11 February 2014
Chapter 3
Practice problems
3.1 Herzog et al. (1992) have described a polymorphism in chromosome-3 of the black-handed
spider monkey. The centromere is in the middle of the chromosome in one type (type A) of
chromosome-3, while in the other type (type B) the centromere is near the end of the
chromosome; both chromosomal types are of equal total length. There are no observable
differences in any of the other chromosomes.
(a) What type of chromosomal rearrangement is likely to be responsible for this polymorphism?
Be as specific as possible.
(b) Assume that a zoo that is interested in developing a captive breeding program for this species
contacts you as a consulting geneticist. Would you recommend that individuals brought into
captivity be screened for this chromosomal polymorphism? If so, how should this information
be used in the breeding program? Write a letter to the director of the zoo that explains and
justifies your answer. Make sure that you address the potential effect of this rearrangement both
in the captive population and in the wild following reintroduction.
3.2 As described Section 3.1.7, there is controversy in the literature over whether or not Bornean
and Sumatran orangutans should be considered separate species. What practical effect does the
resolution of this issue have from a conservation perspective? That is, how could affect
conservation efforts with orangs?
3.3 – 3.7. The diagrams below show hypothetical results of protein electrophoresis of a sample
of 20 individuals from a population of sea otters. Note samples from each individual were
electrophoresed and stained for three different enzymes that are each encoded by a single locus
(A, B, and C). This population is diploid and mates at random with respect to these loci.
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3.3 Designate the most common allele at each locus 1, the second most common allele 2, and so
on. Write down the genotype (e.g., 11, 12, etc.) of each individual in the table below. For
example, the first individual is homozygous (11) for the common allele at locus A; the second
individual is heterozygous (12) at A, and individual 16 is homozygous (22) for the rare allele at
this locus.
Indiv. Locus A Locus B Locus C
1
11
2
12
3
4
5
6
7
8
9
10
2
11
12
13
14
15
16
22
17
18
19
20
3.4 What proportion of the three loci in this sample that is polymorphic?
3.5 What is the observed heterozygosity for each locus?
3.6 What is the average observed heterozygosity over all three loci?
3.7 What are the expected genotypic distributions for locus A in progeny from a mating between
individuals 1 and 2?
3.8 What are the expected genotypic distributions for locus C in progeny from a mating between
individuals 1 and 16? How about between individuals 11 and 13?
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3.9 Ling-Ling was a female giant panda at the National Zoo in Washington, D.C. (O’Brien et al.
1984). In March of 1983, Ling-Ling copulated with her male companion Hsing-Hsing. LingLing also was artificially inseminated with sperm from a male giant panda at the London Zoo,
Chia-Chia. On 21 July 1983 she gave birth to a baby that died shortly after birth. The following
genotypes were detected at six protein loci by protein electrophoresis. Which male was the
father of Ling-Ling's baby?
Locus
Ling Ling
Baby
Hsing Hsing Chia Chia
1
AA
Aa
Aa
AA
2
Bb
bb
bb
bb
3
Cc
Cc
cc
cc
4
dd
Dd
Dd
dd
5
Ee
Ee
EE
Ee
6
FF
FF
FF
Ff
3.10 Black and Johnson (1979) reported an highly unusual pattern of inheritance of allozyme
polymorphisms in the intertidal anemone Actina tenebrosa from Rottnest Island in Western
Australia. This species is viviparous, and up to 5 young are brooded by adults at a time until
they are released as relatively large juveniles. The following parental and progeny genotypes
were found at three allozyme loci:
Parental
No. of
Progeny genotypes
Locus genotype broods
FF
FS
SS
MDH
PGM
SOD
FF
25
68
0
0
FS
53
0
158
0
SS
11
0
0
35
FF
44
145
0
0
FS
9
0
33
0
FF
71
225
0
0
FS
18
0
50
0
SS
1
0
0
2
How would you explain these results? That is, what system of mating and reproduction would
explain the observed parent-progeny combinations?
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Assignment Problems
3.11 Molecular genetic markers have allowed us to study reproductive behavior in wild
populations than were not possible previously. For example, evidence of extra-pair copulations
is accumulating in many bird species. Price et al. (1989) used a single allozyme locus (lactate
dehydrogenase, LDH) to study parentage in house wrens. The authors were interested in
detecting both extra-pair copulations (when the female mates with a male other that her “mate”)
and egg dumping (when a female lays an egg in the nest of another female).
They presented the following data:
Parental genotypes
(female x male)
Number
of pairs
Chicks
FF
FS
SS
SS x SS
6
0
4
29
SS x FS
6
0
13
18
FS x SS
4
0
10
11
FF x SS
2
0
8
2
Do these data provide evidence for either extra-pair copulations or egg dumping in this
population?
3.12 The Eastern Reef Egret in Australia usually has solid gray plumage. There is also a white
morph that is fairly common in some populations. Assume that the white phenotype is due to a
recessive allele (g) and that the dominant allele (G) produces gray plumage.
(a) What are the expected phenotypic ratios for male and female progeny from a cross between a
white female and a gray male that had a white mother? Assume that this locus is on an
autosome.
(b) Assume instead that the G locus occurs on the Z-chromosome. How would this affect the
expected phenotypic ratios for male and female progeny from a cross between a white female
and a gray male that had a white mother?
Remember that in birds males are ZZ, and females are ZW. In addition, the W chromosome
does not contain functional gene copies for many of the genes that are found on the Z. Therefore
–
Males: GG = gray
Gg = gray
gg = white
females: GW = gray
gW = white
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3.13 – 3.17 The diagrams below show hypothetical results of protein electrophoresis of a sample
of 20 individuals from a population of sea otters. Note samples from each individual were
electrophoresed and stained for three different enzymes that are each encoded by a single locus
(A, B, and C). This population is diploid and mates at random with respect to these loci.
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3.13 Designate the most common allele at each locus 1, the second most common allele 2, and so
on. Write down the genotype (e.g., 11, 12, etc.) of each individual in the table below. For
example, the first individual is homozygous (11) for the common allele at locus A; the second
individual is heterozygous (12) at A, and individual 16 is homozygous (22) for the rare allele at
this locus.
Indiv. Locus A Locus B Locus C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
3.14 What proportion of the three loci in this sample is polymorphic?
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3.15 What is the observed heterozygosity for each locus?
3.16 What is the average observed heterozygosity over all three loci?
3.17 What are the expected genotypic distributions for locus B in progeny from a mating
between individuals 9 and10?
3.18 What are the expected genotypic distributions for locus C in progeny from a mating
between individuals 1 and 16? How about between individuals 11 and 13?
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