Due to limited space, work out problems on a separate sheet of
paper
MONOHYBRID CROSSES
1. In peas, yellow seed (Y) is dominant over green seed (y).
In the F2 generation of a parental cross in which a dominant homozygote
is crossed with a recessive homozygote, you would expect: a)
plants that produce 3 yellow seeds to every green seed
b) plants with one yellow seed for every green seed c) only plants
with either the genotype YY or yy d) both a and c
2. In humans, pointed eyebrows are dominant over smooth eyebrows.
Mary's father has pointed eyebrows, but she and her mother have
smooth eyebrows. What is the genotype of the father? a) BB b)
Bb c) bb
3. How can you distinguish whether an individual is a homozygous
dominant or a heterozygous dominant? Test Cross
2 TRAITS (dihybrid) which are UNLINKED
4. In guinea pigs, smooth coat (S) is dominant over rough coat
(s) and black coat (B) is dominant over white coat (b). In the
cross SsBb X SsBb, how many of the offspring will have a smooth,
black coat? a) 9 out of 16 b)
1 out of 16 c) 6 out of 16 d) all offspring will have this phenotype
5. In tomatoes, red fruit (R) is dominant over yellow fruit (r)
and tallness (T) is dominant over shortness (t). A plant that
is RrTT is crossed with a plant that is rrTt. What are the chances
of an offspring being heterozygous for both traits? a) none b)
1/2 c) 1/4 d) 9/16
6. Referring to the information of the previous question, if a
plant with an RrTt genotype is crossed with a plant that is rrtt:
a) all the offspring will be tall with red fruit b) 12 out of
16 will be tall with red fruit c) 8 out of 16 will be tall with
red fruit d) 4 out of 16 will be tall with red fruit
7. In horses, B=black coat, b=brown coat, and T=trotter, t=pacer.
A black trotter that has a brown pacer offspring is: a) BT b)
BbTt c) bbtt d) BBtt
2 TRAITS (dihybrid) which are LINKED
8. Shaggy hair in dogs is dominant to its recessive allele,
short hair, and black coat color is dominant to its recessive
allele, tan. When heterozygous black, shaggy-haired dogs are crossed
to short-haired tan dogs, progeny with the following phenotypes
are obtained: 46% shaggy and black, 44% short and tan, 5% shaggy
and tan and 5% are short and black. What is the distance between
the hair length and hair color loci? 10 map units
(or centimorgans)
9. Individuals of the genotype AaBb were mated to individuals
of genotype aabb. One thousand offspring were counted: Aabb 474
aaBb 480 AaBb 20 aabb 26
This type of cross is known as a testcross. What
are the two parental classes? Aabb, aaBb
and the two recombinant classes of offspring? AaBb,
aabb. What is the percentage of recombination between
these two loci? 4.6% How many map units
apart are they? 4.6 map units (centimorgans)
10. The frequency of crossing-over between linked genes A and
B is 35%; between B and C is 10%; between C and D is 15%; between
C and A is 25%; between D and B is 25%. The sequence of the genes
on the chromosome is: a) ACDB b) ACBD c) ABDC d) ABCD e)
ADCB
11. Gene A and gene B are known to be 10mu apart on the same chromosome.
Individuals homozygous dominant for these genes are mated with
homozygous recessives. The offspring are then test crossed. If
there are 1,000 offspring from the test cross, how many of the
offspring would you expect to show the cross-over phenotype? 100
CODOMINANCE
12. A woman with type AB blood marries a man whose mother was
type O and father type A. They have a son with type B blood. What
are the possible genotypes of the father? I(i)I(A)
or I(i)I(i) [Note: the letters in parenthesis
should be superscripts!]
13. In cattle, reddish coat color is not completely dominant to
white coat color. Heterozygous individuals have coats that are
roan colored (ie. reddish, but with spots of white hairs). Outline
a breeding procedure whereby a true breeding strain of red cattle
could be established from a roan bull and a white cow.
First cross roan bull X white cow ; Next cross the
2 roan progeny = 25% true breed red cattle
INCOMPLETE DOMINANCE
14. Yellow coat color in guinea pigs is produced by the homozygous
genotype CyCy, cream color by the heterozygous genotype CyCw,
and white by the homozygous genotype CwCw. What genotypic and
phenotypic ratios are matings between cream colored individuals
likely to produce? 1:2:1
15. When a true breeding white horse was mated with a true breeding
black horse, all the progeny were brown. What would be the phenotypic
and genotypic ratio of the F2 progeny? 1:2:1
SEX-LINKAGE
16. The X-linked barred locus in chickens controls the pattern
of the feathers, with the alleles B for barred pattern and b for
no bars. If a barred male (XBY) is mated to a nonbarred female
(XbXb), what will be the appearance of the male and female progeny?
All females=barred ; All males=no bars
17. A particular sex-linked recessive disease of humans isn't
usually fatal. Suppose that a boy 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?a) 0% b) 25% c) 50% d) 75% e)
100%
18. What are the chances that a non-color blind male from a family
with color-blindness (an X-linked recessive allele) will pass
on the color blind trait to his children? a) 50% b) 100% c)
0% d) 75% e) not enough information is given to
determine the answer
19. Princess Eugenie, who was a carrier for hemophilia, married
her cousin Prince Albert who was a hemophiliac. a) all their children
would be hemophiliacs b) half their children of both
sexes would be hemophiliacs c) all their girls would
be hemophiliacs d) all their sons would be carriers e) two of
the above
20. The hemophilia gene is located 12 map units from the red-green
colorblindness gene on the X chromosome. Red-green colorblindness
is recessive to normal color vision. A woman with normal blood
clotting and normal color vision, but whose father was a hemophiliac
and whose mother was red-green colorblind, marries a man who is
not a hemophiliac and is not colorblind. What percent of their
children will be colorblind and have hemophilia? a) 50% b) 12%
c) 6% d) 3% e) too little information
to predict.