- One or more of the three children will have disease 1. - All three children will have the disease. - At least one child out of three will be phenotypically normal.

1. • all three of their children will be of normal phenotype
• one or more of the three children will have the disease 1.
• all three children will have the disease
• at least one child out of three will be phenotypically normal
Name Date
Genetic Practice Problems
Monohybrid
1. In 1981, a stray black cat with unusual rounded curled-back ears was adopted by a
family in California. Hundreds of descendants of the cat have since been born, and cat
fanciers hope to develop the "curl" cat into a show breed. Suppose you owned the first
curl cat and wanted to develop a true breeding variety.
• How would you determine whether the curl allele is dominant or recessive?
• How would you select for true-breeding cats?
• How would you know they are true-breeding?
2. Phenylketonuri (PKU) M
i
en inherited disease caused by a recessive allele. If a woman
and her husband are both carriers, what is the probability of each of the following?
Incomplete
3. Thalassemia is an inherited anemic disorder in humans. Individuals can be completely
normal, they can exhibit a "minor" anemia, or they can exhibit a "major" anemia.
Assuming that only a single gene pair and two alleles are involved in the inheritance of
these conditions answer the following.
• Which phenotype is recessive?
• Complete a cross between a man that exhibits "minor" anemia and a female that is
normal. What is the phenotypic and genotypic ratio for their offspring?
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2. a. Red x red
b. White x white
. Red x white
d. Roan x roan
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b
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In shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate
phenotype expressed as a mixture of red and white hairs. The following data was
obtained from various crosses.
all red
all white
all roan
% red:% roan:% white
What are the genotypes of parents and offspring for each cross?
Codominant
5. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur
together)
• What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?
51
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Multiple Alleles
6. A man with group A blood marries a woman with group B blood. Their child has group 0
blood.
• What are the genotypes of these individuals?
• Complete the Punnett Square. Whatrhei genotypes and in what frequencies, would
you expect in offspring from this marnage?
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7. Color pattern in a species of duck is determined by one gene with three alleles. Alleles H
and I are codominant, and allele i is recessive to both. How manyhe
-notypeipare
possible in a flock of ducks that contains all the possible combinations of these three
alleles? r r G
‘ r'tkOk C-TC, Ott
, I
„
rsi ) --)

3. 6. A color-blind son .1
7. A color-blind daughter
8. A woman sues a man for child support, claiming that he is the father of her illegitimate
child. The woman is type A, the child is type 0, and the man is type AB. Could he be
the father of her child? Show why or why not.
at‘T-k ar X ri
9. Imagine that a newly discovered, recessively inherited disease is expressed only in
individuals with type 0 blood, although the disease and blood group are independently
inherited. A normal man with type A blood and a normal woman with type B blood have
already had one child with the disease. The woman is now pregnant for a second time.
What is the probability that the second child will also have the disease? Assume both
parents are heterozygous for the "disease" gene.
11
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Sex Linked
10. A husband and wife have normal vision, although both of their fathers are red-green
color-blind, which is inherited as an X-linked recessive condition. What is the probability
that the first child will be:
1. A normal son _L- 25/
2. A normal daughter-Iz I501
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4. 11. In Drosophila, an X-linked recessive mutation, scalloped, causes irregular wing margins.
Diagram the F1 and F2 results if:
1. A scalloped female is crossed with a normal male
2. A scalloped male is crossed with a normal female.
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3. Compare these results to those that would be obtained if scalloped were not
X-linked.
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12. In alley cats, the coat color is determined by a gene carried on the X chromosome. At the
same time, the alleles are expressed as intermediate (nondominance) inheritance.
- Genotypes and color are as follows: Females: Xb XID,= yellow Males: Xb Y = yellow XB
vF!)—?Aart Xb = calico XB Y = black XB XB = black
9 A calico cat has a litter of eight kittens: one yellow male, two black males, two yellow
ifemales, and three calico females. What is the color of the father of the litter?
CD e WOW) D
I
ACK Vt567-
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(L k)
A black cat has a litter of seven kittens: three black males, one black female, and three
calico females. Comment on the probable paternity of this litter and explain.
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b(
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A yellow cat has a litter of four kittens: one yellow, and three calicos. Assuming a single
father for the litter, what is the sex of the yellow kitten?
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5. PPLI PPLI
P PfL
• 323 three-pod normal, 106 three-pod wrinkled (3
X p LI
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Dihybrid
METHOD 1:
13. In sesame plants, the one-pod condition (P ) is dominant to the three-pod condition (p),
and normal leaf (L) is dominant to wrinkled leaf (I) . Pod type and leaf type are inherited
independently. Determine the genotypes for the two parents for all possible matings
• 318 one-pod normal, 98 one-pod wrinkled ( )
producing the following offspring:
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s73 t-
+0
• 401 one-pod normal" 7C71..— P LL
VS'LL t)vil P UyFR,
• 150 one-pod normal, 147 one-pod wrinkled, 51 three-pod normal, 48 three-pod wrinkled /
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1)
• 223 one-pod normal, 72 one-pod wrinkled, 76 three-pod normal, 27 three-pod wrinkled C.'4. :
Pp L‘ X
14. In some plants, a true-breeding, red-flowered strain gives all pink flowers when crossed
with a white-flowered strain: RR (red) x rr (white) --> Rr (pink).
If flower position (axial or terminal) is inherited as it is in peas what will be the ratios of
genotypes and phenotypes of the generation resulting from the following cross: axial-red
(true-breeding) x terminal-white?
What will be the ratios in the F2 generation? KW-4 OIA VT
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6. METHOD 2:
15. Flower position, stem length, and seed shape were three characters that Mendel studied.
Each is controlled by an independently assorting gene and has dominant and recessive
expression as follows:
Character Dominant Recessive
Flower:ifposition g '' al
Stem length Tail (T) Dwarf (t)
Seed shape Round il
• If a plant that is heterozygous for all three characters were allowed to self-fertilize, what
proportion of the offspring would be expected to be as follows: (Note - use the rules of
probabilitOnd show your work) instead of huge Punnett squares)
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, r
T
ift
a
homozygous for the three inant trait homozygous for the three recessive
traits I -I--
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r c/461,
heterozygous I 2- -2_
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4-- -
c
o
t
homozygous for axi I and tall, h eroz seed shape
)c-Dr-a' 64 7.
16. The genotype of Fl individuals in a tetrahybrid erossase AaBbCcDd. Assuming
independent assortment of these four genes, what are the probabilities that F2 offspring
would have the following genotypes?
0
j_
• aabbccdd 4_ X 15 co
2
• AaBbCcDd
-2:4 X ?
Or 7-1 ZS co
• AABBCCDD j
r..E 4
4. c0
k x
• AaBBccDd
• AaBBCCdd

7. 17.In mice, black color (B ) is dominant to white (b ). At a different locus, a dominant allele (A)
produces a band of yellow just below the tip of each hair in mice with black fur. This gives a
frosted appearance known as agouti. Expression of the recessive allele (a ) results in a
solid coat color. If mice that are heterozygous at both loci are crossed, what will be the
expected phenotypic ratio of their offspring?
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Polygenic
18.The weight of the fruit in one variety of squash is determined by two pairs of genes. The
homozygous dominant condition, AABB, results in 4-pound squashes, and the
homozygous recessive condition, aabb, results in 2-pound squashes. Each dominant
gene adds% pound to the minimum 2-pound weight. What would be the weights and
ratios of a cross between two individuals that are heterozygous for both traits?
4 POUNDS
—1
+
-
3.5 POUNDS
3 POUNDS
2.5 POUNDS
—1
"-
2 POUNDS
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Linked
19. You are doing a genetics experiment with the fruit fly. In the P generation you cross 2
true breeding flies. The female is brown and wingless and the male is black with normal
wings. All of the flies of the Fl generation are brown with normal wings (.PON)
Dorn br3vi ntnoreno, ?Skacv-PM
Identify the
the:senotypes of the parents:
13--siown
female: 36 ao, male: 60
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rr-n0Ylri a=maesi
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Srouu PI/POT te
l t
You now take an Fl female and cross her to a true breeding black, wingless male. The
resulting 1600 offspring in the F2 generation are:
° 85 brown win ed B_A -
dok—
V. (3.....ac‘
:_175fflack wingless bb0,a
cap()
What is the recombination frequency between the color and wing genes?
ithp
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