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INTRODUCTION TO GENETIC PROBLEMS
To complete the following problems, you will need to remember the following list of
terms. Test your memory by matching the term or description in the column on the right
with the meaning or example given in the column on the left. Write the number of each
answer in the space provided.
1.
2.
3.
4.
5.
6.
genotypes
homozygous dominant
homozygous recessive
heterozygous
phenotypes
purebred
____
____
____
____
____
____
RR
the gene pairs an individual
carries
the appearance of an individual,
based on the gene pairs carried
having 2 of the same alleles
for a given trait
having 2 different alleles for a given
trait
rr
PART 1
For each of the following problems below, do the following:
a.
b.
c.
d.
e.
assign symbols for each allele
write the genotypes of the parents
complete a Punnett square showing the possible offspring
list the genotypic ratios of the offspring
list the phenotypic ratios of the offspring
EXAMPLE: Cross a homozygous black rat with a homozygous white rat. Black is the
dominant form.
a.
b.
c.
B=black, b=white
BB x bb
d.
e.
1.
a.
b.
c.
In a certain species of rat, black color dominates white.
Cross two hybrid black rats.
_______ X_______
d.
e.
2.
a.
b
c.
Cross a hybrid black rat with a white one.
_______ X_______
d.
e.
3.
a.
b.
c.
In garden peas, tall plants dominate short plants. Cross a homozygous tall plant
with a short plant.
______X_______
d.
e.
4.
Cross a hybrid plant with a homozygous tall one.
a.
b.
c.
______X______
d.
e.
PART 2
In the next 2 sets of problems, the traits show incomplete dominance. This means that
neither trait is dominant; if both alleles are present, the phenotype is a blend of the 2
traits.
EXAMPLE: In guinea pigs, neither yellow nor white color dominates. They blend to
form a cream color in the heterozygote. Cross a cream colored guinea pig with a yellow
one.
a.
b.
c.
Y=yellow, W=white,
YW=cream
______X______
d.
e.
1.
a.
b.
c.
Cross a yellow guinea pig with a white one.
d.
_____X_____
e.
2.
a.
b
c.
Cross two cream colored guinea pigs.
_____X_____
d.
e.
3.
Cross two white guinea pigs.
a.
b.
c.
_____X_____
d.
e.
4.
a.
b.
c.
In certain species of chickens, black blends with white to make a speckled
plumage. Cross a black chicken with a white one. Assume both are pure
breeding for their trait.
____X____
d.
e.
5.
a.
b.
c.
Cross two speckled chickens.
_____X_____
d.
e.
6.
a.
b.
c.
Cross a speckled chicken with a black one.
______X______
d.
e.
7. Cross a speckled chicken with a white one.
a.
b.
c.
_____X_____
d.
e.