HMB265H Midterm 2
Monday February 23, 2004; 6:00 – 8:00 pm
Duration 2 hours; aids allowed
1. What is the term for the specific set of alleles carried by an individual?
A) genotype
B) phenotype
C) homolog
D) genome
E) diploid
2. Which of the following statements is true of dizygotic twins?
3. What are nonsense codons?
A) codons that code for multiple amino acids.
B) codons that code for no amino acids.
C) codons that can be read forward or backward.
D) codons that code for a suppressor
E) start codons.
4.The following diagram shows a protein-coding gene and specifies the positions of its
translational start and stop signals:
Which of the following is correct?
A) Upper is template strand, carboxy terminus of protein to right
B) Upper is template strand, carboxy terminus of protein to left
C) Lower is template strand, carboxy terminus of protein to right
D) Lower is template strand, carboxy terminus of protein to left
E) Either strand could be template on the basis of this information
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A) They are genotypically identical
B) They are phenotypically identical
C) They are derived from two fertilized eggs
D) They are derived from a single fertilized egg
E) Both B and C are true
5. What is the term for the association of separate amino acid chains to constitute one active protein?
A) Primary structure
B) Secondary structure
C) Tertiary structure
D) Quaternary structure
E) Quinternary structure
6. In the human genetic disorder alkaptonuria, urine turns black because of the presence of
homogentisic acid in individuals with the trait. What is this due to?
7. Consider the pathway for the synthesis of the amino acid arginine in Neurospora:
ARG-E
ARG-F
ARG-H
ornithine Æ citrulline Æ argininosuccinate Æ arginine
Mutant strains of Neurospora are grown in minimal media supplements as follows. Strains
may carry more than one mutation. Growth is shown by (+) no growth is shown by (o).
mutant
strain
a
nothing
o
Supplements
ornithine
citrulline
o
o
argininosuccinate
o
arginine
+
Indicate the most accurate statement regarding strain a.
A) There is a mutation in ARG-H; if citrulline accumulates, ARG-F is also defective.
B) There is a mutation in ARG-H; if ornithine accumulates, ARG-F is also defective.
C) There is a mutation in ARG-H; if argininosuccinate accumulates, ARG-F is also defective.
D) There is a mutation in ARG-H; if citrulline accumulates, ARG-E is also defective.
E) There is a mutation in ARG-E; if citrulline accumulates, ARG-F is also defective.
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A) the presence of large amounts of homogentisic acid in the diet.
B) failure of individuals with alkaptonuria to manufacture enzymes involved in the synthesis of
homogentisic acid.
C) failure of wild-type individuals to manufacture enzymes involved in the synthesis of
homogentisic acid.
D) failure of the kidneys to remove homogentisic acid from the urine.
E) failure of individuals with alkaptonuria to manufacture enzymes involved in the
breakdown of homogentisic acid.
8. Assume that a series of compounds has been discovered in Neurospora. Compounds A-F
appear to be members of an enzyme pathway. Several mutations have been identified and strains
1-4 each contain a single mutation. Shown below are 5 possible pathways. Choose the pathway
that best fits the data presented. [growth in minimal media with supplements is shown by (+), no
growth is shown by (o)]
strain
1
2
3
4
media supplement
A B C D E
o o o + o
o o o o o
o o o o +
o o + o o
F
o
+
+
o
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A) A Æ B Æ C Æ D Æ E Æ F
B) A Æ B Æ C Æ F Æ E Æ D
C) A Æ B Æ C Æ D
È
EÆF
D) A Æ B Æ C Æ D
È
EÆF
E) A Æ B Æ C Æ D
È
EÆF
9. What might the appearance of a novel phenotype resulting from a mutation be due to?
A) change in the amino acid sequence only.
B) change in the amount of protein expressed.
C) alteration in a gene that codes for a nontranslated RNA.
D) change in the developmental time or location at which a gene is expressed.
E) all of the above are possible consequences of a single base pair substitution.
10. If 35% of the bases in a region of the mouse genome are cytosine, what percentage in that
region are adenine?
A) 15%
B) 20%
C) 30%
D) 35%
E) none of the above
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11. In DNA, the 300Å fiber is formed into structural loops. Which protein is responsible for this?
A) histone H4
B) nucleosomase
C) histone H1
D) certain nonhistone proteins
E) telomerase
12. One function of a centromere is to contribute to proper chromosome segregation. What is the
other function?
13. Occasionally, a loss of function mutation may occur in the telomerase enzyme in a cell. What
is likely to be the result of this mutation on the DNA in the cell over the course of several rounds
of mitosis?
A) Chromosome length will gradually increase.
B) Chromosome length will gradually decrease.
C) Chromosome length will stay constant.
D) Chromosomes will fail to dissociate after replication.
E) None of the above
14. Where in DNA are most satellite sequences found?
A) chromosome arms.
B) telomeres.
C) centromeres.
D) spaces around the dark bands.
E) euchromatin
15. Which of the following statements is true about cells in the G0 stage?
A) they have two chromatids per chromosome.
B) they are replicating their chromosomes.
C) they are about to enter the mitotic phase of the cell cycle.
D) they are in an extended G1 phase and no longer cycling.
E) they are dead.
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A) hold sister chromatids together
B) ensure that proper chromosome arm length is maintained
C) allow easy karyotyping
D) meiotic chromosome replication
E) all of the above
16. The following is a list of mitotic events out of order.
a)
b)
c)
d)
e)
Chromosomes align on the midplate of the cell.
Kinetochores begin attaching to spindle fibers.
Nuclear membrane reforms, chromosomes decondense
Chromosomes condense, centrosomes migrate to opposite sides of nucleus.
Sister chromatids separate, move to opposite poles.
What is the correct order of events?
17. At which of the following stages of meiosis would homologous chromosomes be paired?
A) prophase of meiosis I
B) prophase of meiosis II
C) metaphase of meiosis I
D) metaphase of meiosis II
E) A and C are correct
18. What aspect of chromosome behavior most clearly accounts for Mendel's law of segregation?
A) Movement of sister chromatids to opposite poles at anaphase II of meiosis.
B) Movement of homologous chromosomes to opposite poles at anaphase I of meiosis.
C) Crossing over between homologous chromosomes during prophase I of meiosis.
D) Replication of chromosomes prior to meiosis.
E) Independent alignment of different homologous pairs on the metaphase I spindle.
19. Drosophila melanogaster has four pairs of chromosomes. Sperm from this species are formed
by a meiotic process in which homologous chromosomes pair and segregate but do not undergo
crossing over. How many genetically different kinds of sperm could be produced by a Drosophila
melanogaster male?
A) 4
B) 8
C) 16
D) 64
E) 256
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A) bdace
B) dabec
C) dbaec
D) abdce
E) edbac
20. In humans, XO individuals are females with Turner's syndrome and XXY individuals are
males with Klinefelter's syndrome. Which of the following events could not give rise to a
Klinefelter's male?
A) Nondisjunction at meiosis I in the mother.
B) Nondisjunction at meiosis II in the mother.
C) Nondisjunction at meiosis I in the father.
D) Nondisjunction at meiosis II in the father.
E) All of the above could give rise to a Klinefelter's male.
21. Among the dihybrid crosses below, which will give a 1:1:1:1 phenotypic ratio?
22. Sickle cell anemia is a recessive trait in humans. In a cross between a father who has sickle
cell anemia and a mother is heterozygous for the gene, what is the probability that their first
three children will be normal?
A) 1/4
B) 1/2
C) none
D) 1/8 = ½ x ½ x ½
E) 1/16
23. What is the characteristic progeny phenotype ratio for a selfed monohybrid?
A) 1:1
B) 1:2:1
C) 3:1
D) 9:3:3:1
E) 1:1:1:1
24. A rosy-eyed Drosophila was crossed with a forked Drosophila. The F1 were all wild-type
while the F2 consisted of 306 wild-type, 94 rosy-eyed, 102 fork-bristled and 33 forked-bristled
and rosy-eyed flies. What are the genotypes of the parents.
A) R/R ; F/F x r/r ; f/f
B) r/r ; F/F x R/R ; f/f
C) R/r ;F/f x R/r ; F/f
D) R/r ; F/f x r/r ; f/f
E) r/r ; F/f x R/r ; f/f
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A) AABB x aabb
B) AaBb x AaBb
C) AaBb x aabb
D) AaBB x aaBB
E) AAbb x aaBB
25. Calculate the probability of either all dominant or all recessive phenotypes for the alleles
A, B, E, and F in the following cross: AaBbccddEeFf x AaBbCcddEeFf
A) 0.0078
B) 0.0039
C) 0.32 =( ¾ x ¾ x ¾ x ¾ )+ (¼ x ¼ x ¼ x ¼ )
D) 0.16
E) 0.0020
26. Below is a pedigree of a human genetic disease in which stricken individuals are solidcolored. Apply the laws of probability and calculate the probability the offspring of the cousin
marriage 2 x 3 will have the disease.
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A) 1/16
B) 1/9
C) 1/6
D) ¼ = ½ x ½ (both are heterozygotes)
E) 4/9
27. Hemophilia is caused by an X-linked mutation in humans. If a woman whose paternal uncle
(father's brother) was a hemophiliac marries a man whose brother is also a hemophiliac, what is
the probability of their first child having hemophilia (note: assume no other hemophilia in the
pedigree and no hidden carriers).
A) 0 (woman’s father is normal so she can’t have the allele)
B) 1/4
C) 1/2
D) 1/8
E) 1
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28. Individuals with an XXY karyotype are ______ in humans and ______ in fruit flies.
A) male, male
B) male, female
C) female, male
D) female, female
E) male, intersexual
29. Color vision depends upon the dominant alleles of three genes — the R gene and the G gene
are both on the X chromosome, while the B gene is autosomal. Recessive mutations in any of
the three genes can cause color-blindness. Suppose a colorblind man marries a colorblind
woman and all of their offspring have normal vision. What is the genotype of the woman?
30. In the following pedigree, the indicated trait is caused by what type of allele?
A) autosomal recessive
B) autosomal dominant
C) X-linked recessive
D) X-linked dominant
E) Y-linked
31. Which of the following ratios indicates a lethal gene?
A) 2:1
B) 3:1
C) 1:2:1
D) 1:1
E) 4:1
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A) RRGGbb
B) RRggBB
C) rrGGbb
D) RRggBB or RRGGbb
E) rrGGbb or rrggBB
32. What is the term for genes with more than one wild-type allele?
A) incomplete dominance.
B) penetrance and expressivity.
C) pleiotropic.
D) polymorphic
E) dihybrid.
33. The blood groups A, B and O show:
34. In a certain breed of plants, dark green is determined by the dominant gene “G” and light
green is determined by the recessive gene “g”. The heterozygote shows 75% penetrance and
will look phenotypically light green. If the parental cross is GG x gg; what phenotypes would
be observed in a population of 400 F2 plants?
A) 300 dark green, 100 light green
B) 100 dark green, 200 medium green, 100 light green
C) 250 dark green, 150 light green (this is correct but the wording is confusing; 75% of Gg
heterozygotes are the expected dark green while the rest are light green instead)
D) 150 dark green, 250 light green
E) 100 dark green, 300 light green
35. Coat color in a certain species of rabbit is governed by multiple alleles. The hierarchy with
reference to dominance for these alleles are as follows: Colored (c+), Chinchilla, (cch),
Himalayan (ch) and Albino (c). What is
the phenotypic ratio for the cross c+ c x ch c?
A) 1 normal : 1albino
B) 2 normal : 1 himalayan : 1 chinchilla
C) 1 normal : 2 albino : 1 himalayan
D) 2 normal : 1 chinchilla : 1 albino
E) 2 normal : 1 himalayan : 1 albino
36. What does the F2 genetic ratio 9:7 indicate?
A) complete dominance.
B) codominance.
C) duplicate recessive epistasis.
D) recessive lethal.
E) B and C only
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A) complete dominance.
B) recessive.
C) codominance.
D) all of the above
E) none of the above
37. For snapdragons, the allele W is needed for color expression (w results in no color i.e. white).
The precise color expressed is determined by the alleles R (red) and r (pink). A cross between
certain red and pink plants resulted in progeny as follows:
3/8 red
3/8 pink
1/4 white
What were the genotypes of the plants that were crossed?
A) W/W ; R/R x W/w ; R/r
B) W/w ; r/r x W/W ; R/r
C) W/w ; R/r x W/w; R/r
D) W/w ; R/r x W/w ; r/r
E) w/w ; R/r x W/w ; R/r
A) complementary alleles of two different genes.
B) a heterozygote of the alleles determinine red and white.
C) recessive epistasis.
D) dominant epistasis
E) the presence of a dominant allele at either of two loci (where disc-shape is determined by
the dominant alleles of both loci)
39. Regarding the inheritance of fruit colour in summer squash, the alleles Y and y determine
yellow and green fruit respectively. However, the allele W of a gene on a separate chromosome
is epistatic to the Y and y colour alleles resulting in white fruit (w has no effect on colour). If
plants of genotype Y/y ; W/w are intercrossed, what phenotypic ratio is expected in the progeny?
A) 9 white, 3 green, 4 yellow
B) 1 yellow, 2 white, 1 green
C) 9 yellow, 6 green, 1 white
D) 9 yellow, 4 white, 3 green
E) 12 white, 3 yellow, 1 green
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38. In summer squash, when a plants with disc-shaped fruit are crossed to plants with long fruit,
the F1 all have disc-shaped fruit. However, in the F2 progeny fruit, 9/16 have disc, 1/16 long, and
6/16 are a new shape, sphere. What is the sphere phenotype most likely determined by?
40. Five purebreeding mutant white flowered plants were used in pairwise complementation
tests. The results were as follows: '+' means that the progeny had wild type blue flowers and '–'
means they had white flowers.
A) 1 gene
B) 2 genes
C) 3 genes (1/4/5 and 2 and 3)
D) 4 genes
E) 5 genes
41. The R/r and S/s genes are linked and 10 map units apart. In the cross Rs/rS x rs/rs what
percentage of the progeny will be Rs/rs?
A) 5%
B) 10%
C) 25%
D) 40%
E) 45% (these are the parentals)
42. In Drosophila, singed bristles (sn) and cut wings (ct) are both caused by recessive, X-linked
alleles. The wild type alleles (sn+ and ct+) are responsible for straight bristles and intact wings,
respectively. A female homozygous for sn and ct+ is crossed to a sn+ct male. The F1 flies are
interbred. The F2 males are distributed as follows:
sn ct 13
sn ct+ 36
sn+ ct 39
sn+ ct+ 12
What is the map distance between sn and ct?
A) 12 m.u.
B) 13 m.u.
C) 25 m.u.
D) 50 m.u.
E) 75 m.u.
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How many different genes were the mutations in?
The following information applies to problems 43 & 44. In humans, the genes for red-green color
blindness (R=normal, r=color-blind) and hemophilia A (H=normal, h=hemophilia) are both Xlinked and only 3 map units apart.
43. Suppose a woman has four sons, and two are colorblind but have normal blood clotting and
two have hemophilia but normal color vision. What is the probable genotype of the woman?
A) H R / h r
B) H r / h r
C) h r / h R
D) H r / h R (so that sons are parental combos)
E) H R / H r
A) 0.03
B) 0.15
C) 0.485
D) 0.47
E) 0.015 (1 of the 2 recombinant types)
45. The cross L p q / l P Q x l p q / l p q is carried out, the L gene is found to be in the middle.
What would be the genotypes of the double crossover gametes in this cross?
A) L P Q and l p q
B) L p Q and l P q
C) l p Q and L P q
D) L p q and l P Q
E) cannot be determined
46. In Drosophila, the genes b, c and sp are linked and in the order given, the distances being b-c
= 30 m.u. and c-sp = 20 m.u. These intervals exhibit 90% interference. How many double
crossovers would be recovered in a three-point cross involving b, c and sp out of 1000 progeny?
A) 3
B) 6
C) 54
D) 60
E) 600
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44. A woman whose mother is colorblind and whose father has hemophilia A is pregnant with a
boy and wants to know the probability that he will have normal vision and blood clotting. What is
the probability?
47. In Drosophila, brown eyes (pr) and bright red eyes (cn) are both caused by recessive, Xlinked alleles. The wild-type alleles (pr+ and cn+) combine to give brick red eyes and the double
mutant (pr cn) has orange eyes . A pr cn female is mated to a pn+ cn+ male and the F1 progeny
are interbred. The F2 are distributed as follows:
orange 55
brown
45
bright-red 45
wild type 55
200
What is the value of X2 for a test of the hypothesis that the pr and cn genes are
unlinked?
48. Suppose an individual is heterozygous for two linked pairs of alleles on the same
chromosome arm, A b / a B such that the A locus is closer to the centromere than the B locus.
Under what conditions would a crossover in a somatic cell generate a twin spot, i.e. two adjacent
clones of cells, one clone homozygous for a and the other clone homozygous for b?
A) The crossover would have to occur between the A locus and the centromere and involve
two homologous (non-sister) chromatids.
B) The crossover would have to occur between the A locus and the B locus and involve two
homologous (non-sister) chromatids.
C) The crossover would have to occur between the B locus and the end of the chromosome and
involve two homologous (non-sister) chromatids.
D) A double crossover would have to occur, with one crossover between the A locus and the
centromere and a second crossover between the A and B loci locus and both crossovers would
have to involve two homologous (non-sister) chromatids.
E) No crossover in a somatic cell could generate a twin spot.
49. Which of the following LOD score values is statistically significant?
A) – 3.1
B) 3.1
C) 2.1
D) A and B
E) A and C
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A) 0.5
B) 1.0
C) 2.0
D) 0.4
E) 20
50. Consider a pair of homologous chromosomes heterozygous for three genes (e.g. A B C/a b c)
during prophase I of meiosis. Let the sister chromatids of one homolog be numbered 1 and 2; and
the sister chromatids of the other homolog be numbered 3 and 4. Assume a double crossover
occurs in this pair of chromosomes that results in chromatids of the genotype AbC and aBc. If
the first crossover (the one between A and B) involves chromatids 1 & 4, which chromatids
could be involved in the second crossover?
A) 1 & 2 or 3 & 4
B) 1 & 3 or 2 & 4
C) 1 & 4 or 2 & 3
D) 1 & 3 or 1 & 4 or 2 & 3 or 2 & 4 (this was the given answer but 2&3 does not work)
E) any two of the four chromatids
A) 5'AGTCTAC3'
B) 5'AGCCGCCGCCGCCTAC3'
C) 5'AGCCCAC3'
D) 5'ATCCTAC3'
E) 5'AGCCTGC3'
52. What is the term for a mutation that changes a codon that originally coded for an amino acid
into a stop codon?
A) frameshift mutation
B) missense mutation
C) silent mutation
D) nonsense mutation
E) suppressor mutation
53.What is the heritable disorder fragile X syndrome, a major cause of mental retardation,
caused by?
A) production of enzymes that break the phosphate backbone.
B) UV light.
C) X-rays.
D) presence of an extra X chromosome in the sperm or egg.
E) duplication of multiple three-nucleotide repeats.
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51. Assume that a wild-type sequence is 5'AGCCTAC3'. Indicate the sequence that might be
produced by a transversion.
54. In what way do base analogs differ from other classes of mutagen?
A) they only alter bases.
B) they can only cause transversions.
C) they only work during DNA replication or repair.
D) they can only cause forward mutations, nor reversions.
E) they will not function in bacterial cells.
55. Assume that a new low-calorie sweetener is developed. The structure is novel and is tested
with the Ames test for mutagenicity. The following results are obtained:
What conclusion is most consistent with this data?
A) The sweetener is not mutagenic.
B) Rat liver enzymes are highly mutagenic.
C) The sweetener is not mutagenic but can be converted into strong mutagens (this
is correct but some thought 6 vs 2 was significant too).
D) The sweetener is mutagenic and can be converted into strong mutagens.
E) The sweetener and its conversion products are equally mutagenic.
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Sample
Number of his+ revertent colonies
distilled water
2
distilled water + rat liver enzymes
3
sweetener
6
sweetener + rat liver enzymes
65