Download 10. In wheat kernel color is determined by a pair of genes in a

MENDELIAN GENETICS HOMEWORK PROBLEMS
1. A rooster with a particular comb shape called walnut was crossed to a hen with a type of comb
called single. The F1 progeny all had walnut combs. When F1 males and females were crossed to
each other, 93 walnut and 11 single combs were found among the progeny, along with 29 chickens
with a new kind of comb called rose and 32 birds with another new type of comb called pea.
a. Explain how comb shape is inherited
b. What progeny would result from crossing a homozygous rose hen with a homozygous pea
rooster? What phenotypes and ratios would be seen in the F2 progeny?
c. A particular walnut rooster is crossed with a pea hen and the progeny consisted of: 12 walnut,
11 pea, 3 rose and 4 single chickens. What are the likely genotypes of the parents?
d. A different walnut rooster was crossed to a rose hen and all of the progeny were walnut. What
are the possible genotypes of the parents?
2. A black mare was crossed to a chestnut stallion and the mating produced a bay son and a bay
daughter. These two offspring were mated to each other several times and they produced
offspring with four coat colors: black, bay, chestnut and liver (sort of grayish brown). Crossing a
liver grandson back to the black mare gave a black foal and crossing a liver granddaughter back to
the chestnut stallion gave a chestnut foal. Explain how coat color is inherited in these horses and
give the possible genotypes for each horse.
3. The following pedigree chart was created from individuals suffering from deafness.
a. Study this pedigree and explain how deafness is being inherited
b. What are the genotypes for the individuals in generation V? Why are they not affected?
4. In a species of tropical fish, a colorful orange and black variety called Montezuma occurs. When
two of these fish are crossed, 2/3 are Montezuma and ¼ are the wild-type dark grayish green
color. Montezuma is a single-trait gene and these fish are never true-breeding.
a. Explain the inheritance pattern and show how your explanation accounts for the phenotype
ratios given
b. In this same species, the shape of the dorsal fin is altered from normal to ruffled by being
homozygous for a recessive allele designated f. What progeny would you expect to obtain and
in what proportions from the cross of a Montezuma fish homozygous for normal fins to a wildtype fish with ruffled fins?
c. What phenotypic ratios of progeny would be expected from crossing two of the Montezuma
progeny you obtained in cross b?
5. In the fruit fly, very dark (ebony) body color is determined by the e allele. The e+ allele produces a
normal, wild-type, honey colored body. In heterozygotes for the two alleles, a dark marking called
a trident can be seen on the thorax of the body but otherwise the body is honey-colored.
a. What kind of inheritance would produce this trident marking?
b. When female e+e flies are crossed to male e+e files, what is the probability that the progeny
will have the trident marking?
c. Flies with the trident markings mate among themselves. Of the 300 progeny, how many would
be expected to have a trident, how many would be ebony and how many honey-colored?
6. Duplication of genes is an important evolutionary mechanism. As a result, many, cases are known
in which a species has two or more identical genes.
a. Suppose there are two genes - A and B - that specify production of the same enzyme. An
abnormal phenotype results only if an individual does not make any of that enzyme. Only one
of these two genes needs to be functional in order to make the enzyme. What ratio of normal to
abnormal progeny would result from a mating between two parents of genotype AaBb where A
and B represent alleles that specify production of the enzyme, while a and b do not?
b. Suppose now there are three genes specifying production of this enzyme and again that a
single functional allele is sufficient for a wild-type phenotype. What ratio of normal vs.
abnormal progeny would result?
7. Familial hypercholesterolemia (FH) is an inherited trait in humans that results in higher than
normal serum cholesterol levels (measured in mg/dl of blood). People with serum cholesterol that
are roughly twice that of normal have a 25 times higher frequency of heart attacks than unaffected
individuals. People with serum cholesterol that are three times or more higher than that of normal
individuals have severely blocked arteries and almost always die before they reach the age of 20.
Four FH pedigree charts from four Japanese families are shown below.
a. What is the most likely mode of inheritance of FH based on these charts? Are there any
individuals in any of these pedigrees who do not fit your hypothesis? What conditions might
account for this?
b. Why do individuals in the same phenotypic class (i.e. unfilled, yellow or red symbols) show
such variation in their levels of serum cholesterol?
8. A woman with type O blood, whose father has type A and whose mother has type B has a child
with type O. There is a dispute over the identity of the child's father. Two men are possible fathers.
One is type AB and the other is type A.
a. What is the mother's genotype?
b. Which man could be the father?
c. If this man is the father, what is his genotype?
d. What are the genotypes of the woman's parents?
9. In the peppered moth, Biston betularia, there are three alleles that determine body color. These
alleles are all at the same locus. The allele for pale color (m) is recessive. A second allele (M’),
which is dominant to m, produces a mottled color called insularia. The third allele (M), which is
dominant to both of the other two, produces a melanic moth (very dark colored). A female moth
having the typical pale color is mated to a male melanic. If half the progeny are melanic and half
are insularia, what were the genotypes of the two parents?
10. In wheat kernel color is determined by a pair of genes in a quantitative way. Each of the two genes
can have two alleles (A1, A2, B1, B2). Kernel color ranges from red, when four type 1 alleles are present, to
white, when four type 2 alleles are present. Three intermediate colors (dark pink, medium pink, and light
pink) can occur depending on the relative numbers type 1 and type 2 alleles. Calculate the expected
proportions of the five phenotypes that would be produced by a cross between two wheat plants with
medium pink kernels that are heterozygous for both genes: A1A2 B1B2 x A1A2 B1B2 .
11. Coat colors of Labrador retrievers depend upon the action of at least two genes. At one locus is the
gene for coat color with the dominant allele resulting in a black color and bb producing a brown color –
known as a chocolate lab. However, at the second locus, a recessive epistatic inhibitor of coat color
pigment (ee) prevents the expression of color alleles at another independently assorting locus, producing
a yellow coat color. When the dominant condition exists at the inhibitor locus (E-), the alleles of the other
locus may be expressed and observed, so the genotype E-B- produces black and E-bb producing
chocolate. Two dihybrid black labs are mated together.
a. determine the phenotypic proportions expected in the progeny
b. determine the chance of choosing, from among the black progeny, a genotype that is
homozygous at both loci.
12. If a heterozygous white (BbWw) mare is crossed with a heterozygous white (BbWw) stallion, what
could the offspring's phenotype and genotype be?
13. Horses can also be bay in color. This dominant gene allele (A) masks the dominant black color, but not
the white gene or the recessive chestnut color. What is the phenotype and genotype of the offspring when
a bay mare (AaBBww) is crossed with a bay stallion (AaBbww)?
14. Horses also carry a dilution gene (D). If only one allele is the dominant D, and a dominant A allele and
the recessive chestnut color genes are present, then the horse will be a palamino. If there are two
dominant dilution alleles (DD) and all else is the same as previously mentioned, the horse will be a
pseudo albino. What is the phenotype and genotype of the offspring when a palomino mare (AAbbDdww)
is crossed with a palomino stallion (AabbDdww)?
15. In clover plants, the pattern on the leaves is determined by a single gene with seven alleles that are
related in a simple dominance series - an allele that determines the absence of a pattern is recessive to
the other six alleles, each of which produces a distinct pattern (i.e. A1  A7). All heterozygous
combinations of alleles show complete dominance
a. How many different kinds of leaf patterns (including the absence of pattern) are possible in a
population of clover plants where all seven alleles are present?
b. What is the largest number of different genotypes that could be associated with any one phenotype? Is
there any phenotype that could be represented by only a single genotype?
c. In a particular field, you find that the large majority of clover plants lack a pattern on their leaves even
though you can identify a few plants representative of all possible pattern types. Explain this finding.
16. In fruit flies, the gene for white eyes is sex-linked recessive. (R) is red and (r) is white. Cross a whiteeyed female with a normal red-eyed male.
a. What percent of the males will have red eyes? White eyes?
b. What percent of the females will have red eyes? White eyes?
c. What total percent of the offspring will be white-eyed?
d. What percent of the offspring will be carriers of the white eye trait?
17. Using the same information as for question #1, cross a heterozygous red-eyed female with a red-eyed
male.
a. What are the genotypes of each parent?
b. What fraction of the children will have red eyes?
c. What fraction of the children will have white eyes?
d. What fraction of the female children will carry the white eyed trait?
18. In humans, hemophilia is a sex-linked recessive trait. If a female who is a carrier for hemophilia
marries a male with normal blood clotting, answer the following questions.
a. What fraction of the female children will have hemophilia?
b. What fraction of the female children will be carriers?
c. What fraction of the male children will have normal blood clotting?
d. What fraction of the male children will be carriers?
e. What fraction of the male children will have hemophilia?
19. Two normal-visioned parents have a color-blind son. Give the genotype of both parents and the son.
20. In cats, the allele (B) produces black color but (b) produces a yellow color. These alleles are
incompletely dominant to each other. A heterozygote produces a tortoise shell color. The alleles (B) and
(b) are sex-linked as well. Cross a tortoise shell female with a yellow male.
a. What percent of their offspring will be yellow?
b. What percent of their offspring will be black?
c. What percent of their offspring will be tortoise shell?
d. Why is it impossible to have a tortoise shell male offspring?
Pedigree Practice Problems: Identify each pedigree as
autosomal recessive, autosomal dominant, X-linked,
or Y-linked. Using the letters A and a, fill in as much of
these charts as you can.