Biology 20
Practice Genetic Problems Answers
a) a
self-cross; b) a test cross; c) a hybrid cross; d) an F1
cross; e) a dihybrid cross.
2. In crossing a homozygous recessive with a heterozygote, what is the
chance of getting a homozygous recessive phenotype in the F1 generation?
a)
zero; b) 25%; c) 50%; d)
75%; e) 100%.
3. In snapdragons,
heterozygotes have pink flower, whereas homozygotes have either red or white
flowers.When plants with red flowers are crossed with plant with white flowers,
what proportion of the offspring will have pink flowers?
a)
zero; b) 25%; c) 50%; d) 75%;
e) 100%.
4. Black fur in mice
(B) is dominant to brown fur (b) short tails (T) is dominant of long tails (t).What
proportion of the progeny of the cross BbTt x Bbtt will have black fur and long
tails?
a)
1/16; b) 3/16; c) 3/8; d)
1/2; e) 9/16.
5. A couple has three
children, all of whom have brown eyes and blond hair.Both parents are homozygous
for brown eyes (BB), but one is blond (rr) and the other is a redhead (Rr).What
is the probability that the next child will be a brown-eyed redhead?
a)
1/16; b) 1/8; c) 1/4; d) 1/2;
e) 1.
6. A 9:3:3:1 ratio is
characteristic of the: a) F2 generation of a monohybrid cross;
b) F2 generation of
a momhybrid cross; c) F1 generation of a dihybrid cross;
d) F2 generation
of a dihybrid cross; e) F2 generation of a trihybrid cross.
7. How many unique
gametes could be produced through independent assortment by an individual with
the genotype Aa Bb CC Dd EE?
a)
4; b) 8; c) 16; d)
32; e) 1/64.
8. In cattle, roan
color (mixed red and white hairs) occurs in the heterozygous (Rr) offspring of
red (RR) and white (rr) homozygotes.When two roan cattle are crossed, the
phenotypes of the progeny are found to be in the ratio of one red: two roan: one
white.Which of the following crosses could produce the highest percentage of
roan cattle?
a) red x
white; b) roan x roan; c) white x
roan; d) red x roan
e) all of the above
crosses would give the same percentage of roan.
9. Roan color in cattle
is the result of absence of dominance between red and white color genes.How
would one produce a herd of pure-breeding roan-color cattle?Explain.
a)cross roan with
roan; b) cross red with white; c) cross roan with
red;
d) cross roan with
white; e) it cannot be done.
10. An animal has the
genotype AaBbCcDd.Relative to these four unlinked loci, how many unique gametes
can be produced by this individual?
a)
1; b) 2; c) 4;
d) 8; e) 16.
11. In some cats, black
color is due to a sex-linked (X-linked) recessive gene (b); the dominant allele
(B) produces orange color.The heterozygote (Bb) is calico.What kinds of
offspring would be expected from the cross of an orange male and a black female?
a) black females,
orange males; b) orange females, black males;
c) calico
females, black males; d) black females, calico males;
e) orange females
and males.
12. People who have red
hair usually have freckles.This can be explained by?
a)
linkage; b)
reciprocal translocation; c) independent assortment;
d) sex-influenced
inheritance; e) nondisjunction.
13. In humans, the
allele for short fingers is dominant over that for long fingers.If a person with
short fingers who had a parent with long fingers marries a person with long
fingers, what are the chances for each child to have short fingers?
a)
zero; b) 25%; c) 50%; d)
75%; e) 100%.
14. If a woman who is
red-green colorblind mates with a man with normal vision, what phenotypes would
one expect their children to have?
a) all their
children would be color blind;
b) all their
daughters will be color-blind, but all their sons will have normal vision.
c) all their
daughters will be carriers and all their sons will be color-blind.
d) all their
daughters will have normal vision and will not be carriers, but all their sons
will be color-blind.
e) half their
daughters will be carriers and the other half will be fully normal; half their
sons will be color-blind and the other half will have normal vision.
15. If a child has AB
blood type, the parents:
a) must both have
different blood types;
b) must be A and B
but not AB;
c) must both be AB;
d) can be any blood
type, but must be different;
e) can both be
AB or must be different and neither can be type O.
16. Two individuals that
are heterozygous for A and B blood types respectively have children.Which of the
following are possible blood types of their children?
a)
A; b) B; c) AB; d) O; e)
all of these are possible.
17. Ellie May, a mother
with type B blood, has a child with type O blood.She claims that Jethro, who has
type A blood, is the father.He claims that he cannot possibly be the
father.Further, blood tests ordered by the judge reveal that the father is
homozygous.The judge rules that:
a) Ellie May is
right and Jethro must pay up.
b) Jethro is
right and is a winner-winner (chicken dinner).
c) Ellie May cannot
be the real mother of the child.There must have been an error made at the
hospital.
d) It is impossible
to reach a decision based on the limited data available.
e) none of these
are correct.
18. If a daughter
expresses a sex-linked recessive gene, she inherited the trait from:
a) her
mother; b) her father; c) both parents;
d) neither parents.
19. A blue-eyed,
left-handed woman marries a brown-eyed, right handed man who is heterozygous for
both traits.If blue eyes and left-handedness are recessive, how many different
phenotypes are possible in their children?
a)
one; b) two; c) three; d)
four; e) six; ab) eight; ac)
nine; ad) too many.
20. What are the
phenotypes from question #19?
Brown eyed/righty
(BbRr) � brown eyed/lefty (Bbrr) � blue eyed/righty (bbRr) � blue eyed/lefty (bbrr)
21. A married couple
both has normal color vision, but their daughter has red-green colorblindness, a
X-linked recessive trait.The husband sues the wife for divorce on grounds of
infidelity.Can genetics provide evidence supporting his case?Explain.
22. Joe Bob has
unattached earlobes like his father, but his mother has attached earlobes.Give
the genotypes of each of the three.Unattached ear lobes are dominant to attached
earlobes.
Phenotype Genotype
Joe Bob -
unattached Uu
Father -
unattached UU or Uu
Mother -
attached uu
23. IN guinea pigs,
black hair (B) is dominant to white (b).Two black guinea pigs of the same
genotype were mated and produced 29 black and 9 white offspring.What would you
predict the genotypes of the parents to be?Explain.
B b
B BB Bb
b Bb bb
24. Two individuals are
both heterozygous for a single pair of genes (Tt).During the course of their
marriage, they produced 8 offspring.Approximately how many (give me a number,
not a percentage) of the offspring can be expected to display the dominant
phenotype?