ZOOL/BOT 3333

GENETICS Exam #2

The answers to the practice exam are found here, but please work the practice exam first!

A. True/False and multiple choice questions (2 points each). Please fill in your answers on the scantron sheets provided. For true/false questions, please indicate whether a statement is true (1) or false (2), or, for multiple choice questions, circle the letter representing the single best choice. If a question seems ambiguous to you, please raise your hand and I will try to clarify the source of ambiguity.

1. In snapdragons, a cross between pure breeding red- and white-flowered plants produces all pink progeny. Crossing F2 individuals produces a ratio of 1 red: 2 pink: 1 white. This represents an example of:
   a) incomplete dominance; b) reduced penetrance; c) phenocopy; d) complementary gene action at two gene loci; e) lethal genes.
2. Two independently derived pure breeding lines of peas produce white petal flowers. When these two lines are crossed, however, all the F1 progeny have purple flowers. The F2 plants show both purple and white plants in a ratio of 9:7. This is an example of:
   a) incomplete dominance; b) reduced penetrance; c) phenocopy; d) complementary gene action at two gene loci; e) lethal genes.
3. The idea that genes control the ability to produce enzymes was first suggested from observations in which organism?
   a) pea plants; b) fruit flies; c) E. coli; d) mice; e) humans.
4. True or false. Abnormal chromosome segregation resulting in aneuploidy occurs only during meiosis.
   
5. Which of the following HLA genotypes would allow a man to be excluded as the father of a child with an HLA genotype of A1,A11;B8,B12?
   a) A1,A11;B7;B15; b) A3,A11;B27,B8; c) A1,A11;B8;Bw41; d) A1,A1;B8,B8; e) A2,A11;B12,B37.
6. Which of the following most accurately summarizes the phenotype of a human with a XXY complement of sex chromosomes?
   a) normal male; b) normal female; c) abnormal male; d) abnormal female; e) inviable embryo.

Questions 7-8 pertain to the following. In a certain plant species, an F2 generation produced 113 round seeds, 75 oval seeds, and 12 curled seeds. One of the original homozygous parent strains had round seeds, and the other had curled seeds.

7. True or false. All of the 12 curled F2 progeny would be expected to breed true if crossed to the curled parental strain.
8. The genotype of the 75 F2 oval seeds could be represented as: a) aa; b) AaBb; c) aaBb; d) aabb; e) none of the above.
9. If a normal man marries a woman who is heterozygous for a sex-linked recessive lethal mutation, what would be the expected sex ratio of their offspring?
   a) equal numbers of males and females; b) 3 females: 1 male; c) 2 females: 1 male; d) only females; e) only males.
10. True or false. Women who are 40 years of age are twice as likely to have a Down syndrome child as women who are 20 years of age.
11. The gene for the enzyme superoxide dismutase II is located at band 1 in region 2 on the long arm of chromosome 6. This would be abbreviated:
    a) 21p6; b) 21q6; c) 6p21; d) 6q21; e) none of the above.
12. True or false: All genes located on the same chromosome must be within 50 map units of one another.
13. In Drosophila, the yellow (body color) gene locus is located 1.5 cM away from the white (eye color) gene locus. In a female heterozygous for both recessive gene loci, what fraction of the gametes would be expected to have a undergone a crossover between these genes?
    a) 0.015; b) 0.03; c) 0.15; d) 0.3; e) none of the above.
14. In analyzing a human karyotype:
    a) test results can be obtained in several hours, using mitotic cells taken directly from blood; b) all chromosomes are easily identified simply on the basis of size and centromere position; c) colchicine is added to arrest cells in metaphase; d) all of the above; e) none of the above.
15. The telomere of a chromosome refers to:
    a) a specialized region at the ends of a chromosome; b) the site where the spindle fibers attach to a chromosome; c) the site where crossing over has occurred; d) the primary constriction; e) the secondary constriction.
16. The successful mapping of a gene to a human chromosome by somatic cell hybridization requires that:
    a) the parental cells will be preferentially killed in a selective media; b) human chromosomes are randomly lost from the hybrid cells; c) the human gene products can be identified in hybrid cells; d) all of the above; e) none of the above.
17. In Neurospora, a first division segregation pattern:
    a) represents a single crossover between a gene and the centromere; b) identifies a recombinant ascus; c) will produce non-parental ditype asci; d) all of the above; e) none of the above.
18. True or false. The Delbruck-Luria fluctuation test is a probability technique designed to aid in assembling linkage information from human pedigree data.
19. True or false. In most organisms, mutation rates are harder to measure than mutation frequencies.
20. The results of an analysis of five human-mouse hybrids are given in the table below, representing the human chromosomal content of each clone. (+ = chromosome present; - = chromosome absent). If the enzyme malate dehydrogenase is present in clone B but absent in A, C, D and E, the gene for this enzyme is found on chromosome:
    a) 2; b) 3; c) 9; d) 10; e) 14.

B. Match and Identify (2 points each). Please match the following terms in part I with the appropriate definitions or specific examples given in part II. For each term, provide the single best answer; no term in part II should be used more than once. Please note that two circles must be filled for each answer.

part I.

21-2. pleiotropy
23-4. codominance
25-6. nucleolus organizer region
27-8. replica plating
29-30. linkage group
31-2. electrophoresis
33-4. bacteriophage
34-5. auxotroph
37-8. twin spot
39-40. ClB test

part II.

aa) chromosomal site that can serve as a landmark in cytogenetic analysis
bb) recessive epistasis
cc) mosaic arising from mitotic recombination
dd) multiple phenotypic effects resulting from a single gene locus
ee) technique used to identify protein polymorphisms
ab) an organism with wild-type nutritional requirements
ac) a technique used to identify X chromosomal lethal mutations in Drosophila
ad) genes that are located on the same chromosome
ae) demonstrated that mutations are not a result of physiological adaptation
ba) a type of virus
bc) requires supplemental nutrients relative to wild-type
bd) an inheritance pattern observed at ABO blood group locus
be) centromere
ca) a first division segregation pattern

C. Short Problems (15 points). Please answer the following problems. Be sure to show all work (eg. calculations); partial credit can only be assigned on the basis of work shown.

1. ( 7 points). In Neurospora, a cross is made between individuals off the genotypes aB and Ab. The following one hundred ordered tetrads are obtained:

<-----------TYPES OF ASCI RECOVERED---------------------->

a) For tetrad analysis, what is the general observation that allows us to establish whether the two gene loci being tested are linked?

b) On the basis of the above data, are these two gene loci linked?

c) From the above data, estimate distance of the "A" gene locus from the centromere.

2. The following three recessive markers are known in lab mice: h, hotfoot; o, obese; and wa, waved. A trihybrid of unknown origin is testcrossed, producing the following offspring:

a) If the genes are linked, determine the relative order and the map distances between them.

b) What was the cis-trans allele arrangement in the trihybrid parent?

c) Is there crossover interference? If yes, how much?

Updated: September 25, 1997
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