) 1 centimorgan
D) 1 kilobase pair
46. What is the unit of genetic distance in a linkage map?
A) Base pairs (bp)
B) Megabase pairs (Mbp)
C) Centimorgan (cM)
D) Kilobase pairs (kbp)
47. In linkage mapping, what phenomenon is used to determine the distance between genes?
A) Independent assortment
B) Crossing over (recombination)
C) Segregation of alleles
D) Polyploidy
48. Which type of map represents the linear arrangement of genes on a chromosome based on recombination frequencies?
A) Physical map
B) Linkage map
C) Cytogenetic map
D) Restriction map
49. What is the primary purpose of gene mapping?
A) To determine the exact nucleotide sequence of a genome.
B) To locate the relative positions of genes on chromosomes.
C) To identify all the proteins produced by an organism.
D) To analyze the evolutionary history of a gene.
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