Download Name: Date: Title: Problem Solving Techniques. Introduction. The

Name:
Date:
Title: Problem Solving Techniques.
Introduction.
The best way to determine whether you understand the concepts of genetics is to solve problems.
The following information may be helpful to you.
Genetics problems are almost invariably word problems. The first step is to translate the word
problem into genetic terminology, carefully defining any symbols being used. Once this has been
done, solving the problem is usually routine.
Complete knowledge of the mode of inheritance of certain traits requires that you be able to
answer the following questions:
(1)
How many loci are involved?
(2)
How many alleles are there for each locus?
(3)
What are the dominance relationships between the alleles?
(4)
Are any of the alleles recessive lethals?
(5)
If multiple loci are involved, how do they interact?
(6)
If multiple loci are involved, what are their linkage arrangements?
(7)
What is the mode of sex determination in the species?
(8)
Are any of the loci sex linked?
(9)
What are the genotypes of the individuals listed in the problem?
A good first step in problem solving is to determine which of the above points are known. This
will help you to organize the information that you have, and clarify what you need to find out.
Try the following problems. Ask if you need help.
Genetics Laboratory 04.1
(1)
Two black female rats were crossed with a brown male. Several litters were obtained from
each female. The first female produced thirty six black rats; the second produced fourteen
black and ten brown progeny.
What is the likely mode of inheritance of black and brown coat colour in rats?
What are the genotypes of the parents?
(2)
In poultry, rose comb is dominant over single comb. A farmer believes that some of his
rose-combed fowl may carry an allele for single comb.
How could he find out which fowl are heterozygous?
(3)
Huntington's disorder causes progressive irreversible degeneration of the nervous system,
leading to death. Symptoms usually do not appear until middle age. The disease shows
autosomal dominant inheritance.
A man is dying from Huntington's disorder. What are the chances that his fourteen year old
daughter will suffer the same fate, given that three of her grandparents are alive (the fourth
died in a boating accident)?
(4)
A form of peroneal muscular atrophy consists of gradual wasting of the distal muscles of
the limbs, starting between the ages of ten and twenty. Pedigrees show that a person never
has this type of peroneal muscular atrophy unless one of the parents also had it.
What is the likely mode of inheritance of this condition?
(5)
In cattle the heterozygous condition of the alleles for red coat colour (R) and white coat
colour (r) is roan coat colour.
If two roan cattle are mated, what proportion of the progeny will resemble the parents in
coat colour?
(6)
Can the following children be produced from the following parents?
Parent’s Blood Types
A and A
A and B
A and O
A and AB
B and AB
Child’s Blood Type
O
O
AB
O
A
Genetics Laboratory 04.2
(7)
Colour-blindness is a sex-linked trait in humans.
Two people with normal vision have four children.
The first is a daughter who has normal vision. She has three sons, two of whom are colourblind.
The second is a daughter who has normal vision. She has five sons, all of whom have
normal vision.
The third is a son who is colour-blind. He has two daughters and two sons, all of whom
have normal vision.
The fourth is a son who has normal vision. He has four sons, all of whom have normal
vision.
What are the most probable genotypes of all of the individuals described?
(8)
A rooster is heterozygous for a sex-linked recessive lethal allele. What ratio of males to
females will be produced when he is crossed with normal females?
(9)
In guinea pigs, black coat (B) is dominant to albino (b), and rough coat (R) is dominant
over smooth coat (r). The genes B and R are unlinked.
When a cross is made between a homozygous black rough animal and an albino smooth
one, what will be the appearance of the F1 and F2 generations?
What will be the appearance of the offspring of a cross between the F1 generation and an
albino smooth parent?
(10) A black rough guinea pig is crossed with an albino rough one. The progeny consist of
thirteen black rough, sixteen albino rough, six black smooth, and 5 albino smooth.
Identify the genotypes of the parents.
Genetics Laboratory 04.3
(11) In sesame, one-pod is dominant over three-pod, and normal leaf is dominant over wrinkled
leaf. The two characters are inherited independently.
What are the genotypes of the two parents in each of the five experiments listed below?
Parental Phenotypes
a) one-pod normal
x
b) three-pod normal
c) one-pod normal
x
d) three-pod wrinkled
e) one-pod wrinkled
x
f) three-pod normal
g) one-pod normal
x
h) three-pod normal
i) one-pod normal
x
j) one-pod wrinkled
one-pod
normal
Progeny Phenotypes
one-pod
three-pod
wrinkled
normal
three-pod
wrinkled
362
118
0
0
211
0
205
0
78
90
84
88
318
98
323
104
110
113
33
38
(12) In Drosophila, the recessive allele of an autosomal gene (vg) results in vestigial wings. The
recessive allele of an X-linked gene (y) results in a yellow body colour.
If a vestigial-winged, yellow-bodied female is crossed to a homozygous normal male, what
will be the appearance of the F1 and F2 generations?
(13) A plant heterozygous for four independently assorting gene pairs (Aa Bb Cc Dd) is selffertilized.
Determine the expected frequency for each of the following genotypes in the progeny.
a) aa bb cc dd
b) aa bb Cc Dd
c) Aa Bb Cc Dd
Genetics Laboratory 04.4
(14) A locus in mice is concerned with coat pigment production. When parents heterozygous at
this locus are mated, 75% of the progeny are coloured and 25% are albino.
A second unlinked locus controls coat colour. When two yellow mice are mated, 67% of
the progeny are yellow, and 33% are agouti.
Analysis of the progeny of dihybrid crosses indicates that the albino genotype is epistatic to
the agouti locus.
Yellow mice are crossed with albino mice. The progeny are 50% albino, 33% yellow, and
17% agouti. What are the genotypes of the parents?
(15) An allele (ce) of the gene for albinism in mice produces a white coat when homozygous.
The p allele of a gene affecting eye colour produces pink eyes when homozygous.
Mice of the genotype cep+/c+p are testcrossed with mice homozygous for the two mutations.
The progeny obtained are shown below.
Phenotype
dark coat, pink eyes
white coat, dark eyes
dark coat, dark eyes
white coat, pink eyes
Number
274
240
34
31
Calculate the map distance and crossover frequency between the two genes.
(16) Two loci, a and b, are separated by 15 map units.
What is the expected frequency of progeny of normal phenotype from a testcross involving
an a+b /a b+ parent?
(17) In Drosophila, the gene clot (cl) affects eye colour, the recessive allele producing a brown
eye.
Similarly, the recessive allele of the gene safranin (sf) also produces a brown eye colour.
Flies homozygous for the recessive clot allele, but otherwise of normal genotype, are mated
with flies homozygous for the recessive safranin allele, which are also otherwise of normal
genotype. The progeny are testcrossed with a double homozygous recessive strain. The
results are shown below.
Phenotype
brown eyes
wild-type eyes
Number
73
27
Are the two genes linked?
Genetics Laboratory 04.5
(18) The gene clot is mapped with respect to the gene crinkled (ck) in a similar experiment to
that described above.
Phenotype
crinkled
clot
wild-type
clot and crinkled
Number
340
300
183
182
Finally, the gene safranin is also mapped with respect to the gene crinkled.
Phenotype
crinkled
safranin
crinkled and safranin
wild-type
Number
430
400
93
92
Are any of the three genes linked? If so, what is the order of the genes and what are the
map distances between the loci?
(19) Antennapedia (Antp) is a dominant mutation in Drosophila that changes antennae into legs.
rosy (ry) is a recessive eye-colour mutation.
Stubble (Sb) is a dominant mutation that causes short bristles.
Antp ry+Sb+/Antp+ry Sb females are crossed with triply homozygous recessive males, and
the progeny classes below obtained.
Phenotype
Antennapedia
rosy, Stubble
rosy
Antennapedia, Stubble
wild-type
Antennapedia, rosy, Stubble
Stubble
Number
1140
1078
110
70
58
43
2
Determine gene order and map distances.
Genetics Laboratory 04.6
(20) The Drosophila genes ebony (dark body colour), groucho (clumped bristles above eyes),
and rosy (reddish-brown eye colour) are linked.
A student was mapping the three loci. Unfortunately he forgot to record the parental
genotypes. Undaunted, he took the F1 females, which were wild type, and crossed them
with homozygous rosy, groucho, ebony flies.
Phenotype
ebony and rosy
groucho
ebony, groucho, and rosy
ebony
wild-type
groucho and rosy
rosy
ebony and groucho
Number
130
114
61
54
51
43
10
7
What is the genotype of the F1 flies?
Determine the gene order and map distances between the loci.
Genetics Laboratory 04.7