Mendelian Genetics
Workbook
Name ____________________________________________
1. Basic Monohybrid Practice Problems
1. A pea plant with round seeds is cross-pollinated with a pea plant that has wrinkled
seeds. For the cross indicate the following:
a. the genotypes of the parents if the round-seed plant were heterozygous
b. the gametes produced by the round and wrinkled-seed parents
c. the genotypes and phenotypes of the F1 generation
d. the F2 generation if the two rounded plants from the F1 generation were
allowed to cross-pollinate
2. For Labrador retrievers, black fur color (B) is dominant to yellow (b).
a. If a homozygous black male mated with a homozygous yellow female, what
would the puppies look like?
b. Explain how a homozygous black dog can have a different genotype than a
heterozygous black dog.
c. Could the heterozygous black dog have the same genotype as a yellow-haired
dog? Explain.
3. For Dalmation dogs, the spotted condition is dominant to non- spotted.
a. Using a Punnett square, show the cross between two heterozygous parents.
b. A spotted female Dalmation dog mates with an unknown father. From the
appearance of the pups, the owner concludes that the male was a Dalmation.
The owner notes that the female had six pups, 3 spotted and three non-spotted.
What is the phenotype of the unknown male?
4. For Mexican hairless dogs, the hairless condition is dominant to hairy. A litter of
eight pups is found; six are hairless and two are hairy. What is the genotype of their
parents?
2. Monohybrid Crosses
1.
Circle the heterozygous genotypes.
AA ss
2.
Bb
Ss
rr
ii
Ii
RR Tt
Given that white coats (W) are dominant to black (w) in sheep, what are the
phenotypes of the following genotypes?
Homozygous dominant _____ Heterozygous _____ Homozygous Recessive _____
3.
In pigs white color (W) is dominant and black (w) is recessive. Using diagrams and
mathematics, show the results of the following crosses.
a.
a pure white pig is mated with a pure black pig
b.
two heterozygous pigs are mated
c.
a heterozygous pig is mated with a pure white pig
4.
5.
A female hog may give birth to as many as 16 offspring in a single litter. If white
color is dominant over black, give the genotypes and phenotypes of the parents for
each of the following litters.
a.
16 black piglets
b.
8 black piglets and 8 white piglets
c.
16 white piglets
In the following cases, Z stands for a certain dominant gene and z stands for a certain
recessive gene. What ratios of genotypes would you expect from the following
crosses?
a.
ZZ x zz
b.
Zz x Zz
c.
Zz x zz
d.
Zz x ZZ
6.
7.
A spotted rabbit, when crossed with a solid-colored rabbit, produced all spotted
offspring. When these F1 rabbits were crossed among themselves, they produced 32
spotted rabbits and 10 solid-colored rabbits.
a.
Which of the characters is governed by a dominant gene?
b.
How many of the spotted rabbits in the F2 generation would be expected to be
homozygous?
c.
How many of the solid-colored rabbits in the F2 generation would be
homozygous?
As Mendel discovered, yellow seed color in peas is dominant to green. In the
following experiments, parents with known phenotypes but unknown genotypes
produced the listed progeny. Using the letter Y for the yellow gene and y for the
green gene, give the most probable genotype for each parent
Parents
yellow x green
Yellow
82
Green
78
yellow x yellow
118
39
green x green
0
50
yellow x green
74
0
yellow x yellow
90
0
Parental Genotype
8.
In fowl, silky feathers are recessive to normal feathers.
a.
If we have 100 birds raised from a cross between individual heterozygous for
the gene, how many would be expected to be silky and how many would be
expected to be normal?
b.
If we had a normal feather bird, what would be the easiest way to determine of
it was homozygous or heterozygous?
3. Multiple Alleles
1.
Multiple alleles control the coat color or rabbits. A gray color is produced by a
dominant allele C. The Cch allele produces a silver-gray color when present in the
homozygous condition, CchCch, called chinchilla. When Cch is present with a
recessive gene, a light silver-gray color is produced. The allele Ch is recessive to both
the full-colored allele and the chinchilla allele. The Ch allele produces a white color
with black extremities. This coloration pattern is called Himalayan. An allele Ca is
recessive to all genes. The Ca allele results in a lack of pigment, called albino. The
dominance hierarchy is C > Cch> Ch > Ca. The table below provides the possible
genotypes and phenotypes for coat color in rabbits. Notice that four genotypes are
possible for full-color but only one for albino.
Phenotypes
full color
chinchilla
light gray
himalaya
albino
Genotypes
CC, CCch, CCh, CCa
CchCch
CchCh, CchCa
ChCh, ChCa
CaCa
a.
Indicate the genotypes and phenotypes of the F1 generation from the mating of
a heterozygous Himalayan-coat rabbit with an albino-coat rabbit.
b.
The mating of a full-color rabbit with a light-gray rabbit produces two fullcolored offspring, one light-gray offspring, and one albino offspring. Indicate
the genotypes of the parents.
c.
A chinchilla-color rabbit is mated with a light-gray rabbit. The breeders know
that the light-gray rabbit had an albino mother. Indicate the genotypes and
phenotypes of the F1 generation from this mating.
2.
3.
If a silk worm having a white body is crossed with a worm having a pink body, the F1
worms are all peach-colored bodies. From this evidence alone, what phenotypes and
ratios would you expect to find if these crosses:
a.
white crossed with white
b.
white crossed with peach
c.
pink crossed with pink
d.
pink crossed with peach
Yellow guinea pigs crossed with white ones always produce cream colored offspring.
a. Diagram this cross and give genotypes and phenotypes
b.
Two cream colored guinea pigs when crossed produce offspring in the F2
generation. Give the ratios of the F2 genotypes and phenotype
c.
Explain the inheritance pattern of color in guinea pigs.
4.
In short horn cattle, red coat color is incompletely dominant over white, to give roan.
A breeder of short horn cattle has cows which are white and a bull which is roan.
What proportion of the calves produced will be white? roan? red?
5.
Starting with a roan bull and white cows, how could you eventually establish a true
breeding red herd? white herd?
6.
When chickens with splashed white feathers are crossed with black feathered birds,
their offspring are all slate blue. When slate blue are crossed among themselves, they
produce splashed white, slate blue and black in the ratio of 1:2:1 respectively.
7.
a.
How are these feather traits inherited?
b.
Using any appropriate symbols, indicate the genotypes for each phenotype.
In mink, homozygous brown coat is incompletely dominant over silver giving silver
blue.
a.
If two heterozygous mink are crossed what fraction of the offspring will be
brown? silver? silver blue?
b. If there were 12 offspring, how many of each phenotype would be expected?
4. Blood Typing
1.
Indicate the blood types possible for the mating of a male who is blood type O with a
female of a blood type AB.
2. a. Could a male with blood type AB ever have a child with blood type AB? Explain.
b. Could a male with blood type AB ever have a child with blood type O? Explain.
3.
Could a man with type O blood have a child that was type B?
4.
Four babies were born in a hospital on a night in which an electrical blackout
occurred. In the confusion that followed, their identification bracelets were switched.
Conveniently, the babies are of four different blood groups O, A, B and AB. The four
pairs of parents have the following blood groups: O and O, AB and O, A and B, and
B and B. Which baby belongs to which parents?
5.
Suppose a father of type A blood and a mother of type B blood have a child of type O
blood. What blood groups are possible in their subsequent children?
6.
A father with type B blood and a mother with type O blood have a child with type O
blood. What are the chances that their next child will be type O? type B?
7.
Suppose a father and mother claim they have been given the wrong baby at the
hospital. Both parents are type A, but the baby they have been given is type O. What
conclusions could be made in such a situation? If the baby had been type B what
conclusions could be made?
5. Dihybrid Crosses
1.
2.
What kinds of gametes would be produced by organisms having the following
genotypes?
a.
AaBB
b.
aaBB
c.
AABB
d.
AaBb
e.
Aabb
f.
AaBBCc
What would be the genotypes of the offspring in the following crosses?
a. AaBb x AABB
c.
AABB x aabb
b. AaBb x AaBb
d. AaBb x aabb
3.
In garden peas, axial flower position is dominant and terminal flower position is
recessive. Tall plants are dominant to short plants. A plant that is known to be
purebred for tall vine and axial flowers is crossed with a plant having short vines
bearing terminal flower. What is the phenotype of the offspring? Predict the kinds of
offspring that would appear in the F2 generation , using genotypic and phenotypic
ratios.
4.
In horses black color is dominant to chestnut and pacer is dominant to trotter. If a
homozygous black trotter is mated to a homozygous chestnut pacer, what is the
phenotype and genotype of the offspring? Of an F2 generation?
5.
Some dogs bark while others are silent when trailing. The barking characteristic is
due to a dominant gene. Erect ears are dominant to drooping ears. What kind of pups
would be expected from a mating between a heterozygous erect-eared barker and a
drooped-eared silent trailer?
6.
7.
In cattle the polled condition (hornless) is dominant over the horned, and the
heterozygous condition of red coat and white coat is roan. If a homozygous polled
white animal is bred to a horned red one, what will be the appearance of the F1? Of
the F2?
In snapdragons red flower color (CR) and white flower (CW) cause an intermediate
inheritance of pink when heterozygous. Normal (broad) leaves (LB) are nondominant to narrow (grasslike) leaves (LN), the heterozygotes having leaves of
medium breadth. If a red-flowered, broad-leaved plant is crossed with a whiteflowered, narrow leaved one, what will be the phenotypes and their expected ratios in
the F2 generation?
6. Sex-Linkage
1.
One form of hemophilia in man is due to a recessive sex-linked gene. A man whose
father was hemophilic but has normal blood clotting himself marries a woman with
no record of hemophilia in her ancestry. What is the chance of hemophilia occurring
in their children?
2.
A woman whose father was hemophilic but is not a bleeder herself marries a normal
man. What is the chance of hemophilia in their children?
3.
In cats there is a gene for coat color which is codominant and sex-linked. There is
one gene for yellow and one for black, but the heterozygote has a peculiar mixture of
yellow and black which is called tortoise-shell.
a.
What type of kittens would be produced from a cross between a black female
and a yellow male?
b.
What kind of offspring would be expected from a cross of a black male and a
tortoise-shell female? What are the chances of getting a tortoise-shell female
from this cross?
4.
An albino, non-hemophilic man marries a normally-pigmented, non-hemophilic
woman whose father was hemophilic and whose mother was an albino. What kind of
children could they have and in what ratio?
5.
Baldness is a sex-linked trait. A non-bald man marries a non-bald woman. They
have a son and a daughter. At the age of 35 the son becomes bald. What are the
chances that the daughter will also become bald?
6.
The male lion has a well-developed mane which the female does not have. How
could you account for this on a genetic basis?
7.
8.
A husband and wife have normal vision, although both of their fathers were color
blind, which is inherited as a sex-linked recessive condition. What is the probability
that their first child will be:
a.
a normal son?
b.
a normal daughter?
c.
a color-blind son?
d.
a color blind daughter?
In Drosophila, a sex-linked recessive mutation, scalloped (s), causes irregular wing
margins. Diagram the F1 and F2 results if:
a.
b.
a scalloped female is crossed with a normal male
a scalloped male is crossed with a normal female
7.
1.
2.
Pedigree Problems
In humans, the allele for normal hearing (H) is dominant over the recessive allele for
congenital (inherited) deafness (h). Use the figure to answer the following questions:
a.
How is it possible for the individual II - 5 to be congenitally deaf if neither
parent has the condition?
b.
What is the probability that the female, III - 1 will be congenitally deaf?
Assume that the person II - 1 is not a carrier of the trait.
For some people, the chemical PTC has a very definite taste. But others cannot taste
the chemical at all. Use the accompanying pedigree chart to try to determine which
trait is dominant. The shaded areas represent the offspring who can taste the chemical.
As well, determine as far as possible the genotype of the individual on the chart who
can taste PTC.
3. For the pedigree shown below, which depicts the inheritance pattern of a recessive
sex-linked trait in humans (a), determine all genotypes that can be predicted with
absolute assurance.
4.
For the following pedigree, predict the mode of inheritance and the resulting genotype
of each individual. Assume that the alleles “A” and “a” control the expression of the
trait.
5. The following pedigree is for myopia in humans. Predict if the disorder is inherited as
the result of a dominant or recessive allele. Determine the most probable genotype for
each individual based on your prediction.
6.
Analyze the following pedigree. What is the most likely mode of inheritance? Defend
your answer by stating what information supports your answer and what information
rules out other potential modes.