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APGENETICS1206.WKT
PRACTICE GENETICS PROBLEMS
Directions: If a Punnett Square is required, clearly show your work on a
a separate piece of paper. Use pencil and be neat. Illegible work will not be
graded. Do the problems in numerical order and number your answers down (not
across) the page. This page should be stapled to the front of your work.
2015-2016: Do problems 2, 4, 7, 11, 12, 13, 16, 18, 21, 27, 29, 30, 32, 33.
1) In peas, axial flowers are dominant over terminal flowers. What phenotypic ratios would
you expect in offspring from a cross between a known heterozygous axial-flowered plant
and one whose flowers are terminal?
2) The light color variation in the peppered moth is inherited as a simple recessive
characteristic. If a light moth is crossed with a dark moth which had a light parent, what
percent of their offspring will be light?
3) The dominant gene W produces wire-haired texture in dogs; its recessive allele w
produces smooth hair. A group of heterozygous wirehaired dogs are crossed and all of
their wirehaired progeny are then test-crossed. What is the expected phenotypic ratio
among the test-cross progeny?
4) In pigeons, the grizzle color pattern depends on a dominant autosomal gene G. A
mating of two grizzle birds produced one nongrizzle youngster this year. If this pair of
pigeons produces more youngsters next year, what percent would be expected to be
grizzles?
5) Among white human beings, when individuals with straight hair mate with those with
curly hair, wavy-haired children are produced. If two individuals with wavy hair mate,
what phenotypes and ratios would you predict among their offspring?
6) In cocker spaniels, black color is due to a dominant gene B and red color to its recessive
allele b. Solid color is dependent on a dominant gene S and white spotting on its
recessive allele s. A solid red male was mated to a black and white female. They had
five puppies: one black, one red, one black and white, and two red and white. What
were the genotypes of the parents?
7) Suppose a male red cocker spaniel whose mother was spotted red was mated with a
solid black female whose mother was also spotted red. What phenotypes and in what
proportions might be expected from such a cross?
8) Ignoring modifier genes, we can think of brown eyes in human beings as determined by
a dominant allele B and blue eyes by a recessive allele b; free earlobes are determined
by a dominant allele F and attached earlobes by a recessive allele f. A brown-eyed man
with attached earlobes (whose mother was blue-eyed) marries a blue-eyed woman with
free earlobes (whose father had attached earlobes). What phenotypes may be expected
among their children?
9) The allele for pea comb (P) in chickens is dominant to that for single comb (p), but the
alleles black (B) and white (B’) for feather color show partial dominance, B/B’ individuals
having “blue” feathers. If birds heterozygous for both alleles are mated, what proportion
of the offspring is expected to white-feathered and pea-combed?
10) In a P cross, an A/A B/B C/C individual is paired with an a/a b/b c/c individual. Assuming
no linkage, what will be the expected frequency of A/A b/b C/c individuals in the F2
generation?
11) A genetic disease known as Marfan Syndrome is caused by a dominant allele. In this
disease the fingers and toes are excessively long. This and other skeletal defects are
often accompanied by a misplaced eye lens and defects of the heart. Some individuals
with this syndrome may have all the defects; others show only one or two of the defects
yet may have children with all of them. Suppose a normal woman marries an affected
man whose mother was normal. If this trait has 90 percent penetrance, what
percentage of their children will be expected to express the trait?
a. 22.5 percent
b. 45 percent c. 50 percent d. 67.5 percent e. 90 percent
12) The rare trait ocular albinism is inherited as sex-linked recessive. A man with ocular
albinism marries a woman who neither has the condition nor is a carrier. Which one of
the following is the best prediction concerning their offspring?
a. All of their sons will have ocular albinism
b. All of their children of both sexes will have ocular albinism.
c. About 50 percent of their sons will have ocular albinism, and all their daughters
will be carriers.
d. About 50 percent of their daughters will have ocular albinism, but all their sons
will have normal eyes.
e. None of their children will have ocular albinism, but all their daughters will be
carriers.
13) Look at
a.
b.
c.
d.
the pedigree above. This type of deafness is probably inherited as:
autosomal dominant
autosomal recessive
a sex-linked recessive trait
a sex-linked dominant trait
14) The male in the first generation on the top right is probably:
a. D/D
b. D/d
c. d/d
d. XD/Y
e. Xd/Y
15) A certain man has the genotype AB/ab; genes A and B are one chromosome and a and b
are on the homologous chromosome. Suppose crossing over occurs during a meiotic
division in this man’s testis. With regard to the two genes discussed here, how many
genetically different types of sperm cells will be result?
a. 1
b. 2
c. 4
d. 8
e. 16
16) Consider two linked autosomal genes. The dominant allele C of the first gene causes
cataracts of the eye, whereas its recessive allele c produces normal eyes. The dominant
allele of the second gene P causes polydactyly (presence of an extra finger on each
hand), whereas its recessive allele p produces normal hands. A man with cataracts and
normal hands marries a woman with an allele for polydactyly and normal eyes. Their son
has both cataracts and polydactyly. The son marries a woman with neither trait.
Assuming no crossing over, what is the probability that their first child will have both
cataracts and polydactyly?
17) Cystic fibrosis in inherited as a simple recessive allele. Suppose a woman who carries the
trait marries a man who has no alleles. What percent of their children would be
expected to have the disease?
18) Knowledge of the bloodtype genotypes of a certain couple leads us to say that if they were
to have many children, the ratios of the children’s blood types would be expected to be
approximately ½ type A and ½ type B. It follows that the blood types of the couple are:
a. A and B
b. AB and B
c. AB and B
d. AB and A
e. AB and O
19) In an emergency, An unconscious person could receive blood safely from a person with
blood type:
a. A negative b. A positive
c. B
d. O positive
e. O negative
20) Singer Arlo Guthrie has a 50 percent chance of dying prematurely from the same genetic
disease that killed his father, Woody Guthrie. (Woody Guthrie wrote the song, “This
Land is Your Land”). Neither Woody’s Guthrie’s mother nor Arlo Guthrie’s mother carries
any allele for this disease, Huntington Disease. What type of inheritance pattern does
this disease have?
a. autosomal dominant
b. sex-linked dominant
c. autosomal recessive
d. sex-linked recessive
21) An adopted child (blood type O) has located her biological father and discovered that he
had blood type B. Which blood type does she know her biological mother does not have?
22) A particular sex-linked recessive disease of humans isn’t usually fatal. Suppose then, by
chance, a male with the disease lives past puberty and marries a woman heterozygous
for the trait. If they have a daughter, what is the probability that she will have the
disease?
23) In squash an allele for white color (W) is dominant over the allele for yellow color (w).
Give the genotypic and phenotypic ratios for the results of each of the following crosses:
a. W/W x w/w
b. W/w x w/w
c. W/w x W/w
24) If a brown-eyed man marries a blue-eyed woman and they have 10 children, all browneyed, can you be certain that the man is homozygous? If the 11th child has blue eyes,
what will that show about the father’s genotype?
25) The litter resulting of 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 the genotypes.
26) When Mexican hairless dogs are crossed with normal-haired dogs, about half the pups
are hairless and half have hair. When, however, two Mexican hairless dogs are mated,
about a third of the pups have hair, about two-thirds are hairless, and some deformed
puppies are born dead. Explain these results.
27) In peas, an allele for tall plants (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 both phenotypic ratios and genotypic ratios for the
results of each of the following crosses:
a. T/t S/s
b. T/t s/s
c. t/t S/s
d. T/T s/s
x
x
x
x
T/t S/s
t/t s/s
T/t s/s
t/t S/S
28) In Leghorn chickens, colored feathers are produced by a dominant allele, C; white feathers are
produced by the recessive allele c. The dominant allele of another independent gene (I) inhibits
expression of color in birds with genotypes C/C or C/c. Consequently both C/- I/- and c/c -/- are
white. A colored cock is mated with a white hen and produces many offspring, all colored. Give
the genotypes and both parents and offspring.
29) If the dominant allele K is necessary for hearing, and the dominant allele M of another
independent gene results in deafness no matter what other genes are present, what
percentage of the offspring produced by the cross k/k M/m X K/k m/m will be deaf?
30) What fraction of the offspring of the parents each with the genotype K/k L/l M/m will be
k/k l/l m/m?
31) Suppose that an allele, b, of a sex-linked gene is recessive and lethal. A man marries a
woman who is heterozygous for this gene. If this couple had a large number of normal
children, what would be the predicted sex ratio of these children?
32) Red green color blindness is inherited as a sex-linked recessive disorder. If a color-blind
woman marries a man who has normal color vision, what would be the expected
phenotypes of their children with reference to this characteristic?
33) In Drosophilia melanogaster, there is a dominant allele for gray body color and a
dominant allele of another gene for normal body wings. The recessive alleles of these
two genes result in black body color and vestigial wings, respectively. Flies heterozygous
for gray body and normal wings are crossed with flies that have black bodies and
vestigial wings. The F1 progeny are then crossed, with the following results:
Gray body, normal wings 236
Black body, vestigial wings 253
Gray body, vestigial wings 50
Black body, normal wings 61
Would you say that these two genes are linked? If so, how many units apart are they on
the linkage map?