Download 1. A form of a gene is called a(n) ______. (For example, the gene for

1. A form of a gene is called a(n) _________.
(For example, the gene for flower color in pea
plants has two forms, one for purple and one
for white. These are possible ________ for
this gene.)
A.
B.
C.
D.
Genotypes
Genomes
Alleles
Proteomes
2. A recessive allele is
A. a form of a gene that is always expressed
B. a form of a gene that can be hidden
C. the allele that must be less common in the
population
D. both B and C
Recessive traits are often less common in the
population, because they are only expressed if an
organism is heterozygous.
However, natural selection can affect how prevalent
(common) each allele is in the population. If most
individuals have the recessive alleles this trait will be
most common.
Example: Dwarfism (Achrondplastic) is caused by a
dominant allele but is very rare.
3. Describing the physical appearance/
expression of a trait defines the
_______________ of the individual.
A.
B.
C.
D.
Phenotype
Genotype
Prototype
Gene pool
4. Identifying the two alleles possessed
by an individual for a trait (such as Rr)
defines their __________________ .
A.
B.
C.
D.
Phenotype
Genotype
Prototype
Gene Pool
5. An organism with two different
alleles for a trait such as (Gg) is called
A.
B.
C.
D.
Homozygous
Heterozygous
Haploid
Diploid
The prefix hetero= different.
A heterozygous genotype is one where the individual has
two different alleles (forms of the gene) for a trait.
6. Which of the following is true
regarding the genotype of an
individual with a dominant phenotype
for a trait?
A. It must be homozygous
B. It must be heterozygous
C. It could be homozygous or
heterozygous
7. Which of the following is true regarding
the genotype of an individual with the
recessive phenotype for a trait.
A. It must be homozygous
B. It must be heterozygous
C. It could be homozygous or heterozygous
The black fur allele is dominant in rabbits.
Rabbits will have dark fur whether they have one
black allele or two. (Homozygous dominant or
heterozygous will look the same.)
Rabbits can only have white fur if both of their alleles
are the recessive white fur allele.
(Must be homozygous recessive.)
8. Which of the following is the correct way to set
up a Punnett square for a cross of two cats that are
both heterozygous for bushy tails? The bushy tail
allele is B and the nonbushy tail allele is b.
A. .
B. .
C. .
Bb
Bb
B
B
B
b
Bb
Bb
b
b
B
b
Each side of the Punnett square
represents the possible alleles that
can be passed down from one
parent.
o
Since each gamete (egg or sperm)
has only one allele for each gene,
only one letter should be placed
over each square.
o
A heterozygous parent has one of
each allele, so 50% of the gametes
have one allele and 50% of the
gametes have the other.
Mother’s egg
B
b
Father’s sperm
o
B
b
9. If the purple flower allele (P) is dominant
and the white flower allele is recessive (p),
can two plants with purple flowers produce
a seed for a plant with white flowers?
A. Yes
B. No
If both are heteozygous for the trait,
they may each pass down the white
allele.
10. If the purple flower allele (P) is
dominant and the white flower allele is
recessive (p), can two plants with white
flowers produce a seed for a plant with
purple flowers?
A. Yes
B. No
Since the white flower is the recessive allele,
plants with this recessive trait must have two
recessive alleles, and therefore do not have
any purple flower alleles to pass down.
X
=
11. The widow’s peak allele is dominant (W), the
nonwidow’s peak allele is recessive (w). If one parent is
heterozygous for the allele (Ww) and the other parent
does not have a widow’s peak (ww). What is the
probability that their first child has a widow’s peak?
(Hint: Draw a Punnett square)
A.
B.
C.
D.
E.
100%
75%
50%
25%
0%
w
w
W
Ww
Ww
w
ww
ww
2 out of 4 = 50%
12. The parent’s from the previous
problem have two children with widow’s
peaks. What is the probability that their
third child will have a widow’s peak?
A.
B.
C.
D.
E.
100%
75%
50%
25%
0%
13. Hitchhiker’s thumb is a recessive trait (t).
A nonhitchhiker’s thumb is dominant (T).
If two parents are heterozygous for
the trait, what is the probability
that they will have a child with a hitchhiker’s
thumb?
A.
B.
C.
D.
E.
100%
75%
50%
25%
0%
T
t
T
TT
Tt
t
Tt
tt
1 out of 4 (25%) probability to inherit recessive
alleles from both parents.
14. The leg-headed (legs instead of antennae)
allele is recessive in fruit flies (a).
If a homozygous dominant fruit fly for the
normal phenotype (AA) is mated with a legheaded fruit fly (aa), what is the probability
that they will have leg-headed offspring?
A.
B.
C.
D.
E.
100%
75%
50%
25%
0%
Normal fruit fly
Leg-headed fruit fly
(antennaepedia)
A
A
a
Aa
Aa
a
Aa
Aa
All the offspring will inherit a dominant allele
from the homozygous dominant fruit fly.
Therefore they can not have an offspring with
the recessive trait.
15. A true-breeding yellow flowered plant is
crossed with a true-breeding white flowered
plant. The F1 generation has all yellow
flowers. What is the probably outcome for
the F2 generation?
A.
B.
C.
D.
E.
All yellow
All white
50% yellow, 50% white (1:1)
75% yellow, 25% white (3 yellow: 1 white)
75% white, 25% yellow (3 white: 1 yellow)
• The true-breeding plants must be homozygous. (YY x
yy)
• The F1 generation must be heterozygous (Yy). Yellow
must be dominant.
• The F2 produced by the F1 cross (Yy x Yy) should have a 3
to 1 phenotype ratio of yellow to white.
Y
y
Y
YY
Yy
y
Yy
yy
16. What is the genotype ratio from a
cross of two plants that are heterozygous
for round seeds (R= round, r = wrinkled).
A.
B.
C.
D.
3:1
1:1
1:2:1
9:3:3:1
Egg
Pollen
R
r
In a heterozygous cross, 3
genotypes can be produced: RR,
Rr or rr.
R
RR
Rr
The probabilities are:
r
Rr
rr
1 out of 4 RR
2 out of 4 Rr (can inherit R from
egg and r from pollen or r from egg
and R from pollen)
1 out of 4 rr_________________
1:2:1 ratio
17. The allele for purple flowers is dominant (P)
in peas. White is recessive (p). If you have a pea
plant with purple flowers which you want to
determine is heterozygous or homozygous,
which of the following is true?
A. It must be homozygous
B. It must be heterozygous
C. You could perform a test cross, which
is usually crossing with a recessive
plant
D. You could perform a test cross, which
is usually crossing with a
homozygous dominant plant
A test cross can be used to determine the genotype of a
organism with a dominant phenotype.
• It involves crossing with a recessive.
• Recessive offspring can only be produced if the organism is
heterozygous.
• If the results are all offspring with the dominant
phenotype, the test may be inconclusive (unless there is a
very large number of offspring)
•
1.C
9.A
2. B
10.B
3. A
11.C
4. B
5. B
6. C
12.C
13. D
14. E
15. D
7. A
16. C
8. C
17.C