EXAM. #2: MULTIPLE CHOICE QUESTIONS WITH ANSWERS PDF

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MULTIPLE CHOICE 100+ questions with correct answers// great for self testing and recalling information for the exam...

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1. A mutation in a gene often results in a reduction of the product of that gene. The term for this type of mutation is

 Loss of function or null (in the case of complete loss) 2. Which mutations are generally dominant since one copy in a diploid organism is sufficient to alter the normal phenotype?

 Gain of function 3. Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A, such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual. If heterozygotes are phenotypically normal, we would say that the mutant allele is ________ to its normal allele.

 Recessive 4. What is the most prevalent form of an allele called?

 Wild type 5. Which of the following is true?

 A neutral mutation leads to no discernable phenotype 6. A gain-of-function mutation _______.

 Results in an increased quantity of the normal gene product 7. Typically, when one wishes to represent a gene, the symbol used is _________.

 In italics 8. Assume that a cross is made between two organisms that are both heterozygous for a gene that shows incomplete dominance. What phenotypic and genotypic ratios are expected in the offspring?

 Phenotypic 1:2:1; genotypic 1:2:1 9. The trait of medium-sized leaves in iris is determined by the genetic condition Pp. Plants with large leaves are PP, whereas plants with small leaves are pp. A cross is made between two plants each with medium-sized leaves. What is the term for this allelic relationship?

 Incomplete dominance 10. The trait of medium-sized leaves in iris is determined by the genetic condition Pp. Plants with large leaves are PP, whereas plants with small leaves are pp. A cross is made between two plants each with medium-sized leaves. If they produce 80 seedlings, what would be the expected phenotypes, and in what numbers would they be expected?

 20 (large leaves), 40 (medium leaves), 20 (small leaves)

11. The following coat colors are known to be determined by alleles at one locus in horses: palomino = golden coat with lighter mane and tail cremello = almost white chestnut = brown The following table gives ratios obtained in matings of the above varieties: Cross 1 2 3 4

Parents cremello x cremello chestnut x chestnut cremello x chestnut palomino x palomino

Offspring all cremello all chestnut all palomino 1/4 = chestnut 1/2 = palomino 1/4 cremello Assign gene symbols for the genetic control of coat color on the basis of these data.

 C1C1 = cremello, C2C2 = chestnut, C1C2 = palomino 12. What is the difference between incomplete dominance and codominance?

 In codominance, both phenotypes are expressed in heterozygotes. In incomplete dominance, the heterozygote shows a phenotype that is intermediate between the two homozygotes. 13. What is the blood type of individuals who cannot add the terminal sugar to the H substance?  O 14. A situation in which there are more than two alternative forms of a given gene would be called ________.

 Multiple alleles 15. In mice, there is a set of multiple alleles of a gene for coat color. Four of those alleles are as follows: C = full color (wild type) cch = chinchilla cd = dilution c = albino

Given that the gene locus is not sex-linked, and that each allele is dominant to those lower in the list, give the phenotypic ratios expected from the following cross. chinchilla (heterozygous for albino) × albino

 1 chinchilla :1 albino 16. In a mating between individuals with the genotypes IAi × ii, what percentage of the offspring are expected to have the O blood type?

 50% 17. In a mating between individuals with the genotypes IAIB × ii, what percentage of the offspring are expected to have the O blood type?

 0% 18.The ABO blood group locus in humans provides an example of ________.  Multiple alleles 19. Why can multiple alleles only be studied in populations?

 Any individual diploid organism can have, at most, two different alleles at a single locus. 20. What would be a typical phenotypic monohybrid ratio in which a lethal allele is involved?  2:1 21. Which of the following statements is always true when mutations occur in genes whose products are essential to an organism's survival?

 A homozygote for a recessive lethal allele will not survive. 22. What term is used to express the idea that several genes exert influence over the same characteristic?  Gene interaction 23. A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.  Epistasis 24.Typical ratios resulting from epistatic interactions in dihybrid crosses would be_

 9:3:4, 9:7 25. In the mouse, gene A allows pigmentation to be deposited in the individual coat hairs; its allele a prevents such deposition of pigment, resulting in an albino. Gene B gives agouti (wild-type fur); its allele b gives black fur. What would the expected ratio of the progeny be in a cross of a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse?

 1 (agouti) :1 (black) : 2 (albino) 26. The following F2 results occur from a typical dihybrid cross: purple: A_B_ 9/16 white: aaB_ 3/16 white: A_bb 3/16 white: aabb 1/1 If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb), what phenotypic ratio is expected in the offspring?

 1 purple : 3 white 27.Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Assume that two fully heterozygous plants are crossed. Give the phenotypes (with frequencies) of the offspring.

 12 white : 3 yellow : 1 green 28. Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Crosses among heterozygotes give a 12:3:1 ratio. What type of gene interaction would account for these results?

 Epistasis 29.Alleles that are masked by an epistatic locus are said to be ________ to the genes at that locus.

 Hypostatic 30. Multiple mutations that are found to be present in a single gene are said to belong to the same ________ group.

 Complementation 31. Which of the following crosses would indicate that the mutants were in the same complementation group?

 Pink eye fly × pink eye fly -> pink eye fly 32. Complementation analysis is used to determine _______.

 Whether two mutations that produce the same phenotype reside in the same or different genes 33.What is the term for a gene mutation that leads to a myriad of disparate effects?  Pleiotropy 34. With which of the following would hemizygosity most likely be associated?

 X-linked inheritance

35. Because of the mechanism of sex determination, males of many species can be neither homozygous nor heterozygous. Such males are said to be __.

 Hemizygous 36. The white-eyed gene in Drosophila is recessive and sex-linked. Assume that a white-eyed female is mated to a wild-type male. What would be the phenotypes of the offspring?  Females’ wild type, males white eyed 37. Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first son will have hemophilia?

 1/2 38. The deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD) is inherited as a recessive gene on the X chromosome in humans. A phenotypically normal woman (whose father had G6PD) is married to a normal man. What fraction of their sons would be expected to have G6PD?  1/2 39. Which of the following is an example of sex-limited inheritance?  Beard formation in humans 40. A gene in which the heterozygous condition is displayed differently in males and females is referred to as _______.

 Sex-influenced 41. A ________ is one whose expression is influenced by some environmental condition.  Conditional mutant 42. What is a significant difference between X-linked and sex-influenced inheritances?

 In X-linked inheritance, the gene in question is on the X chromosome; in sex-influenced inheritance, the gene is autosomal 43. What ratio is obtained when platinum foxes are interbred?

 2/3 platinum, 1/3 silver Is the P allele behaving dominantly or recessively in causing lethality?

 Recessively Is the P allele behaving dominantly or recessively in causing platinum coat color?

 Dominantly 44. What term is applied when two genes fail to assort independently, that is, they tend to segregate together during gamete formation?

 Linkage 45. Which of the following statements is true?

 If two gene loci are on nonhomologous chromosomes, genes at these loci are expected to assort independently. 46. A ____ is all the genes on a single chromosome.

 Linkage group 47. If complete linkage occurs, we expect

 To see only parental phenotypes in the F2 of the appropriate test cross 48. Assume that a cross is made between AaBb and aabb plants and that the offspring fall into approximately equal numbers of the following groups: AaBb, Aabb, aaBb, aabb. These results are consistent with the following circumstance:

 Independent assortment. 49. Which of the following scenarios would erroneously lead you to believe two genes reside on different chromosomes when they in fact are on the same chromosome?  The genes are very far apart on the same chromosome, such that there is always a crossover between them 50. Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb, 48 Aabb, 52 aaBb, 94 aabb. These results are consistent with the following circumstance:

 Linkage with approximately 33 map units between the two gene loci. 51. Who was the student in Morgan's laboratory who first realized that the sequence of genes could be determined by Morgan's proposal that two genes located relatively close to each other are less likely to form chiasma between them than if the two genes were relatively far apart?

A. H. Sturtevant 52. At what stage of the meiotic cell cycle and during what chromosomal configuration does crossing over occur?

 At the four-strand stage of meiosis, after synapsis of homologous chromosomes, and before the end of prophase I 53. What is the relationship between the degree of crossing over and the distance between two genes?

 It is direct: as the distance increases, the frequency of recombination increases. 54. The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103. From these data, one can conclude that _

The G and E loci are linked 55. The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103. From these data one can conclude that

 The recombinant progeny are gE/ge and Ge/ge 56. When Morgan carried out crosses involving two X-linked genes in Drosophila, he sometimes observed new phenotypes that were not present in the parents. What did Morgan propose from these observations?

 The points of overlap between synapsed homologous chromosomes, called chiasmata, were points of genetic exchange. 57. Crossing over during prophase I of meiosis occurs between alleles on sister chromatids

 False Which of the following statements about gamete formation during meiosis is false? Parental gametes can be formed only if there is no crossing over during meiosis. If two genes on the same chromosome exhibit complete linkage, what is the expected F2 phenotypic ratio from a selfed heterozygote with the genotype a + b + ⁄⁄ ab?

 3:1 58. The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103. From these data, one can conclude that there are ________ map units between the G and E loci.

 20 59. Phenotypically wild-type F1 female Drosophila, whose mothers had light eyes (lt) and fathers had straw (stw) bristles, produced the following offspring when crossed to homozygous light-straw males: Numbe Phenotype r light-straw 22 wild-type 18 light 970 straw 970 Total: 2000 Compute the map distance between the light and straw loci.

 2 map units 60. In a three-point mapping experiment, which class do you expect to find the least?

 Double crossover

61. In a three-point mapping experiment, how many different genotypic classes are expected?

 8 62. How can the order of three linked genes (A, B, and C) on the same chromosome be determined?

 Look for double-crossover phenotypes involving the wild-type and mutant alleles of genes A, B, and C. 63. To construct a mapping cross of linked genes, it is important that the genotypes of some of the gametes produced by the heterozygote can be deduced by examining the phenotypes of the progeny.  FALSE. In a three-point mapping experiment for the genes y-w-ec, the following percentages of events are observed: NCO events: 65%; SCO events between y and w: 15%; SCO events between y and ec: 17%; DCO events: 3% What is the map distance between y and ec?

 20 map units For linked genes A, B, and C, the map distance A–B is 5 map units and the map distance B–C is 25 map units. If there are 10 double crossover events out of 1000 offspring, what is the interference?

 0.2 64. The phenomenon in which one crossover decreases the likelihood of crossovers in nearby regions is called

 Positive interference 65. Assume that two genes are 80 map units apart on chromosome II of Drosophila and that a cross is made between a doubly heterozygous female and a homozygous recessive male. What percent recombination would be expected in the offspring of this type of cross?

 50 66. Which of the following best describes why mapping is most accurate when genes are close together on a chromosome?

 Double crossover events yield a result that looks the same as no crossover in a two gene mapping experiment and this throws off the calculations. 67. The coefficient of coincidence reflects the frequency of observed double crossovers compared to the frequency of expected double crossovers. What is the relationship between the coefficient of coincidence and interference?

 Interference is one minus the coefficient of coincidence

68. _______ occurs when a crossover in one region of a chromosome reduces crossovers in nearby regions.

 Positive interference 69. What two terms apply to the fusion of cultured human and mouse cells that produces cell lines that are useful in assigning a gene to a particular human chromosome?

 Heterokaryon and synkaryon 70. What is a lod score?

 Determination of the probability that two traits are linked by analyzing pedigrees 71. Lod scores are used to predict which of the following?

 Gene linkage 72. Somatic cell hybridization analysis can be used to _

 Assign human genes to the chromosomes on which they reside 73. Methods for determining the linkage group and genetic map in humans involve which of the following?

 DNA markers 74. What relatively recent scientific advancement has made mapping by linkage or classical genetic mapping approaches virtually obsolete?

 The genome sequence of a species 75. Which of the following DNA markers CANNOT be used for mapping?

 Chiasmata 76. Based on the classic experiments of Creighton and McClintock with maize, crossing over involves a physical exchange between chromatids. What particular chromosomal characteristic allowed their experiments to succeed?

 A chromosome with a unique cytological marker 77. What is the evidence that Chiasmata are points of physical exchange between chromatids?

 Cytological markers such as knobs and translocations have been used to show that there is a physical exchange in chromosome arms during meiosis. 78. Sister chromatid exchanges increase in frequency in the presence of X-rays, certain viruses, ultraviolet light, and certain chemical mutagens. In what autosomal recessive disorder is there known to be an increase in sister chromatid exchanges?

 Bloom syndrome 79. Why does crossing over occur more often between two distantly linked genes than between two closely linked genes on the same chromosome?

 Crossing over is somewhat randomly distributed over the length of the chromosome. Two loci that are far apart are more likely to have a crossover between them than two loci that are close together. 80. Why are double-crossover events expected less frequently than single-crossover events?

 The probability of two crossover events occurring at the same time is much lower than the probability of one. 81. What possible conclusions can be drawn from the observations that in male Drosophila, no crossing over occurs, and that during meiosis, synaptonemal complexes are not seen in males but are observed in females where crossing over occurs?

 The synaptonemal complex is required for crossing over 82. What are DNA markers?

 DNA markers are unique DNA sequences whose sequence and chromosomal location are known...