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AP BIOLOGY—Unit 5
Inheritance Patterns Answer Key
Name:
Sex-Linked Trait- a trait carried on the X or Y chromosomes-can be either dominant or
recessive.
Epistasis- A pair of alleles at one location influences (must be turned on) the expression of
another pair of alleles at a different location- both dominant and recessive traits.
Polygenic Trait- Where one trait is controlled by more than one pair of alleles.
Pleiotropy- Where one pair of alleles influences more than one trait.
Linked Genes- 2 or more alleles that are in close location on the same chromosome and are
inherited together (unless crossing over occurs) - reduces the variation in sex cells.
Multiple Alleles- More than 2 alleles exist for a gene.
Incomplete dominance- the heterozygous genotype gives a phenotype that is a mixture of the
dominant and recessive traits.
Codominance- the heterozygous genotype gives a phenotype that expresses some of both the
dominant and recessive traits.
Extranuclear Genes-genes found in the small, circular DNA of mitochondria, chloroplasts and
other plant plastids. The zygote of a plant receives all the plastids and mitochondria from the
cytoplasm of the egg, and the zygote of an animal receives all of the mitochondria from the
cytoplasm of the egg.
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For each of the following, put the names of the type of inheritance in the blank and answer the
question(s).
1. Incomplete Dominance
a. In snapdragon flowers a red and a white flower are crossed and the F1 generation is all pink.
The F2 generation yields 50 white, 48 red, and 103 pink offspring. How is this trait inherited?
(Include what, if any gene is dominant.) Show the phenotypes for all possible genotypes.
R=red
RR=Red Rr=Pink rr=White
r=white
P: RRxrr
*Neither red nor white is dom.
F1:
1Rr x Rr
1/4RR=Red 2/4 Rr=Pink 1/4rr=White
b. Familial hypercholesterolemia (FH) is an inherited form of high cholesterol in the blood
resulting in clogged arteries, heart attacks, and death. Two diseased genes result in death as a
child from heart attack, one normal gene and one diseased gene results in death as a young adult
and two normal genes do not form the type of heart disease. Show a pedigree of a family of at
least 3 generations that expresses all possible genotypes. Also note if this is a dominant,
recessive, or neither trait.
NN
NN
Nn
Nn
N= normal n=FH
NN=normal
Nn=mild
nn=death as child
Nn
Nn
nn
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2.Sex-linked Trait on X-chromosome
a. Duchenne Muscular Dystrophy is a severe form that results in muscle weakness and death
(usually due to respiratory failure by age 30.) This disease a) affects males more than females
b)affected males never pass this on to their sons c) this need not show up in all generations d)
daughters of affected males are at risk. Show a pedigree that illustrates a-d above. (is this
dominant or recessive?) Note: All N’s and n’s should be superscripts for the genotypes!
XNY
XNXn
XnY
XNXn
XNY
XNXN
XNXN
XN=normal
Xn=MD
XNXn
XNY
b. Orofacial Digital Syndrome results in abnormalities of the mouth, face, fingers, and toes. A)
males and females are affected equally b) all affected males have affected mothers and daughters
c) there is no male to male transmission. Please show a pedigree that illustrates a-c and state if
this is dominant or recessive.
Dominant
XNXn
XnY
XnY
XNXn
XNY
XnXn
XnY
XNXn
XN= O.D.S.
Xn=normal
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4. Epistasis
a. A Drosophila (Fruit Fly) pure breeding parental cross involving eyeless males and brown-eyed
females produced offspring that were eyeless in all cases. An F2 cross resulted in 1205 eyeless
flies, 303 brown-eyed flies, and 106 without eye color. *Hint: this trait involves 2 pairs of genes
on different chromosomes. Show how this trait is inherited and list all the genotypes and
phenotypes possible.
b. The F1 cross of a male agouti mouse and a female albino mouse resulted in offspring that
were all agouti. The F2 cross produced 905 agouti, 410 albino, and 299 with a black fur coat
color. *Hint: there are 2 pairs of genes involved on 2 different chromosomes. Describe how this
trait was inherited and what genotypes and phenotypes are possible.
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3. Co-Dominance
a. A pure breeding white hamster is crossed with a pure breeding brown. The F1 generation is all
brown and white spots. The F2 generation consists of 10 brown, 11 white and 19 brown and
white spots. How is this trait inherited and show all possible genotypes and phenotypes.
b. (this one is two modes combined)Co-Dominance & Multiple Alleles
Blood type is determined by a pair of alleles I and i. The dominant allele has two forms IA, and
IB, both of which express a type of protein on the red blood cells (simple called antigen A and
antigen B) Please show a pedigree in which a family has all 4 possible blood types expressed.
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5. Linked Genes
Parents showed to be dimpled and freckled. They have kids that were dimpled and freckled and
non-dimpled and non-freckled, but never dimpled without freckles. Suggest a mode of
inheritance for these two traits and show all possible genotypes for these parents. *Hint:
Consider more than one set of alleles on the same chromosome.
6. Pleiotropy
Many believe that Abraham Lincoln suffered from Marfan syndrome, which results in elongated
bone structure and weak artery walls, particularly in the aorta. His father, perhaps, suffered from
these symptoms. None of his children appeared to be affected. Please draw a pedigree that
illustrates such a family and show all genotypes possible. *Hint-This involves one pair of genes.
If Recessive
If Dominant
Nn
nn
nn
Nn
mm
M_
N?
Nn
M_
Nn
mm
mm
mm
mm