Download Exam1 - Cornell College

Biology 315
10/14/16
Exam 1
1. Genes A, B, and C, are independently assorting and control the production of a black
pigment in plants.
a. Suppose that A, B, and C act in the following pathway:
A
B
C
colorless
black
The alternate alleles that give abnormal functioning of these genes are designated a, b, and c
respectively. A black A/A B/B C/C plant is crossed with a colorless a/a b/b c/c plant to yield
a black F1. The F1 is selfed. What is the probability of producing a colorless plant? Assume
that the products of each step except the last are colorless, so only colorless and black
phenotypes are observed. (5 pts)
b. Suppose instead that a different pathway is utilized. In it, the C allele produces an
inhibitor that prevents the formation of black by destroying the ability of B to carry out its
function. The mechanism is as follows:
A
B
colorless
black
C (inhibitor)
If the F1 (from) above is selfed, what is the probability of producing a colorless plant? (5 pts)
2. A heterozygous female Drosophila carries the recessive mutations a and b in repulsion on the
X chromosome. She is also heterozygous for an X-linked recessive lethal allele,”l”. When
she is mated to a true-breeding, normal male, she yields the following progeny:
Females:
1,000
+++
Males:
405
44
48
2
a++
+b+
+++
ab+
Determine the gene order. (3 pts) b) Calculate the map distance between all three genes. (3
pts) c) Calculate the rate of interference. (3 pts)
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3. The dominant allele “B” codes for black coat color in mice and the recessive allele “b” codes
for brown coat color. The recessive genotype “ee” (for another independently assorting
gene) prevents the expression of “B and b”, making the coat color beige, whereas the
dominant “E_” permits expression of “B and b” (black and brown respectively). Both genes
are autosomal. In the following pedigree, black symbols indicate black coat color, striped
symbols indicate brown coat color and white symbols indicate beige coat color. a) What is
the probability of producing a mouse with a beige coat from a mating of II 4 x III 5? (5 pts)
b) What is the probability of producing a mouse with a brown coat from a mating of III 2 x
III 6? (9 pts). Do all work on this tree.
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4. The father of Mr. Spock, first officer of the starship Enterprise, came from the planet Vulcan;
his mother came from earth. A Vulcan has pointed ears (P), adrenals absent (A), and a rightsided heart (R). All of these alleles are dominant over normal earth alleles. These genes are
autosomal, and they are linked as shown in this linkage map:
P/p
A/a
R/r
15 m.u.
20 m.u.
If Mr. Spock marries an Earth woman and there is no genetic cross-over interference, what
proportion of their children:
a. will have Vulcanian ears and heart but Earth adrenals? (5 pts)
b. will have Vulcanian ears but earth heart and adrenals? (5 pts)
5. The cross “AD x ad is carried out between two strains of Neurospora which produce ordered
octads (note that A and D represent two different genes). An examination of the ascospores
yielded the following data:
classes
1
2
AD
Ad
AD
Ad
AD
Ad
AD
Ad
ad
aD
ad
aD
ad
aD
ad
aD
number: 259
3
3
AD
AD
aD
aD
Ad
Ad
ad
ad
29
4
AD
AD
Ad
Ad
aD
aD
ad
ad
65
5
AD
AD
ad
ad
AD
AD
ad
ad
2
6
Ad
Ad
aD
aD
Ad
Ad
aD
aD
3
7
AD
AD
ad
ad
Ad
Ad
aD
aD
4
8
Ad
Ad
ad
ad
aD
aD
AD
AD
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a) Using diagrams explain why the number of MII asci can be used to determine the map
distance between any gene and the centromere. (3 pts) b) Map all genes. (5 pts) c) Derive
the crossover pattern for class 6. (3 pts)
6. a) Diagram and label what one homologous pair would look like during prophase I and early
anaphase I of meiosis for an individual that is heterozygous for a paracentric inversion with a
crossover within the inverted region. Be sure to indicate (clearly) the inverted region. (5 pts)
b) Assume an individual heterozygous for the paracentric inversion carries the alleles “E” (on
the inverted homologue) and “e” (on the wild-type homologue). Both alleles reside within
the inverted region. Place these alleles on your diagram. This individual is crossed to an
individual homozygous for the paracentric inversion also carrying the alleles “E” and “e” in
the inverted region. List the genotypic ratio of the offspring if a single crossover in the
inverted region occurs in both parents. Assume any gametes that have duplications or
deletions do not produce viable offspring. In order to receive full credit you must briefly
explain your answer. (7 pts)
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7. A strain of Neurospora (ordered) with the genotype A B is crossed to a strain with the
genotype a b. Half the progeny are A B and half the progeny are a b. Using a diagram
representing spore fusion, replication and meiosis I and II, show how this is possible. Briefly
explain your answer. (10 pts)
8. In giant flies mutant genes for purple eye color (p) and no wings (w) are both carried on the
same autosome and separated by 16 map units. These genes are recessive to their counterpart
alleles, p+ and w+, which control wild-type expression of these traits. A third recessive gene
that codes for green body (g) is located on a different autosome. The dominant allele (G)
codes for wild-type body color. Two flies heterozygous for all three loci are crossed. The
female carries the linked genes in coupling phase while the male carries the linked genes in
repulsion phase.
a) What are the genotypes of the parents? (1 pts)
b) What is the probability of producing a giant fly with a recessive phenotype for all
three loci? (4 pts)
c) What is the probability of producing a fly that is heterozygous at all three loci? (7 pts)
9. a) Explain the specific function of the silk worm Masc protein (2 pts)
b) Draw an example of Mendel’s First Law. (2 pts)
c) Describe the specific function of the sme 2 locus in yeast. (2 pts)
d) Provide a specific example of a pleiotropic genetic interaction. (2 pts)
e) How is it possible that mice that inherit two dominant copies of the kit gene, still show the
mutant phenotype? (2 pts)
f) What is the relationship between sry and sox9? (2 pts)
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