Download Answers to test 2

Answers are in green highlight
1. A geneticist crosses two flies as follows: AaBbccDD x aaBbCcDd..
What is the probability of obtaining a fly of genotype aabbCcDD, from this cross
assuming independent assortment of all genes?
a) 3/4
b) 1/2
c) 1/4
d) 1/8
e) 1/16
f) 1/32
g) 1/64
2. For the cross of question 1 above, approximately how many progeny must the
geneticist grow in order to be 99% certain of obtaining the genotype aabbCcDD?
a) 32
b) 94
c) 145 sorry, I managed not to include this on the test paper, so everyone got a mark here
d) 99.9
e) at least 1000
f) cannot be determined
3. For the cross MmNnOoPpQqrr x MmnnOoPPQqRr, assuming that dominance occurs
at each gene and there is independent assortment, how many possible phenotypes would
you expect to occur from this cross?
a) 4
b) 8
c) 12
d) 16
e) 32
f) 48
g) 64
4. For the cross in question 3 above, how many different genotypes would you expect to
obtain from the cross assuming independent assortment?
a) 64
b) 96
c) 144
d) 216
e) 324
f) 486
g) none of the above
1
5. A geneticist conducts a cross to explore two genetic traits in parakeets. One gene
determines tail feather colour with G- giving green tails, and gg giving white tails. The
other gene determines beak shape, with P- giving pointed beak and pp giving round beak.
The geneticist crosses two pure breeding lines (Green tail, round beak x white tail,
pointed beak) and then carries out a test cross. The number of progeny from the test cross
are listed below. Is there any statistical evidence that the two genes are linked?
Green tail
Pointed beak
Observed #
Green tail
White tail
White tail
Round beak Pointed beak Round beak
44
56
55
35
a) There is no statistical evidence for linkage because the chisquare calculated = 6.25
b) There is statistical evidence for linkage because the chisquare calculated = 6.25
c) There is no statistical evidence for linkage because the chisquare calculated = 5.56
d) There is statistical evidence for linkage because the chisquare calculated = 5.56
e) There is no statistical evidence for linkage because the chisquare calculated = 3.84
f) none of the above is correct
6. Use Haldane's mapping function to determine the map distance between two linked
genes, C and D. Two pure lines ccDD x CCdd, are first crossed and a test cross is then
performed. The number of various kinds of progeny are detailed below:
Observed #
CcDd
35
Ccdd
60
ccDd
65
ccdd
40
a) 0.375 cM
b) 37.5 cM
c) 0.693 cM
d) 69. 3 cM
e) 0.625 cM
f) 62.5 cM
g) none of the above
7. Which of the following is NOT correct with respect to a trait determined by polygenic
inheritance?
a) A number of genes, all of equal effect on the phenotype, contribute to it
b) The genes involved are often called polygenes
c) Dominance can occur for genes involved in the trait
d) The environment may also contribute to the trait
e) The minimum number of genes contributing to the trait can be estimated
f) All of the above are correct
2
8. Imagine that a four-stranded double crossover occurs between two linked genes (F and
G) in a double heterozygote with the genotype FG / fg. Which of the following is correct
with respect to the gametes resulting from this single meiosis?
a) gametes are 1 FG, 1 Fg , 1 fG, 1 fg
b) gametes are 2 FG, 2 fg
c) gametes are 2 Fg, 2 fG
d) gametes are 1 FG, 3 fg
e) gametes are 3 FG, 1 fg
f) gametes are 1 fG, 1 Fg, 2 FG
g) cannot be determined without knowledge of the map distance
9) Imagine that the recombination proportion between two linked genes, U and T, is r.
You cross two pure breeding lines of corn, UUTT x uutt to obtain an F1 individual. In
terms of r, what is the expected proportion of UT gametes produced by this F1
individual?
a) r
b) r/2
c) r/4
d) (1-r)
e) (1-r)/4
f) none of the above
10) For the scenario specified in question 9 above, imagine that r = 0.4. You take the F1
individual and self-fertilize it to obtain an F2. What is the expected proportion of UUtt
progeny in the F2?
a) 0.01
b) 0.04
c) 0.09
d) 0.2
e) 0.4
f) none of the above
3
11. Imagine you constructed the map below using a three point test cross. Under the
assumption of no crossover interference, how many double recombinant progeny would
you expect to occur in a sample of 4000 progeny from this testcross?
A
B
5 cM
C
10cM
cM
ccM
a) 0
b) 1.5
c) 7.5
d) 15
e) 20
f) 1000
g) none of the above
12. You cross two strains of Neurospora to study the inheritance of two alleles (D & d) of
the α-dioxygenase gene. The numbers of various kinds of asci obtained are shown below:
D
D
D
D
d
d
d
d
d
d
d
d
D
D
D
D
d
d
D
D
d
d
D
D
d
d
D
D
d
d
D
D
D
D
d
d
D
D
d
d
D
D
d
d
d
d
D
D
242
254
25
24
26
29
Which of the following is correct with respect to these data?
a) the α-dioxygenase gene must be on the mitochondrial genome
b) the α-dioxygenase gene does not show a Mendelian segregation ratio
c) the α-dioxygenase gene is not linked to the centromere
d) the dioxygenase gene is 8.7 cM from the centromere
e) the α-dioxygenase gene is 17.3 cM from the centromere
f) none of the above
13. PKU is caused by a recessive autosomal allele, p. A normal husband and wife both
have fathers with PKU. What is the probability that exactly 2 of their four offspring have
PKU?
a) 0
b) 1/16
c) 9/16
d) 27/128
e) 9/8
f) 27/256
g) none of the above
4
14. You cross two purebreeding parental lines as follows: hhIIJJ x HHiijj , and then
perform a three-point testcross using an F1 individual. The numbers of progeny of
various genotypes are given below. There are 2000 total progeny.
HIJ / hij
20
hij / hij
25
HIj / hij
290
hiJ / hij
300
Hij / hij
580
hIJ / hij
600
HiJ / hij
95
hIj / hij
90
Which one of the following statements is correct?
a) map order is H I J and the distance between H and J is equal to 38.75 cM
b) map order is I J H with the distance between I and H equal to 31.75 cM
c) map order is J H I with the distance between J and I equal to 31.75 cM
d) the expected number of double recombinants is approximately 45
e) there are no double recombinants
f) none of the above
15. You construct an F1 from the cross of two pure breeding lines of plants carrying two
genes that are on the same chromosome but for which at least one crossover always
occurs between these genes (A and B). The initial cross is AABB x aabb. You then self
an F1 plant and grow just two progeny. What is the probability that both progeny show
both dominant traits?
a) 81/256 Since there is always one crossover at minimum, these show indep assort.
b) 9/256
c) 3/4
d) 1/16
e) 1/64
f) this cannot be answered without an estimate of the map distance between the genes
5
16. Below is a pedigree for a common single gene trait in dolphins.
Which of the following is NOT correct with the respect to the possible mechanism(s) of
inheritance of this trait?
a) It could be due to a gene in the mitochondrial genome
b) It could be due to an autosomal dominant
c) It could be due to an X-linked dominant
d) It could be due an X-linked recessive
e) It cannot be due to a Y-linked gene
f) None of the above (they are all correct or possible)
17. Hemophilia A is a genetic disorder caused by a recessive X-linked gene.
A normal male whose father had Hemophilia A, marries a normal woman whose father
also had Hemophilia A. Which of the following is correct with respect to the offspring of
this couple?
a) ¼ of their daughters and ½ of their sons would be expected have Hemophilia A
b) none of the offspring will have Hemophilia A
c) an equal proportion of male and female offspring will have Hemophilia A
d) 1/8 of the sons are expected to have Hemophilia A
e) 3/8 of the females are expect to have Hemophilia A
f) none of the above
6
18. To find a gene for resistance to a fungal pathogen in tomato (indicated as "resist" on
the recombination map), you obtain a recombination map (comprised of SSCP markers
based upon non-coding DNA that you have mapped as well as the resistance gene) and a
corresponding physical map based on the genome sequence. The SSCP markers are
numbered M1, M2, M3 etc. and the distances between them are indicated in
centimorgans. The location of the DNA markers are shown on both the physical and
recombination maps. The physical map also includes the positions of all the genes
indicated as G1, G2, G3 etc which are represented as black boxes. The positions of the
molecular markers are indicated by the short vertical lines.
Recombination map (in cM)
1
2
M1
3
M2
M3
2
M4
3
resist
M5
Physical map
M1
G1 G2
M2
G3
G4
G5 M3
M4 G6
G7
M5
Based upon these maps, which of the following is correct?
a) pathogen resistance is most likely caused by genes G6 and/or G7
b) pathogen resistance is most likely caused by genes G5 and/or G6 and/or G7
c) pathogen resistance is caused by any one of the genes shown on the physical map
d) none of the genes likely cause pathogen resistance
e) M4 or M5 most likely cause the resistance
19. Some plant species exhibit biparental inheritance of chloroplast DNA (called
cpDNA) such that after fertilization the zygote will contain two different cpDNA
genomes. Which of the following is correct for this inheritance mechanism?
a) Mitosis ensures equal segregation of the cpDNA genomes to daughter cells
b) Cytoplasmic segregation of cpDNA genomes will likely occur
c) As the zygote grows into an adult plant, all of its leaves will be variegated
d) All offspring derived from the zygote will possess both cpDNA genomes
e) The inheritance pattern will follow Mendel's laws
20. There are 15 chromosomes in a Telophase I nucleus in a diploid organism. How
many chromatids would you expect to find in a somatic cell before S phase of the cell
cycle?
a) 15
b) 30
c) 45
d) 60
e) none of the above
7
21. The recombination map below provides distances between genes A, B, C etc, in cM.
What is the estimate of the distance between genes C and G?
2
A
15
6
B
C
5
D
4
E
30
F
20
G
H
a) 15 cM
b) 20 cM
c) 28 cM
d) 54 cM
e) 50 cM because the maximum proportion of recombination is 0.5
22. More than two alleles often occur for any particular gene in a population. Imagine
you perform a cross involving 3 alleles of a gene, A1, A2, A3, as follows:
A1A2 x A1A3. Which of the following is correct with respect to this cross?
a) Four different genotypes should occur even though there are 3 alleles
b) All progeny will be heterozygous
c) Two homozygotes are expected, as always in an F2
d) Half of the progeny should carry the A1 allele
e) none of the above
23. A pedigree for a single gene trait in Guinea fowl is shown below. What is the
probability that both of the normal offspring below are heterozygous?
a) 1/9
b) 1/4
c) 1/3
d) 1/2
e) 2/3
f) none of the above
24. For the pedigree in question 23 (above), if the normal female offspring in the
pedigree were to mate with the affected male offspring in the pedigree, what is the
probability that their first offspring will NOT have the trait?
a) 2/3
b) 1/3
c) 1/4
d) 1/8
e) 1/9
f) none of the above
8