GENETICS - BIOL 7 EXAM II -
October 13, 2005 NAME:
DO NOT USE ANY OTHER PAPER AT ANY TIME WITHOUT INSTRUCTOR PERMISSION
Part I: [45 points] Choose the one BEST answer. Circle its
letter. Read each question and all 5 choices carefully because more
than one answer might seem correct at first glance. 1.5
points each
1. In Drosophilla, if a red-eyed female (wild type, + +) is
crossed with a white-eyed male (w), in which generation does it become
clear that w is sex linked?
a. P
b. F1
c. F2
d. not
enough information
e. this
cross can not demonstrate the sex-linkage of w
2. In humans,
a. a man
always passes his X chromosome to his daughters
b. a man
always passes his Y chromosome to his sons
c. a woman
always passes an X chromosome to her sons
d. all of
the above
e. none of
the above are always true
3. The offspring from a testcross with the parental allelic
configuration
a. is
always the largest group of offspring because this is the wild type
b. is half
or more of the offspring because when crossing over occurs, only one
pair of chromatids are involved, so there are always half that remain
parental
c. the
smallest group are the DCO
d. is the
largest group because when crossing over occurs, only one pair of
chromatids are involved, so there are always half that remain parental
e. no
generalization can be made because there is so much variety in biology
4. In moths, the hemigametic sex is ______ ; in Drosophila, the
hemigametic sex is ________
a. male
..... female
b. female
..... male
c.
female ..... female
d. male
..... male
e. there
is none ..... male
5. As the distance between two loci increases, mapping them
becomes
a. more
affected by interference
b. less
accurate
c. easier
to calculate
d. more
accurate
e. a and b
f. c and d
6. Examination of test cross data showed that two linked genes, p
and q, had a recombinant frequency (RF) of 0.091. A third gene, d, had
RFs of 0.173 with p, and 0.256 with q. What is the order of these genes?
a. p-q-d
b. q-p-d
c. q-d-p
d. the genes are not all linked
to each other
e. it is not possible to be sure of
the order from these data
7. Women who are heterozygous for an X-linked condition causing
the absence of sweat glands exhibit patches of skin with sweat glands
and patches lacking sweat glands. This (mosaic) effect is the result of
a.
incomplete dominance
b.
X-chromosome inactivation
c.
complete dominance
d. all
heterozygotes would be expected to display this phenomenon regardless
of sex
e.
co-dominance
8. A trihybrid can produce ___ different gametic genotypes
(with respect to those three genes under study)
a. 2
b. 3
c. 4
d. 8
e. not
enough information given
9. Is the answer to #8 different depending on whether or not the
genes are linked? explain briefly
10. A green female was crossed with a yellow male; a crisscross
inheritance pattern would be
a. all
females are green and all males are yellow
b. all
females are yellow and all males are green
c. all
offsprings are green because green is dominant
d. 50% of
the offsprings are green, 50% are yellow
e. it
depends on whether, in this example, the males or females are
heterogametic
11. In humans, the greater the number of supernumerary X
chromosomes (e.g., XXX or XXY) results in
a. a
higher dosage of femininity
b. the
female being more fertile
c.
increased retardation
d. a and b
e. all of
the above
12. A normal vision woman whose father was colorblind (sex
linked) has children with a normal vision man. The chance of
their having an affected son is
a. 0
b. 25%
c. 50%
d. 75%
e. 100%
13. The chance of the couple described in #12 having an affected
daughter is
a. 0
b. 25%
c. 50%
d. 75%
e. 100%
14. Epistasis is when
a. the
expression of a genotype at one locus depends on the genotype at
another locus
b. an
allele masks the expression of another allele at the same locus
c. the
dosage of an allele effects the expression of another allele
d. a and b
e. all of
the above
15. Wild type alleles are
a. always
dominant
b. always
recessive
c. either
dominant or recessive
d. neither
dominant nor recessive
e. any of
the above might be true; it depends on the gene
16. To determine the distance between three genes, a,b, and c,
a. only
one dihybrid cross is necessary
b. two
different dihybrid crosses are necessary: a - b and b - c
c. three
dihybrid crosses are necessary: a-b, b-c, and a-c
d. each of
these genes must be mapped with respect to a fourth gene, d
e. one
cannot map three genes using dihybrid crosses
17. In X-linked recessive disorders
a. more
males than females show the phenotype under study
b. all of
the offspring of an affected male are affected
c. all of
the sons of an affected male will pass the condition to their offspring
d. if the
recessive allele is rare, almost all the persons showing the phenotype
are female
e. only
females can transmit the allele; only males can express it
18. A test cross is a cross in which
a. one
parent is heterozygous at all loci under consideration
b. both
parents are heterozygous at all loci under consideration
c. one
parent is male; genes under consideration are X-linked
d. one
parent is homozygous recessive (either male or female)
e. either
c or d may be true for a cross to be used as a test cross
19. The distance between loci on a chromosome determines the
probability of
a. mutation
b.
recombination
c.
hemizygosity
d. gene
linkage
e.
heterozygosity
20. Genes A, B, D, E are linked in that order on a
chromosome. A-B is 15cM, B-D is 10cM, D-E is 20cM. The
probability of triple cross over among these four genes is
a. 30%
b. 3%
c. 0.3%
d. 0.03%
e. triple
crossovers are not detected
21. The term "wild type" indicates
a.
organisms found outside captivity
b.
organisms out of control
c.
organisms particularly prone to mutate
d.
organisms which breed true
e. the accepted
"standard" strain of an organism, or allele of a gene (genotype or
phenotype)
22. The purpose of a testcross is to determine the
a.
recombination frequency between or among linked genes
b.
genotype of the tested parent
c.
genotypes of the progeny because any dominant phenotype must be
represent heterozygosity
d. a and b
e. all of
the above
23. Genes r and s are linked autosomal genes whose recombinant
frequency is 5%. Genes g and h are X-linked genes, 10 map units
apart. A homozygous dominant female is crossed with a recessive male;
the F1 females are backcrossed. Which of the following would be
expected for the testcross progeny?
a. nearly
equal frequency of r+sg+h+, r+sgh, rs+g+h+, rs+gh classes
b.
independent segregation of some alleles with respect to some others
c.
different phenotypic ratios in males and females
d. a and b
e. all of
the above
24. For the system in #23 - which of the following would be
expected for the testcross progeny phenotypes?
a. r+s
& rs+together ~ 95% ; r+s+ & rs together ~ 5%
b. r+s
& rs+together ~ 5% ; r+s+ & rs together ~ 95%
c.
approximately equal numbers of r+s+, r+s, rs+, rs
d. either
a or b is true, but we do not know which; both are not true
e. the
answer is different in males and females
f. not
enough information given
25. For the system in #23 - which of the following would be
expected for the testcross progeny phenotypes?
a. g+h
& gh+together ~ 90% ; g+h+ & gh together ~ 10%
b. g+h
& gh+together ~ 10% ; g+h+ & gh together ~ 90%
c.
approximately equal numbers of g+h+, g+h, gh+, gh
d. either
a or b is true, but we do not know which; both are not true
e. the
answer is different in males and females
f. not
enough information given
26. A triply wild-type female mated with a triply recessive
mutant male gives rise to a large number of offspring. All of the
offspring are wildtype. Among the F-2, the males represent many
different phenotypes, but the females are all wildtype. This
indicates
a. the
genes are sex-linked; the mother (P1) was heterozygous at several loci
b. the
genes are sex-linked; the mother (P1) homozygous dominant
c. the
genes are sex-linked but this is a ZZ/ZW organism: the female is
hemizygous
d. the
genes are autosomal
e. not
enough information given
27. If the genes above are linked, which mating would allow
the best mapping?
a. the F-1
b. the
female P-1 with the F-1 male
c. the
female F-1 with the P-1 male
d. one
would have to find another strain altogether - none of these are helpful
e. the
genes are not linked
28. The terms “in repulsion” and “coupled” are used to describe
chromosomes with alleles of genes (under consideration) that are
a. all
dominant versus all recessive
b. all
wild type versus all mutant
c. a mix
of dominant and recessive versus all dominant or all recessive
d. all
mutant versus all wild type
e. a mix
of wild type and mutant versus all wild type or all mutant
29. In Drosophilla, if a white-eyed female (w, w) is crossed with
a red-eyed male (wild type +), in which generation does it
become clear that w is sex linked?
a. P
b. F1
c. F2
d. not
enough information
e. this
cross does not demonstrate the sex-linkage of w
30. If the woman in # 7 had children with a normal (sweaty) male
with no family history of this disorder, the chance that a son would
lack sweat glands is
a. 0
b. 25%
c. 50%
d. 75%
e. 100%
Part II: [56 points] Answer each question completely and
clearly. Show your work for possible partial credit. Make
sure your answer is clearly stated, and easy to find – perhaps put a
box around it. Make sure you have answered all the parts of the
question.
1. 16 points Do the parts of this problem in order –
each answer must make sense given the information you have available up
to that point in the story.
a. An
individual heterozygous at loci A & B was test crossed. The
counted offspring were as follows. What were the parents’
genotypes and phenotypes, including any linkage information, map
distances, etc. that you can determine (give complete
information).
12 AB
36 Ab
34 aB
18 ab
b. An
individual heterozygous at loci B & D was test crossed. The
counted offspring were as follows. What were the parents’
genotypes and phenotypes, including any linkage information, map
distances, etc. that you can determine (give complete
information).
38 DB
8 Db
12 dB
42 db
c. If these genes are all in the same
species, are A & D linked? If so, how far apart are
they? Explain (show your work)
d. If these genes are all in the same species, knowing only what
you know so far:
a. A &
B are coupled, but D is in repulsion to both of them
b. B &
D are coupled, but A is in repulsion to both of them
c. A &
D are coupled, but B is in repulsion to both of them
d. all 3
genes are coupled
e. not
enough information give
f. genes
are not coupled or in repulsion in a species, only in an individual
e. An
individual heterozygous at loci A & D was test crossed. The
counted offspring were as follows. What were the parents’
genotypes and phenotypes, including any linkage information, map
distances, etc. that you can determine (give complete
information).
32 AD
24 Ad
20 aD
24 ad
f. Now it
turns out that the parents in part (a), (b), and (e) are the same (as
each other). Taking all of this information into account,
what were the parents’ genotypes and phenotypes, including any linkage
information, map distances, etc. (give complete information).
g. There
should be some discrepancies in these answers. Explain why they
appear to contradict each other, and how you resolve the discrepancies.
2. Solve the following mapping problems (#2 & 3) 15 points
each. Your final answers should include the genotypes and
phenotypes of both parents, with the genes arranged in the correct
order and in the correct allelic configuration (i.e. dominant and
recessive alleles arranged properly on each chromosome). Map
distances and interference must also be calculated. Please
place the completed answer in one spot so that all of the components
can be easily found.
+ + + 23
+ + d 20
+ b + 435
a + +
2
a + d 445
a b + 40
a b d 32
+ b d
3
3.
♀ ♂
r
q
g
27
r
q
+
1
r
+
g
389
r
+
+
57
+
+
+ 1010
40
+
q
+
452
+
q
g
32
+
+
g
2
4. 10 points Solve the following pedigree. For each
individual, write the genotype [write it next to the symbol in the
pedigree]. Determine the inheritance pattern for the indicated trait
(e.g. recessive, dominant, sex-linked, etc.)
Name the propositus: _______________
Inheritance pattern: _______________
(explain if necessary)
Is this pedigree consistent with sex-linkage? Explain.
What data would confirm that it definitively is, or is not, a
sex-linked gene?
Why might the propositus come to a counselor?
bonus: Write a question that you studied for, and forgetful me, I
neglected to ask. Answer your question. PLEASE ask yourself
something you can answer well! PLEASE answer the question you
actually ask. [up to 5 points awarded based on question &
answer]