Download GENETICS PROBLEMS

GENETICS PROBLEMS
Use another SEPARATE piece of paper to solve these problems. SHOW ALL WORK!
MONOHYBRID & TEST CROSSES
1.
A brown mink crossed with a silverblue mink produced all brown offspring. When these F1 mink were
crossed among themselves they produced forty-seven brown animals and fifteen silverblue animals.
Which expression of color is dominant?
2.
How many of the brown mink in the F2 generation in the preceding problem would you expect to be
homozygous? How many of the silverblue F2 wold likely be homozygous?
3.
How could you determine which of the brown mink in the F2 of problem 2 were homozygous and which
were heterozygous?
4.
In poultry, rose comb is dependent upon a dominant gene R, single comb upon its recessive allele r.
Birds of the Wyandotte breed are required to have a rose comb. In certain strains of Wyandotte,
however, single-combed birds occasionally appear. Why is this?
5.
The Wyandotte breeders never use a single comb bird for mating. When one appears in a flock it is
immediately discarded. Will this practice be sufficient to eliminate the single-comb gene from the
flock?
6.
How can a breeder of Wyandottes eliminate the single-comb gene from his flock most efficiently?
7.
A rose-combed male is mated with two rose-combed females. Female A produces fourteen chicks, all
rose-combed. Female B produces nine chicks, seven of which are rose-combed and two single-combed.
What are the genotypes of the three parent birds?
8.
In sheep, white is due to a dominant gene W, black to its recessive allele w. A white ewe mated to a
white ram produces a black lamb. If they produce another offspring, could it be white? If so, what are
the chances of its being white? List the genotypes of all the animals mentioned in this problem.
9.
In dogs, wire hair is due to a dominant gene, smooth hair to its recessive allele. Two wirehaired dogs
produce a male pup that is wirehaired. To find out most quickly whether he carries the gene for smooth
hair, he should be mated to what kind of female.
10.
In guinea pigs, the allele for rough coat is dominant over the allele for smooth coat. In order for all the
offspring to be smooth-coated, what should the genotype and phenotype of the parents be? Show the
Punnett Square to support your answer.
11.
A black guinea pig crossed with an albino gave 12 black offspring. When the albino was crossed with a
black pig from the F1 generation, 14 black and 5 white were obtained. Is this possible? Why is it not
probable?
12.
Polydactyly is dominant in humans. A six-fingered woman married a man with six toes on each foot.
Before they have children, they would like to be able to predict whether or not their children will have
six digits. How can they figure this out? What do they need to know?
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13.
Danny the dragon breathes fire. Ironically, this is an undesirable recessive trait that the international
consortium of dragons would like to weed out of their populace. They decreed that those dragons who
breathe fire not be allowed to have children. Danny the dragon really wants a kid. What genetic
argument can he give to convince the consortium to allow him to have a child?
14.
Purple fairies are more common than orange fairies. Some orange fairies, in an effort to break down the
lines of segregation and prejudice and to have more orange fairies, decided to break tradition and marry
purple fairies. When the babies are born they are brown. What the heck is going on?
15.
In Drosophila melanogaster the dominant allele for body color yields black flies. If a black male mates
with a gray female, they get all black offspring. One of their offspring mates with a gray fly and
produces 36 black and 38 gray flies. What are the genotypes of all flies involved?
16.
Suppose that you learned that “schmoos” may have long, oval or round bodies and that matings of
schmoos gave the following:
long x oval gave 52 long and 48 oval
long x round gave 99 oval
oval x round gave 51 oval and 50 round
oval x oval gave 24 long, 53 oval and 27 round
What are the genotypes of the three shapes? What genetic principle controls
inheritance of body shape in “schmoos”?
17.
Red and tall Four O’clock carnations were crossed to white short ones. The color trait is explained by
incomplete dominance but the height trait shows that tall is completely dominant. Diagram and explain
the results of this cross.
18.
Suppose that you are an explorer who has found a new species of plant. Some of the plants have red
flowers and some have yellow flowers. You cross a red flowered plant to a yellow flowered one and all
the plants produced have orange flowers. What is the most probable explanation? How would you
prove it?
DIHYBRID CROSSES
19.
In rabbits, the allele for black coat color is dominant over the allele for brown coat color. The allele for
straight hair is dominant over that for curly hair. Someone gives you a male with black straight hair and
a female with brown curly hair. If you bred these two and got a brown curly hair rabbit in the first cross,
how could you explain it?
20.
In peas the allele for axial flowers is dominant over the allele for terminal flowers and the allele for
inflated seedpods is dominant over constricted pods. A cross between two peas with axial flowers and
inflated pods gives the following:
20 with axial flowers, inflated pods
7 with axial flowers, constricted pods
5 with terminal flowers and inflated pods
2 with terminal flowers and constricted pods
What is the most probable genotype for the two parents? Show a Punnett square to support your answer.
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21.
In rabbits, spotted coat (S) is dominant over solid color (s), and black (B) is dominant to brown (b). A
brown spotted rabbit is mated to a solid black one and all their offspring are black spotted. What are the
genotypes of the parents? If two of the F1 rabbits were mated, what would the appearance of the F2 be?
22.
The long hair of Persian cats is recessive to the short hair of Siamese, but the black coat color of
Persians is dominant to the black & tan coat of Siamese. If a pure black, longhaired Persian is mated to
a pure shorthaired black & tan Siamese, what will be the expected appearance of the F1? If two of these
F1 cats are mated, what is the chance of obtaining a longhaired, black and tan cat in the F2?
23.
The litter resulting from the mating of two short-tailed cats contains three kittens without tails, two with
long tails, and six with short tails. What would be the simplest way of explaining the inheritance of tail
length in these cats? Show genotypes.
24.
In peas an allele for tall plant (T) is dominant over the allele for short plants (t). An allele of another
independent gene produces smooth peas (S) and is dominant over the allele for wrinkled peas (s).
Calculate the phenotypic and genotypic ratios for the results of each of the following crosses:
a. TtSs x TtSs
b. Ttss x ttss
c. ttSs x Ttss
d. TTss x ttSS
SEX LINKAGE
25.
One pair of genes for coat color in cats is sex-linked. The gene (B) produces yellow coat, (b) produces
black coat, and (Bb) produces tortoise-shell color. What kind of offspring would result from the mating
of a black male and a tortoise-shell female?
MULTIPLE ALLELES
26.
Three babies are mixed up in the hospital. The blood groups and parents are as follows:
Mr. Zen
Mrs. Zen
O
AB
Baby 1
AB
Mr. Dee
Mrs. Dee
BO
O
Baby 2
A
Mr. Soo
Mrs. Soo
AB
AA
Baby 3
O
Match the parents with their correct children.
27.
Suppose a father of group A and a mother of group B have a child of group O. What groups are possible
in their later children and in what ratios?
28.
If a man with blood type B, one of whose parents had blood type O, marries a woman with blood type
AB, what will be the theoretical percentage of their children with blood type B?
29.
Both Mrs. Smith and Mrs. Jones had babies the same day in the same hospital. Mrs. Smith took home a
baby girl, whom she named Shirley. Mrs. Jones took home a baby girl whom she named Jane. Mrs.
Jones began to suspect, however, that her child had been accidentally switched with the Smith baby in
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the nursery. Blood tests were made: Mr. Smith was type A, Mrs. Smith type B, Mr. Jones type A, Mrs.
Jones type A, Shirley type O, and Jane type B. Had a mix-up occurred?
CROSSING OVER
30.
In Drosophila melanogaster there is a dominant allele for gray body color and a dominant allele of
another gene for normal wings. The recessive alleles of these two genes result in black body color and
vestigial wings respectively. Flies homozygous for gray body and normal wings were crossed with flies
that had black bodies and vestigial wings. The F1 progeny were then test-crossed, with the following
results:
Gray body, normal wings
Black body, vestigial wings
Gray body, vestigial wings
Black body, normal wings
236
253
50
61
Would you say that these two genes are linked? If so, how many units apart are they on the
chromosome?
31.
In rabbits the dominant allele of a gene produces spotted body color, and the recessive allele solid body
color. The dominant allele of another gene produces short hair, and the recessive allele long hair.
Rabbits heterozygous for both characteristics were mated with homozygous recessive rabbits. The
results of this cross were as follows:
Spotted, short hair
Solid, short hair
Spotted, long hair
Solid, long hair
96
14
10
80
What evidence for linkage is shown in this cross? Give the percentage of recombination and the map
distance between the genes.
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